SpeedTree 是一套程序化植被建模工具链，由 Interactive Data Visualization（IDV）公司开发。它的核心思路不是“手工雕刻一棵树”，而是用规则描述一棵树怎么长：你告诉软件“主干每 0.5 米分出一根侧枝，侧枝与主干的夹角在 45°～70° 之间随机，侧枝长度是主干的 40%"，软件就按这套规则把树生成出来。

这样做的好处有三个：

• 可无限变化——同一套规则换一个随机种子就是另一棵树，批量产出整片森林不需要重复劳动。
• 面数可控——从规则到网格的每一步都能控制精度，同一棵树可以同时输出游戏用的几万面和影视用的几百万面。
• 引擎原生支持——Unreal Engine 和 Unity 都内置了 SpeedTree 的运行时，风力动画、LOD 切换、公告板都是引擎直接支持的。

SpeedTree 的产品线大致分为三块：

产品	作用
SpeedTree Modeler	建模工具，本教程的主角。用来制作单株植物、树丛、草地，并导出到引擎或渲染器。
SpeedTree SDK / Runtime	引擎端的运行时库，负责风力动画、LOD、公告板的实时计算。UE 与 Unity 已内置。
SpeedTree Store / 资源库	官方与第三方售卖的成品植被模型库，可直接购买使用，也可以买来拆解学习。

SpeedTree 擅长什么，不擅长什么

擅长	不擅长
树木、灌木、草、藤蔓、棕榈等有生长规律的植物	单株造型极其独特的雕塑感植物（更适合直接建模）
大批量、多变异地生成同类植物	完全写实的特写树皮细节（需配合摄影测量或置换贴图）
游戏与影视中需要风动与 LOD 的植被	非植物类的自然物（岩石、地形、水体需用别的工具）

SpeedTree is a procedural vegetation modeling toolchain developed by Interactive Data Visualization (IDV). Its core idea is not “hand-sculpt a tree” but rather describe in rules how a tree grows: you tell the software “the trunk puts out a side branch every 0.5 meters, the angle between side branch and trunk is randomly between 45° and 70°, and the side branch is 40% of the trunk's length,” and the software generates the tree from those rules.

That approach pays off in three ways:

• Endless variation — the same rule set with a different random seed is a different tree, so producing an entire forest in bulk takes no repeated labor.
• Controllable polygon count — every step from rules to mesh has controllable precision, so the same tree can output tens of thousands of triangles for a game and millions for film.
• Native engine support — Unreal Engine and Unity both ship the SpeedTree runtime, so wind animation, LOD switching and billboards are supported directly by the engine.

The SpeedTree product line breaks down into roughly three parts:

Product	Role
SpeedTree Modeler	The modeling tool, and the star of this tutorial. Used to author individual plants, tree clusters and grass, then export to an engine or renderer.
SpeedTree SDK / Runtime	The engine-side runtime library that handles real-time wind animation, LOD and billboards. Already built into UE and Unity.
SpeedTree Store / asset library	Libraries of finished vegetation models sold by IDV and third parties. Buy them ready to use, or buy them to take apart and learn from.

What SpeedTree is good at, and what it is not

Good at	Not good at
Trees, shrubs, grass, vines, palms and other plants that follow growth rules	One-off sculptural plants with a highly distinctive silhouette (better modeled by hand)
Generating many variations of the same species in bulk	Fully photoreal close-up bark detail (needs photogrammetry or displacement maps)
Vegetation that needs wind and LOD in games and film	Non-plant natural objects (rocks, terrain and water need other tools)

SpeedTree Modeler 的界面是典型的 Qt 停靠面板布局。下图是本机 v10.2.0 打开官方示例 Broadleaf_Field.spm 时的真实界面：

界面可以分成五个区域：

区域	位置	作用
菜单栏	最上方	File / Edit / Tools / Window / Help 五个菜单。几乎所有功能都能在这里找到，也是记忆快捷键时的兜底入口。
Generation 面板	左上	显示整棵树的节点树。所有生成器的父子层级都在这里，是操作最频繁的面板。顶部有 Add（添加节点）、Actions（节点操作菜单）、Randomize（随机化）三个按钮。
Properties 面板	左下	显示当前选中节点的全部可调参数。顶部有 Search properties.. 搜索框，参数按组（Generation、Spine、Wind…）折叠显示。
3D 视图区	中间	实时预览。左侧显示模型统计（面数、骨骼数），可切换透视/正交。
工具栏	视图上方	模式与显示控制，见下表。

下面是 Generation 面板与 Properties 面板的实际截图（从上面的主界面截取放大）：

工具栏按钮逐项说明

下面这些名称来自 v10.2.0 工具栏的真实文字：

按钮	功能
Mode　Generator / Node	切换操作对象。Generator 模式下点击视图选中的是“生成器”（整根枝条）；Node 模式下可以选中单个控制点或顶点，做精细调整。
View	视图显示选项：透视图/正交图切换、网格、参考图等。
Edit　Add / Post	Add 用于添加几何；Post 用于后处理显示（如线框叠加）。
Freehand	手绘模式开关。开启后可以像画画一样直接拖出枝条走向。
Render	渲染模式选择（光照模式、材质通道、顶点色、风力权重等），详见“渲染模式”章节。
Show	显示开关：是否显示叶片、是否显示骨架、统计信息等。
Zoom	框选放大、缩放到全模型。
Visibility	可见性控制，配合 LOD 与剔除使用。
Collision	碰撞体显示与生成开关。
Season	季节切换（春/夏/秋/冬），用于预览季节贴图与落叶效果。
Shade	着色控制。
LOD	LOD 预览与级别切换。
Scene / Scene Objects	场景对象管理，可放置参考模型、灯光、相机。

视图区统计信息

视图区左上角会实时显示模型统计，这是判断“模型是否过重”的第一手数据。以上面的示例为例：

POLYGONS - MODEL
  branches:    670,083 tris
  caps:            437 tris
  leaf meshes: 2,362,002 tris
  TOTAL:       3,032,522
  bones:               9

可以看到叶片占了绝大多数面数（约 78%）。这正是 SpeedTree 优化的核心战场：控制叶片数量与叶片网格精度，比控制枝条分段数收益大得多。

The SpeedTree Modeler interface is a typical Qt docked-panel layout. Below is the actual interface of v10.2.0 on this machine with the official sample Broadleaf_Field.spm open:

The interface divides into five areas:

Area	Location	Purpose
Menu bar	Top	Five menus: File / Edit / Tools / Window / Help. Almost every feature can be found here, and it is the fallback when you are learning shortcuts.
Generation panel	Upper left	Shows the tree's node tree. Every generator's parent/child hierarchy lives here, which makes it the most-used panel. The top has three buttons: Add, Actions and Randomize.
Properties panel	Lower left	Shows every adjustable parameter of the currently selected node. The top has a Search properties.. box, and parameters are shown in collapsible groups (Generation, Spine, Wind…).
3D viewport	Center	Real-time preview. The left side shows model statistics (triangle count, bone count), and you can toggle perspective/orthographic.
Toolbar	Above the viewport	Mode and display controls; see the table below.

Below are actual crops of the Generation and Properties panels (taken from the main interface above and enlarged):

Toolbar buttons, one by one

These names come from the actual toolbar text in v10.2.0:

Button	Function
Mode　Generator / Node	Switches what you are operating on. In Generator mode, clicking in the viewport selects a generator (a whole branch); in Node mode you can select an individual control point or vertex for fine adjustments.
View	Viewport display options: perspective/orthographic toggle, grid, reference images and so on.
Edit　Add / Post	Add is for adding geometry; Post is for post-processing display (such as a wireframe overlay).
Freehand	Toggles freehand mode. With it on you can drag out branch paths as if drawing.
Render	Render mode selection (lighting model, material channels, vertex color, wind weights…), covered in the “render modes” section.
Show	Display toggles: whether to show leaves, whether to show the skeleton, statistics and so on.
Zoom	Marquee zoom and zoom to fit the whole model.
Visibility	Visibility control, used together with LOD and culling.
Collision	Toggles display and generation of collision bodies.
Season	Season switching (spring/summer/autumn/winter) for previewing seasonal textures and leaf fall.
Shade	Shading control.
LOD	LOD preview and level switching.
Scene / Scene Objects	Scene object management; you can place reference models, lights and cameras.

Viewport statistics

The top-left of the viewport shows live model statistics — your first-hand data for judging whether a model is too heavy. Using the sample above:

POLYGONS - MODEL
  branches:    670,083 tris
  caps:            437 tris
  leaf meshes: 2,362,002 tris
  TOTAL:       3,032,522
  bones:               9

Leaves account for the overwhelming majority of the polygons (about 78%). This is exactly where SpeedTree optimization is fought: controlling leaf count and leaf mesh precision pays off far more than controlling branch segment counts.

SpeedTree 里的一切都组织成一棵节点树。理解这棵树是掌握这个软件的关键。

三种节点角色

1. 根节点（Tree）——有且只有一个，位于最顶层，存放全局设置。它不能删除、不能移动。
2. 生成器（Generator）——真正产生几何体的节点，如 Branch、Frond、Leaf Mesh、Cap。每个生成器都“挂”在某个父级下面，按父级的形状来生长。
3. 辅助节点——不直接产生主体几何，而是提供参考或转换能力，如 Target（目标点）、Zone（区域）、Conversion-Tools（转换工具）。

父子关系与层级（Level）

节点树的层级决定了“谁长在谁身上”：

• Level 0 永远是 Tree 根节点。
• Level 1 通常是树干（Trunk）。
• Level 2 是主枝，Level 3 是侧枝，依次类推。
• 叶片、羽叶通常挂在 Level 4 以上的末梢枝上。

实测数据可以印证这个结构。在本机 77 个官方示例文件里，各生成器出现的层级分布是：

生成器	实际出现的层级	说明
Tree	0	唯一根节点
Branch	1 – 7	从树干一直细分到 7 级细枝
Cap	1 – 8	跟随枝条末端
Frond	1 – 8	棕榈/蕨类可在多级出现
Leaf Mesh	1 – 11	层级最深，因为叶片挂在末梢
BatchedLeaf	1 – 8	批量叶片
Knot / Decal	1 – 6	表面装饰，跟随树干与主枝
MeshDetail	1 – 3	细节网格，通常靠近主干

节点的三种状态

状态	表现	如何切换
普通	正常显示与生成	—
隐藏（Hidden）	节点图标变暗，不生成几何	右键菜单 → Toggle visibility，或按 H
折叠（Collapsed）	该节点的所有子节点被收起，不再生成	节点前的三角箭头

节点操作菜单（Actions）

选中节点后点 Actions 按钮，或直接右键，可以看到完整的节点操作。v10.2.0 的实际菜单项包括：

菜单项	快捷键	作用
Copy / Cut / Paste	Ctrl+C / Ctrl+X / Ctrl+V	复制、剪切、粘贴节点
Paste into	Ctrl+Shift+V	把剪贴板节点粘贴为当前节点的子节点
Duplicate	Ctrl+D	原地复制一份
Delete	Del	删除节点
Rename	—	重命名（做复杂模型时务必用，否则节点名会重到无法辨认）
All like selected	Shift+L	选中所有“同类”节点（同一模板的实例）
All descendants	Shift+D	选中全部子孙节点
All like selected at this level	—	选中同层级的同类节点
All like selected, same color	—	按节点颜色筛选同类
Save selected as template...	—	把当前节点及其子树保存成模板（.stt），可在别的树里复用
Add geometry to selected	—	给选中节点挂上几何体
Clear node edits	—	清除该节点上的手工编辑，回到纯程序化状态
Clear freehand edits	—	清除手绘笔迹
Clear variances	—	清除所有方差设置
All gaussian / uniform / blended / cohesive	—	把方差类型批量改成高斯/均匀/混合/内聚
Randomize selected	—	随机化选中节点（不选则随机化整棵）
Toggle visibility	—	显示/隐藏
Select and reveal hidden nodes	—	找出并选中所有被隐藏的节点
Select nodes with edits	—	找出所有被手工编辑过的节点
Layout generators	—	自动排布节点树布局
Make all generator names unique	—	批量把重名节点改成唯一名
Upgrade legacy generator(s)...	—	把旧版本节点升级为当前版本
Icon colors	—	给节点图标设置颜色，便于在复杂树里辨认

Everything in SpeedTree is organized as a node tree. Understanding that tree is the key to mastering the software.

The three node roles

1. Root node (Tree) — there is exactly one, at the very top, holding global settings. It cannot be deleted or moved.
2. Generator — the nodes that actually produce geometry, such as Branch, Frond, Leaf Mesh and Cap. Each generator hangs under some parent and grows according to that parent's shape.
3. Helper nodes — nodes that do not directly produce the main geometry but provide reference or conversion capability, such as Target, Zone and Conversion-Tools.

Parent/child relationships and levels

The hierarchy of the node tree determines who grows on whom:

• Level 0 is always the Tree root node.
• Level 1 is usually the trunk.
• Level 2 is the primary branches, Level 3 the secondary branches, and so on.
• Leaves and fronds usually hang on twigs at Level 4 and beyond.

Measured data backs this structure up. Across the 77 official sample files on this machine, the level distribution for each generator is:

Generator	Levels observed	Notes
Tree	0	the single root node
Branch	1 – 7	from the trunk all the way down to 7th-order twigs
Cap	1 – 8	follows branch tips
Frond	1 – 8	palms and ferns can carry fronds at several levels
Leaf Mesh	1 – 11	the deepest level, because leaves hang on the tips
BatchedLeaf	1 – 8	batched leaves
Knot / Decal	1 – 6	surface decoration, follows the trunk and primary branches
MeshDetail	1 – 3	detail meshes, usually near the main trunk

The three node states

State	Appearance	How to switch
Normal	displayed and generated normally	—
Hidden	the node icon dims and no geometry is generated	context menu → Toggle visibility, or press H
Collapsed	all child nodes of this node are collapsed and no longer generated	the triangle arrow in front of the node

The node Actions menu

Select a node and click the Actions button, or just right-click, to see the full set of node operations. The actual menu items in v10.2.0 are:

Menu item	Shortcut	Purpose
Copy / Cut / Paste	Ctrl+C / Ctrl+X / Ctrl+V	copy, cut and paste nodes
Paste into	Ctrl+Shift+V	paste the clipboard node as a child of the current node
Duplicate	Ctrl+D	duplicate in place
Delete	Del	delete the node
Rename	—	rename (essential on complex models, or node names become impossible to tell apart)
All like selected	Shift+L	select all “same kind” nodes (instances of the same template)
All descendants	Shift+D	select all descendant nodes
All like selected at this level	—	select same-kind nodes at the same level
All like selected, same color	—	filter same-kind nodes by node color
Save selected as template...	—	save the current node and its subtree as a template (.stt) for reuse in other trees
Add geometry to selected	—	attach geometry to the selected node
Clear node edits	—	clear the manual edits on that node and return to a purely procedural state
Clear freehand edits	—	clear freehand strokes
Clear variances	—	clear all variance settings
All gaussian / uniform / blended / cohesive	—	batch-change variance types to gaussian/uniform/blended/cohesive
Randomize selected	—	randomize the selected node (or the whole tree if nothing is selected)
Toggle visibility	—	show/hide
Select and reveal hidden nodes	—	find and select all hidden nodes
Select nodes with edits	—	find all nodes that have been manually edited
Layout generators	—	auto-arrange the node tree layout
Make all generator names unique	—	batch-rename duplicate node names to unique ones
Upgrade legacy generator(s)...	—	upgrade nodes from older versions to the current version
Icon colors	—	set colors for node icons so they are easy to pick out in a complex tree

SpeedTree 的参数不只是“一个数字”。同一个参数可以是一个固定值，也可以是一条曲线、一组带随机分布的范围。理解这一点，才能理解为什么 SpeedTree 的树看起来不重复。

四种参数形态

形态	表现	用途
标量值 Value	一个数字输入框	所有实例都用同一个值，如“枝条长度 = 1.2"。
曲线 Curve	一个可拖控制点的小图	让参数沿父级位置或节点长度变化。详见下一节。
方差 Variance	值旁边的第二个输入框	给参数加随机范围。方差算法可选 Gaussian（高斯，集中在中心）、Uniform（均匀）、Blended（混合）、Cohesive（内聚，相邻节点保持一致）。
随机种子 Random Seed	整数	决定整个随机序列。改一个数字就能得到形态完全不同的另一棵树，是“一树多变”的总开关。

六种曲线

SpeedTree 用颜色区分不同类型的曲线。这是最容易混淆、也最值得先搞清楚的一组概念。

曲线	颜色	作用范围	说明
Parent 父级曲线	绿色	一整组节点	按子节点在父级上的位置分配数值。用于让树的不同部位表现不同——例如让树冠底部的枝条比顶部更长。可设置 Relative（相对 Boundaries）或 Absolute（相对父级绝对长度）两种求值模式。
Profile 剖面曲线	浅蓝	单个节点	沿单个节点的长度作用，同一生成器里每个节点的效果完全一致。最典型的例子是树干锥度：左端对应枝条基部，右端对应枝条末端，枝条由此从粗变细。
Distribution 分布曲线	橙色	一整组节点	控制固定数量节点的疏密分布——不改变总数，只改变聚集在哪里。例如把大部分一级枝集中到树干基部与顶部，让中段稀疏。
Pruning 修剪曲线	—	一整组节点	每个生成器仅有一条。按节点在树中的位置整批移除。曲线值低于 0.5 的位置，其节点被移除。
Resolution 分辨率曲线	—	VFX 专用	切换 Resolution（High / Medium / Low / Draft）时按曲线改变参数值。例如降低分辨率时自动减少枝条的分段数。
LOD 曲线	深蓝	LOD 属性组专用	只出现在 LOD 属性组里，控制各 LOD 属性在整段 LOD 过渡中的变化节奏。左端永远对应最高 LOD（1.0），右端对应最低 LOD（0.0）。多数情况用线性即可，让每一级简化幅度接近。

父级曲线的高级用法：Parent Level

父级曲线默认针对直接父级求值。假设一棵树有四级：Tree → Trunk → Big Branches → Little Branches。

• 想让细枝在大枝末端变小 → 不改父级层级，直接编辑长度曲线（默认行为）。
• 想让细枝在整棵树的顶部变小，而不是在大枝末端变小 → 把曲线的 Parent Level 从 Big Branches 改成 Trunk。这个设置在曲线编辑器左上角的下拉框里。
• 想同时满足两个条件 → 用复合曲线（compound curves，SpeedTree 8 起支持），在曲线编辑器里为多个父级层级分别设曲线。

曲线编辑器怎么用

1. 横轴永远是父级位置（0 = 父级根部，1 = 父级末端），不是世界坐标。
2. 在曲线上单击添加控制点，右键删除控制点。
3. 拖动控制点两侧的手柄调整切线做平滑过渡；按住 Shift 可以打断手柄做硬转折。
4. 曲线默认是两个端点连成的直线，也就是恒定值。想做出“中间密两头疏”就把中点往上拉。
5. 曲线可以存成预设复用。官方示例里就有 Uniform.png、Variance.png、Parent_Curve.png 这类曲线预设。

随机种子的分组

SpeedTree 把随机种子拆成多个独立通道，这样可以“只让枝条位置变、其它都不变”：

种子	控制什么
Random Seeds:Generation	节点生成位置、数量、朝向的随机序列。最常用。
Random Seeds:Branch	枝条形态（脊线、弯曲）的随机。
Random Seeds:Spine	脊线形状的随机。
Random Seeds:Forces	力场作用的随机。
Random Seeds:LOD	LOD 简化过程的随机。
Random Seeds:Vertex colors	顶点色噪波的随机。
Random Seeds:Welding	顶点焊接的随机。

参数搜索

Properties 面板顶部的 Search properties.. 支持按名称过滤参数。选中一个 Branch 输入 wind 就只剩风力相关项。参数多的节点（如 Branch 有近 600 个参数条目）不搜索会很难找。

A SpeedTree parameter is not just “a number.” The same parameter can be a fixed value, a curve, or a range with a random distribution. Understanding this is what makes it clear why SpeedTree trees never look repetitive.

The four parameter forms

Form	Appearance	Purpose
Scalar Value	a single number field	Every instance uses the same value, for example “branch length = 1.2”.
Curve	a small graph with draggable control points	Makes a parameter vary along the parent position or the node's length. See the next section.
Variance	a second input field next to the value	Adds a random range to the parameter. The variance algorithm can be Gaussian (concentrated at the center), Uniform (even), Blended, or Cohesive (neighboring nodes stay consistent).
Random Seed	an integer	Determines the entire random sequence. Changing one number gives a completely different tree — the master switch for “one tree, many variations”.

The six kinds of curve

SpeedTree distinguishes curve types by color. This is the most easily confused set of concepts, and the one most worth getting straight early on.

Curve	Color	Scope	Notes
Parent curve	green	a whole group of nodes	Distributes values by where the child nodes sit on the parent. Used to make different parts of the tree behave differently — for example, making branches at the bottom of the crown longer than those at the top. Evaluation can be set to Relative (relative to boundaries) or Absolute (relative to the parent's absolute length).
Profile curve	light blue	a single node	Acts along the length of a single node, and every node in the same generator is affected identically. The classic example is trunk taper: the left end corresponds to the branch base and the right end to the branch tip, so the branch tapers from thick to thin.
Distribution curve	orange	a whole group of nodes	Controls the density distribution of a fixed number of nodes — it does not change the total, only where they cluster. For example, concentrating most first-order branches at the base and the top of the trunk and leaving the middle sparse.
Pruning curve	—	a whole group of nodes	Each generator has only one. Removes nodes in bulk based on their position in the tree. Where the curve value is below 0.5, the nodes there are removed.
Resolution curve	—	VFX only	Changes parameter values along the curve when switching Resolution (High / Medium / Low / Draft). For example, automatically reducing branch segment counts at lower resolution.
LOD curve	dark blue	LOD property group only	Appears only in the LOD property group, controlling how each LOD property changes across the whole LOD transition. The left end always corresponds to the highest LOD (1.0) and the right end to the lowest (0.0). Linear is fine in most cases, so that each level simplifies by a similar amount.

Advanced parent curve usage: Parent Level

By default a parent curve evaluates against the immediate parent. Suppose a tree has four levels: Tree → Trunk → Big Branches → Little Branches.

• To make the little branches smaller at the tip of a big branch → leave the parent level alone and edit the length curve directly (the default behavior).
• To make the little branches smaller toward the top of the whole tree rather than at the tip of their big branch → change the curve's Parent Level from Big Branches to Trunk. This setting is in the drop-down at the top left of the curve editor.
• To satisfy both conditions at once → use compound curves (supported since SpeedTree 8) and set a curve for each parent level in the curve editor.

Using the curve editor

1. The X axis is always parent position (0 = base of the parent, 1 = tip of the parent), never world coordinates.
2. Click on the curve to add a control point, right-click to delete one.
3. Drag the handles on either side of a control point to adjust tangents and make smooth transitions; hold Shift to break the handles for a hard corner.
4. By default a curve is the straight line between its two endpoints, that is, a constant value. To get “dense in the middle, sparse at both ends,” pull the midpoint upward.
5. Curves can be saved as presets and reused. The official samples ship curve presets such as Uniform.png, Variance.png and Parent_Curve.png.

How random seeds are split up

SpeedTree splits the random seed into several independent channels, so you can “change only branch positions and leave everything else alone”:

Seed	What it controls
Random Seeds:Generation	The random sequence for node generation position, count and orientation. Most used.
Random Seeds:Branch	Randomness of branch form (spine, curvature).
Random Seeds:Spine	Randomness of spine shape.
Random Seeds:Forces	Randomness of force application.
Random Seeds:LOD	Randomness of the LOD simplification process.
Random Seeds:Vertex colors	Randomness of vertex color noise.
Random Seeds:Welding	Randomness of vertex welding.

Searching parameters

The Search properties.. box at the top of the Properties panel filters parameters by name. Select a Branch and type wind and only the wind-related entries remain. On parameter-heavy nodes (a Branch has nearly 600 parameter entries) this is the only practical way to find anything.

Generation 是所有生成器里参数最多、也最重要的一组。它回答一个核心问题：子节点生成多少个、长在父级的什么位置、朝哪个方向。在实测数据中，Branch 有 230 个 Generation 参数，Leaf Mesh 有 215 个，Frond 有 169 个。

Generation 参数分为两部分：所选模式独有的参数，以及所有模式共用的参数。

2.1.1　Mode：十种分布模式

模式	中文	官方说明	典型用途
Classic	经典	仅为兼容旧模型而存在，新模型应避免使用。	仅旧文件
Proportional	按比例	依据父级的尺寸创建节点，适合在父级上随机分布节点。	让长枝上自然长出更多侧枝
Proportional steps	比例阶梯	创建一系列阶梯，每级阶梯包含若干节点。这种风格常见于松树。	针叶树的轮生枝
Absolute	绝对数量	创建精确数量的节点，不随父级尺寸变化，应节制使用。常见用法是指定唯一的一根树干，或定期减少节点数。	树干上固定 5 根主枝
Absolute steps	绝对阶梯	创建精确数量的阶梯，每级若干节点。同样不适应父级尺寸，应节制使用。	—
Phyllotaxy	叶序	提供多种常见的叶片生长方式（互生 / 对生 / 轮生等）。	写实的叶片排列、松柏轮生枝
Interval	间隔	沿父级按固定间隔创建节点，适用范围很广。	棕榈叶沿树干等距分布
Bifurcation	分叉	在父级发生转折的位置放置节点，模拟枝条的分裂。官方原话："分叉往往是让模型看起来有机自然的最简单办法。"	让侧枝正好长在分叉点上
Flood	填充	创建精确数量的节点，并沿父级随机放置。	快速铺满
Parent	继承父级	创建精确数量的节点，放在父级的原点处。	让子级与父级对齐

2.1.2　共用参数：边界与分布

参数	作用
Generation:First	父级上允许生成节点的最低位置。
Generation:Last	父级上允许生成节点的最高位置。
Generation:Shared:Boundaries:Clip	移除被 Spread 或 Position 方差推出 First~Last 范围之外的节点。开启它边界才是“硬”的。
Generation:Frequency	父级曲线，控制沿父级长度方向的分布权重。默认恒为 1。
Generation:Pruning	修剪曲线。曲线值低于 0.5 的位置，节点被整批移除。
Generation:Knockout:Amount	剔除数量。在模式产生节点之后、计算之前随机移除一部分。可用父级曲线按树体结构定位。
Generation:Knockout:+Resolution	让剔除量随 Resolution 增减。
Generation:Size scalar	缩放节点及其全部子级的尺寸。
Generation:Masks	指定遮罩资源以限制节点出现位置。

2.1.3　共用参数：整体变换

参数	作用
Generation:Rotation	把该生成器的全部节点作为整体绕父级脊线旋转。配合方差可打乱朝向。
Generation:Position	把全部节点沿父级上下平移。
Generation:Sink	整体调整节点起点，使其陷入或远离父级表面。常用来把树干略微压到地面以下，便于场景摆放。

2.1.4　共用参数：Extend parent 延伸父级

这组参数用于在父级枝条末端额外生成节点，不受所选模式影响。如果 Branch 延伸另一个 Branch，两者之间会是无缝过渡——可以逐级延伸，从树干一路做到枝梢而没有接缝。Cap 生成器就是用这种方式产生的。

该功能生效的前提是：父级必须是 Branch 生成器，子级只能是 Branch、Cap、Leaf mesh 或 Batched leaf。

Type 取值	含义
None	不生成延伸节点。
Any	父级的每个开口端各生成一个节点（枝条可能分裂成两个开口）。
Split 1	从父级的第一个分裂（或唯一开口）生成。
Split 2	从父级的第二个分裂生成（如果存在）。
Skinny	从父级两个分裂中较细的那个生成。
Fat	从父级两个分裂中较粗的那个生成。
Breaks only	仅当父级断裂时才生成。
Bottom	生成一个延伸父级底部的节点。

Count 控制单个父级上最多能挂几个延伸节点，通常设为 1。多个生成器可以延伸同一个父级——配合分裂相关的取值（Split 1/2、Skinny/Fat）可以分别定位分裂后的每一部分。

2.1.5　共用参数：力容器与网格对齐

参数组	作用
Force containers: Include	只有落在指定几何力场内部的节点才会被创建。
Force containers: Exclude	落在指定几何力场内部的节点不会被创建。
Mesh alignment	把网格对齐到指定方向。仅对 Leaf mesh / Batched leaf 以及点击放置产生的节点有效，且父级必须是网格。可选 None / Tangent / Binormal / Parent X,Y,Z / World X,Y,Z。
Click place	控制该生成器如何响应自由手绘模式下的点击放置操作：Ready（接受任意）、None（不接受）、Any（优先接受）、Number（只接受对应 ID）。

2.1.6　Active 与 Resolution 联动

Generation:Shared:Active 是一条按分辨率开关生成器的曲线：曲线值大于 0.5 时该生成器启用，小于 0.5 时关闭。

用它可以在不同分辨率下整批替换生成器。官方给的例子很典型：

• 做一份叶片贴图，在 Draft 和 Low 分辨率下只启用一片叶子；
• 在 Medium 和 High 分辨率下启用五片叶子的版本。

这样同一个模型就能自动适应不同的质量等级，而不需要维护多个文件。

Generation is the largest and most important parameter group on any generator. It answers one core question: how many child nodes are generated, where on the parent they sit, and which way they point. In measured data a Branch has 230 Generation parameters, a Leaf Mesh 215 and a Frond 169.

Generation parameters fall into two parts: the parameters unique to the selected mode, and the parameters shared by every mode.

2.1.1　Mode: ten distribution modes

Mode	Plain meaning	Official description	Typical use
Classic	classic	Exists only for compatibility with older models; new models should avoid it.	old files only
Proportional	by proportion	Creates nodes based on the parent's size; good for distributing nodes randomly over a parent.	Let long branches naturally grow more side branches
Proportional steps	proportional steps	Creates a series of steps, each containing several nodes. This style is common on pines.	Whorled branches on conifers
Absolute	absolute count	Creates an exact number of nodes, independent of parent size; use it sparingly. Typical uses are specifying a single trunk, or periodically reducing the node count.	A fixed 5 primary branches on a trunk
Absolute steps	absolute steps	Creates an exact number of steps, each with several nodes. It likewise does not adapt to parent size and should be used sparingly.	—
Phyllotaxy	leaf arrangement	Provides several common leaf growth patterns (alternate / opposite / whorled and so on).	Realistic leaf arrangement, whorled conifer branches
Interval	interval	Creates nodes at a fixed spacing along the parent, and applies very broadly.	Palm fronds evenly spaced along the trunk
Bifurcation	forking	Places nodes at the points where the parent turns, simulating how branches split. In the words of the documentation: “Bifurcation is often the simplest way to make a model look organically natural.”	Side branches landing exactly on fork points
Flood	flood	Creates an exact number of nodes and places them randomly along the parent.	Fast coverage
Parent	inherit from parent	Creates an exact number of nodes at the parent's origin.	Align children with the parent

2.1.2　Shared parameters: boundaries and distribution

Parameter	Purpose
Generation:First	The lowest position on the parent where nodes may be generated.
Generation:Last	The highest position on the parent where nodes may be generated.
Generation:Shared:Boundaries:Clip	Removes nodes pushed outside the First–Last range by Spread or Position variance. Only with this enabled are the boundaries “hard”.
Generation:Frequency	A parent curve controlling the distribution weight along the parent's length. Constant 1 by default.
Generation:Pruning	Pruning curve. Where the curve value is below 0.5, the nodes there are removed in bulk.
Generation:Knockout:Amount	Knockout amount. Randomly removes a portion after the mode has produced the nodes but before evaluation. It can be positioned by tree structure using a parent curve.
Generation:Knockout:+Resolution	Makes the knockout amount increase or decrease with Resolution.
Generation:Size scalar	Scales the size of a node and all of its children.
Generation:Masks	Specifies mask assets to restrict where nodes may appear.

2.1.3　Shared parameters: overall transforms

Parameter	Purpose
Generation:Rotation	Rotates all of the generator's nodes as a group around the parent spine. Add variance to scramble the orientation.
Generation:Position	Translates all nodes up or down along the parent.
Generation:Sink	Adjusts node origins as a group so that they sink into or pull away from the parent's surface. Commonly used to push the trunk slightly below ground level for easier scene placement.

2.1.4　Shared parameters: Extend parent

This group generates extra nodes at the tip of the parent branch, independently of the selected mode. If a Branch extends another Branch, the transition between them is seamless — you can extend level by level from the trunk all the way out to the twigs with no seams. This is how Cap generators are produced.

The feature requires that the parent is a Branch generator and the child is only a Branch, Cap, Leaf mesh or Batched leaf.

Type value	Meaning
None	No extension node is generated.
Any	Generates one node at each open end of the parent (a branch can split into two openings).
Split 1	Generates from the parent's first split (or its only opening).
Split 2	Generates from the parent's second split, if it exists.
Skinny	Generates from the thinner of the parent's two splits.
Fat	Generates from the thicker of the parent's two splits.
Breaks only	Generates only when the parent is broken.
Bottom	Generates a node extending the bottom of the parent.

Count controls how many extension nodes can hang on a single parent; it is usually set to 1. Several generators can extend the same parent — together with the split-related values (Split 1/2, Skinny/Fat) you can address each part of a split separately.

2.1.5　Shared parameters: force containers and mesh alignment

Parameter group	Purpose
Force containers: Include	Only nodes that fall inside the specified geometry force are created.
Force containers: Exclude	Nodes that fall inside the specified geometry force are not created.
Mesh alignment	Aligns the mesh to a specified direction. Only effective for Leaf mesh / Batched leaf and for nodes produced by click placement, and the parent must be a mesh. The options are None / Tangent / Binormal / Parent X,Y,Z / World X,Y,Z.
Click place	Controls how the generator responds to click placement in freehand mode: Ready (accepts any), None (accepts none), Any (takes priority), Number (only accepts the matching ID).

2.1.6　Active linked to Resolution

Generation:Shared:Active is a curve that switches a generator on and off by resolution: when the curve value is above 0.5 the generator is enabled, and below 0.5 it is disabled.

You can use it to swap whole generators at different resolutions. The official example is a good one:

• Make one leaf texture and enable a single leaf at Draft and Low resolution;
• enable the five-leaf version at Medium and High resolution.

That way a single model automatically adapts to different quality tiers without maintaining several files.

每个 Branch 内部都有一条脊线（Spine）——它是枝条的中心线。几何体是沿着这条线“扫”出来的，所以脊线的形状就决定了枝条的形状。Branch 节点有 70 个 Spine 参数，是仅次于 Generation 的第二大参数组。

核心参数

参数	作用	取值范围与经验
Spine:Length	枝条长度，相对父级长度的比例。	0～1 之间是“比父级短”，>1 是“比父级长”。主枝常用 0.3～0.6。
Spine:Style	脊线形态风格。	不同风格对应不同的弯曲模板。
Spine:Shape	形状曲线。X = 沿脊线 0～1，Y = 横向偏移量。	这是最常用的参数。把曲线拉成一个弧形，枝条就会自然弯曲。直线看起来一定假，真实枝条都有弧度。
Spine:Droop	下垂。模拟重力让枝条末端往下垂。	柳树、棕榈需要较大的下垂值；松树几乎不需要。
Spine:Jink	折角。制造不规则的硬转折。	小幅值（0.05～0.15）能有效打破“太顺滑”的假感。
Spine:Noise	噪波。给脊线叠加随机扰动。	让枝条表面走向略微抖动，近景看更真实。
Spine:Orientation	脊线朝向。	控制弯曲朝向哪一侧。
Spine:Path	路径。手绘模式下可自定义走向。	用于藤蔓、根系等自由走向结构。
Spine:Prune	脊线修剪。	—
Spine:Break	断裂。模拟枝条折断。	做枯木、断枝时使用。
Spine:Match parent	与父级匹配。	让子枝的弯曲延续父级的趋势。

Spine 与 Forces 的分工

这两组参数都能让枝条弯曲，但机制不同：

• Spine:Shape 是内在的——它直接定义这根枝条本身长成什么形状。
• Forces 是外在的——它模拟外力（重力、风、遮挡物）对枝条的影响，作用范围可以跨层级。

实操建议：先用 Spine:Shape 定基本弧线，再用 Forces 做整体协调。只用 Spine 会显得每根枝条各长各的；只用 Forces 则难以精确控制单根枝条的造型。

Every Branch has a spine inside it — the centerline of the branch. The geometry is swept along that line, so the spine's shape determines the branch's shape. A Branch node has 70 Spine parameters, making it the second-largest group after Generation.

Core parameters

Parameter	Purpose	Range and experience
Spine:Length	Branch length as a proportion of the parent's length.	Between 0 and 1 means shorter than the parent; >1 means longer. Primary branches usually 0.3–0.6.
Spine:Style	Spine form style.	Different styles correspond to different curvature templates.
Spine:Shape	Shape curve. X = 0–1 along the spine, Y = lateral offset.	The most-used parameter. Pull the curve into an arc and the branch bends naturally. A straight line always looks fake; real branches have curvature.
Spine:Droop	Droop. Simulates gravity pulling the branch tip down.	Willows and palms need a large droop value; pines need almost none.
Spine:Jink	Jink. Creates irregular hard corners.	A small value (0.05–0.15) effectively breaks the “too smooth” fake look.
Spine:Noise	Noise. Adds random perturbation to the spine.	Makes the branch direction wobble slightly, which reads better up close.
Spine:Orientation	Spine orientation.	Controls which side the curvature bends toward.
Spine:Path	Path. A custom path in freehand mode.	For vines, roots and other free-form structures.
Spine:Prune	Spine pruning.	—
Spine:Break	Break. Simulates a snapped branch.	For dead wood and broken branches.
Spine:Match parent	Match parent.	Makes a child branch's curvature continue the parent's trend.

How Spine and Forces divide the work

Both groups can bend a branch, but the mechanism differs:

• Spine:Shape is intrinsic — it directly defines the shape this branch grows into.
• Forces is extrinsic — it simulates outside influences (gravity, wind, obstacles) on the branch, and its reach can cross levels.

Practical advice: use Spine:Shape first to set the basic arc, then use Forces for overall coherence. Spine alone makes every branch look like it grew in isolation; Forces alone makes it hard to precisely control any single branch.

Generation 和 Spine 决定形态，Segments 决定形态用什么精度表达出来。这组参数直接对应面数，是性能优化的主战场。

参数	作用	经验值
Segments:Length	沿枝条长度方向的分段数。	树干 8–16；主枝 4–8；细枝 2–4。段数不足时弯曲会变成折线。
Segments:Radial	横截面圆周分段数。	树干 8–12；主枝 6–8；细枝 3–4。低于 5 会明显看出多边形棱角。
Segments:Resolution	总体网格分辨率，是 Length 与 Radial 的总控。	调这个比分别调上面两个更快。
Segments:Scalar	分段缩放系数。	—
Segments:Accuracy	几何精度。	提高会让曲面更精确，代价是面数。
Segments:Features	特征保留。	简化时保留哪些几何特征。
Segments:Influence	影响范围。	—
Segments:Painted Vertices	顶点绘制相关的分段。	与手绘编辑配合。

面数怎么算

一根枝条的三角面数大致为：

面数 ≈ (Length 段数) × (Radial 段数) × 2

举例：Length=10、Radial=8 的一根枝条 ≈ 10 × 8 × 2 = 160 个三角面。如果这棵树有 200 根这样的枝条，就是 32,000 面——已经接近一棵游戏用中等树的全部预算。

Segments 也会随 LOD 变化

枝条与羽叶可以随 LOD 改变分段数——即使这个枝条本身保留在树里，也能降低它的几何复杂度。可以分别显式设置长度分段与圆周分段，也可以调整 Optimization 属性，让 Modeler 智能决定在哪里减段而尽量保持整体形状。

Generation and Spine decide the form; Segments decides at what precision that form is expressed. This group maps directly to polygon count and is the main battleground for performance optimization.

Parameter	Purpose	Rule of thumb
Segments:Length	Number of segments along the branch's length.	Trunk 8–16; primary branches 4–8; twigs 2–4. Too few segments turns curvature into visible facets.
Segments:Radial	Number of segments around the cross-section.	Trunk 8–12; primary branches 6–8; twigs 3–4. Below 5 you clearly see polygonal edges.
Segments:Resolution	Overall mesh resolution — the master control over Length and Radial.	Faster to adjust than the two above separately.
Segments:Scalar	Segment scale factor.	—
Segments:Accuracy	Geometry accuracy.	Higher makes curved surfaces more precise at the cost of polygons.
Segments:Features	Feature preservation.	Which geometric features to keep when simplifying.
Segments:Influence	Influence range.	—
Segments:Painted Vertices	Segments related to vertex painting.	Works together with freehand editing.

How to estimate polygon count

The triangle count of a single branch is roughly:

triangles ≈ (Length segments) × (Radial segments) × 2

For example, a branch with Length=10 and Radial=8 is ≈ 10 × 8 × 2 = 160 triangles. If the tree has 200 such branches, that is 32,000 triangles — already close to the entire budget of a mid-range game tree.

Segments change with LOD too

Branches and fronds can change their segment counts with LOD — even when the branch itself is kept in the tree, its geometric complexity can be reduced. You can set length segments and radial segments explicitly, or adjust the Optimization property to let the Modeler decide intelligently where to drop segments while preserving the overall shape as far as possible.

Forces 是让 SpeedTree 的树“看起来是真的”的关键。程序化生成最大的毛病是太规整：枝条均匀分布、笔直生长、互不相交。力场通过模拟外力来打破这种规整。

在实测数据中，Branch 有 56 个 Forces 参数，是所有生成器里最多的。下面是 v10.2.0 里实际存在的力场类型：

力场	中文	作用
Forces:Gnarl	扭曲力	最重要的一个。让枝条产生不规则的扭动。真实树木因为生长竞争、虫害、风向，几乎不会笔直。建议从 0.1～0.3 开始试。
Forces:Twist	扭转力	沿枝条自身轴旋转，让枝干表面纹理跟着扭，增加动势。
Forces:Direction	方向力	把枝条往一个固定方向推。用来表现常年单向风造成的“旗形树冠”。
Forces:Gravity	重力	让枝条下垂。与 Spine:Droop 的区别是它作用于整个子树。
Forces:Curl	卷曲力	让枝条末端卷起来。蕨类、卷须常用。
Forces:Repel	排斥力	避免穿插的利器。让节点之间互相推开。枝叶穿模是程序化树的常见问题，开这个能大幅缓解。
Forces:Repulse	脉冲排斥	排斥的变体。
Forces:Attraction	吸引力	把枝条吸向某处。
Forces:Magnet	磁力	把枝条吸附到指定对象上。
Forces:Mesh / Mesh 2 / Mesh 3	网格力	让枝条沿着一个外部模型的表面生长。做爬墙藤蔓、依附岩石的根系时必用。官方示例 samples/Learning/Forces/Mesh_Crawling_on_Tree.spm 就是演示这个。
Forces:Obstruction	障碍力	让枝条绕开碰撞体生长，模拟被建筑/岩石挡住。
Forces:Planar	平面力	把枝条压向一个平面，做“贴墙生长”的藤蔓。
Forces:Return	回归力	把偏离太远的枝条拉回来，防止被其它力推飞。
Forces:Vine / Small Vines / Big Vine / Vines	藤蔓力	藤蔓专用力场组。
Forces:Roots / BigRoots	根系力	根系生长专用。
Forces:Trunk	树干力	—
Forces:Flooring	落地力	让枝条不会穿到地面以下。
Forces:Align	对齐力	让枝条趋向某个共同方向。
Forces:General Direction	总体方向	全局方向控制。
Forces:Bounce on me!	弹性碰撞	开启后被其它节点碰撞时会回弹。名字很随意，但确实是官方参数名。
Forces:Allow forces	允许力场	总开关。关掉后该节点完全不受任何力场影响。排查“为什么调了力场没反应”时先看这里。

力场的作用范围

力场挂在哪个节点上，就影响该节点及其所有子孙。所以：

• 想让整棵树都受某个力影响 → 挂在树干上。
• 只想让末梢细枝乱一点 → 挂在最末一级 Branch 上。
• 多个力场可以叠加，效果是相加的。

官方力场示例

安装目录 samples/Learning/Forces/ 下有完整的力场演示文件，建议逐个打开研究：

文件	演示内容
Attenuation.spm	力场衰减
Bounce.spm	弹性碰撞
Geometry_Force.spm	几何体力场
Mesh_Crawling_on_Mesh.spm	网格在网格上爬行
Mesh_Crawling_on_Tree.spm	网格在树上爬行

这些示例配套了 box.obj、sphere.obj、torus.obj、dica.obj、rook.FBX 等参考模型，可以直接看到力场如何把枝条“推”到模型表面上。

Forces is what makes SpeedTree trees look real. The biggest problem with procedural generation is that it is too regular: branches evenly spaced, growing perfectly straight, never intersecting. Forces break that regularity by simulating outside influences.

In measured data a Branch has 56 Forces parameters — more than any other generator. These are the force types actually present in v10.2.0:

Force	Plain meaning	Purpose
Forces:Gnarl	gnarl	The most important one. Gives branches irregular twisting. Real trees are almost never straight, thanks to growth competition, pests and prevailing wind. Start around 0.1–0.3.
Forces:Twist	twist	Rotates along the branch's own axis so the surface texture twists with it, adding a sense of movement.
Forces:Direction	directional force	Pushes branches in one fixed direction. Used for the “flag-shaped crown” caused by constant one-way wind.
Forces:Gravity	gravity	Pulls branches down. Unlike Spine:Droop, it acts on the whole subtree.
Forces:Curl	curl	Curls branch tips. Common on ferns and tendrils.
Forces:Repel	repulsion	A great anti-intersection tool. Pushes nodes apart. Intersecting foliage is a common procedural tree problem and this greatly reduces it.
Forces:Repulse	repulse	A variant of repulsion.
Forces:Attraction	attraction	Pulls branches toward a point.
Forces:Magnet	magnet	Snaps branches onto a specified object.
Forces:Mesh / Mesh 2 / Mesh 3	mesh force	Makes branches grow along the surface of an external model. Essential for vines crawling up walls or roots clinging to rocks. The official sample samples/Learning/Forces/Mesh_Crawling_on_Tree.spm demonstrates this.
Forces:Obstruction	obstruction	Makes branches grow around collision bodies, simulating being blocked by buildings or rocks.
Forces:Planar	planar	Flattens branches toward a plane, for vines that “hug a wall”.
Forces:Return	return	Pulls branches that have strayed too far back in, so the other forces do not fling them away.
Forces:Vine / Small Vines / Big Vine / Vines	vine forces	A force group dedicated to vines.
Forces:Roots / BigRoots	root forces	Dedicated to root growth.
Forces:Trunk	trunk force	—
Forces:Flooring	flooring	Keeps branches from passing below the ground plane.
Forces:Align	align	Makes branches converge on a common direction.
Forces:General Direction	general direction	Global direction control.
Forces:Bounce on me!	bounce	When on, the node bounces off collisions with other nodes. The name is casual, but it really is the official parameter name.
Forces:Allow forces	allow forces	The master switch. When off, the node is completely unaffected by any force. Check here first when wondering “why does my force do nothing”.

The reach of a force

A force affects the node it sits on plus all of that node's descendants. So:

• To affect the whole tree, put it on the trunk.
• To roughen only the tip twigs, put it on the last Branch level.
• Multiple forces stack, and their effects add together.

Official force samples

The install directory samples/Learning/Forces/ contains complete force demo files; open them one by one and study them:

File	What it demonstrates
Attenuation.spm	force attenuation
Bounce.spm	bounce collisions
Geometry_Force.spm	geometry force
Mesh_Crawling_on_Mesh.spm	a mesh crawling on a mesh
Mesh_Crawling_on_Tree.spm	a mesh crawling on a tree

These samples come with reference models such as box.obj, sphere.obj, torus.obj, dica.obj and rook.FBX, so you can see exactly how a force “pushes” branches onto a model's surface.

SpeedTree 的风力不是“给模型加一段动画”，而是把风力参数烘焙进顶点数据，导出后由引擎的 SpeedTree 运行时实时计算摆动。这样做的好处是文件小、效果可控、引擎开销低。

风力参数

参数	作用
Wind:Apply	总开关。关掉后该节点不参与风动。
Wind:Weight	风力权重，最核心的参数。0 = 完全不动，1 = 完全随风摆。
Wind:Inherited weight scale	子节点从父级继承的权重倍率。用于让末梢比父级摆得更厉害。
Wind:Offset	相位偏移。让不同的枝不同步摆动，否则整棵树会像一块板子一样晃。
Wind:Level offset	层级偏移。按节点层级自动错开相位。
Wind:Rotation	旋转响应。枝条绕自身轴的扭转响应。

权重分配原则

真实的树在风中：树干几乎不动，主枝轻微摇，细枝和叶片剧烈抖。所以权重应该沿层级递增：

节点	建议 Wind:Weight
树干（Level 1）	0.02 – 0.08
主枝（Level 2）	0.10 – 0.20
侧枝（Level 3）	0.25 – 0.45
末梢细枝（Level 4+）	0.5 – 0.7
叶片 / 羽叶	0.7 – 1.0

先跑一遍 Wind wizard

官方文档在讲风力时，反复给出的推荐做法只有一条：先用 Tools 菜单里的 Wind wizard（风力向导）跑一遍，再手工微调。向导会自动按层级分配合理的权重，比从零手调快得多，也更容易得到自然的结果。

只有一两个层级会独立摆动

这是风力系统里最容易被误解、也最容易调不出效果的地方：

• 风动是否"独立"，取决于从 Tree 出发、沿着任意路径遇到的第一个启用了 Wind:Apply 的生成器。是这个生成器决定了独立运动的归属，而不是你最后调的那个。
• 系统只给一到两个枝条层级独立运动。所以应该把独立运动分配给从树干分出的粗大主枝，而几乎不要给树干本身。
• 如果层级选错了，就会出现"调了半天没反应"或者"整棵树一起晃"的现象。

运动速度的层级关系

Shared Motion（整体运动）  <  Branch Motion（枝条运动）  <  Leaf Motion（叶片运动）
      慢、幅度大                    中                              快、幅度小

三者叠加才有真实感。另外 Wind:Independence 的典型取值区间是大于 1.0、小于 10.0。

Fan 对象与解剖学权重

所有风力属性都挂在一个叫 Fan 的场景对象上，而不是散落在各个生成器里。Fan 的 Actions 菜单里有一个 Set anatomical weights（设置解剖学权重），可以一次性按植物解剖结构分配好权重，是手工调参之外最快的办法。

v10.2.0 里风力按目标引擎分成几组独立算法，因为它们实现方式不同，参数并不通用——见下一节。

导出到 UE 时的风力

• 用 .st9 格式导入 UE 时，风力是在材质里用 GPU 计算的，材质上没有强度参数。所以风力强度必须在 SpeedTree Modeler 里先调好再导出。
• 一棵树如果有多个材质实例，必须把所有实例改成同一组数值，否则同一棵树的各部分会以不同幅度摆动，出现"分离"现象。

引擎侧的风力参数组

v10.2.0 里风力参数按目标引擎分成了几组，因为不同引擎的运行时实现不同：

参数组	目标
Wind:Games	游戏引擎通用风力参数
Wind:VFX	影视级风力参数（更细腻，可烘焙）
Wind:Legacy UE4/Unity	旧版 UE4 / Unity 兼容参数
Wind:Lumberyard	Amazon Lumberyard 引擎兼容参数

风力的两套体系：Shared Motion 与 Ripple Motion

在参数表里还能看到这几组（出现在导出与运行时的配置里）：

• Games Shared Motion / SDK Shared Motion / Global Motion —— 整体运动。整棵树作为一个整体被风吹动，幅度大、频率低。
• Games Ripple Motion / SDK Ripple Motion —— 涟漪运动。叶片层面的高频抖动，幅度小、频率高。

两者叠加才有真实感：整体慢慢摇 + 叶片快速抖。渲染模式里的 _Wind Weights/Level 1.fx ～ Level 4.fx 和 Ripple.fx 就是用来分别查看这两套权重的。

风力相关的导出预设

export_presets/VFX/Wind.ini 是专门用于烘焙风力动画的预设，输出的是可被渲染器直接使用的风力数据，而不是游戏运行时的顶点属性。

SpeedTree's wind is not “an animation added to the model” — it bakes wind parameters into the vertex data, and after export the engine's SpeedTree runtime computes the swaying in real time. The payoff is small files, controllable results and low engine cost.

Wind parameters

Parameter	Purpose
Wind:Apply	Master switch. When off, the node takes no part in wind motion.
Wind:Weight	Wind weight, the core parameter. 0 = completely still, 1 = fully swaying with the wind.
Wind:Inherited weight scale	Multiplier for the weight a child inherits from its parent. Used to make tips sway harder than their parents.
Wind:Offset	Phase offset. Makes different branches sway out of sync; otherwise the whole tree rocks like a single board.
Wind:Level offset	Level offset. Automatically staggers phase by node level.
Wind:Rotation	Rotation response — the twist response of a branch about its own axis.

How to distribute weight

A real tree in wind: the trunk barely moves, primary branches sway slightly, twigs and leaves shake violently. So weight should increase with level:

Node	Suggested Wind:Weight
Trunk (Level 1)	0.02 – 0.08
Primary branches (Level 2)	0.10 – 0.20
Secondary branches (Level 3)	0.25 – 0.45
Tip twigs (Level 4+)	0.5 – 0.7
Leaves / fronds	0.7 – 1.0

Run the Wind wizard first

When the official documentation discusses wind, the one recommendation it repeats is: run the Wind wizard from the Tools menu first, then fine-tune by hand. The wizard assigns sensible weights by level automatically, which is much faster than hand-tuning from scratch and more likely to look natural.

Only one or two levels sway independently

This is the most misunderstood part of the wind system, and the most common reason wind “does not work”:

• Whether motion is “independent” depends on the first generator with Wind:Apply enabled that you meet walking down from the Tree along any path. That generator determines what owns the independent motion — not the last one you edited.
• The system gives independent motion to only one or two branch levels. So assign it to the thick primary branches coming off the trunk, and almost never to the trunk itself.
• Pick the wrong level and you get either “I tuned it for ages and nothing happens” or “the whole tree rocks as one piece”.

The level relationship of motion speeds

Shared Motion (whole tree)  <  Branch Motion (branches)  <  Leaf Motion (leaves)
       slow, large amplitude              medium                   fast, small amplitude

Only the three layered together feel real. Also, the typical range for Wind:Independence is greater than 1.0 and less than 10.0.

The Fan object and anatomical weights

All wind properties live on a scene object called Fan rather than being scattered across the individual generators. The Fan's Actions menu contains Set anatomical weights, which assigns sensible weights for the plant's anatomy in one go — the fastest option short of hand-tuning.

In v10.2.0 wind is split into several independent algorithm groups by target engine, because their implementations differ and the parameters are not interchangeable — see the next section.

Wind when exporting to UE

• When importing into UE with the .st9 format, wind is computed on the GPU inside the material, and the material has no strength parameter. So wind strength must be dialed in inside SpeedTree Modeler before export.
• If a tree has multiple material instances, all of them must use the same set of values, or different parts of the same tree sway by different amounts and visibly “come apart”.

Engine-specific wind parameter groups

In v10.2.0 the wind parameters are split into groups by target engine, because the runtimes differ:

Parameter group	Target
Wind:Games	generic game-engine wind parameters
Wind:VFX	film-grade wind parameters (finer, bakeable)
Wind:Legacy UE4/Unity	compatibility parameters for older UE4 / Unity
Wind:Lumberyard	compatibility parameters for Amazon Lumberyard

The two wind systems: Shared Motion and Ripple Motion

The parameter tables also show these groups (they appear in export and runtime configuration):

• Games Shared Motion / SDK Shared Motion / Global Motion — shared motion. The whole tree is moved as one by the wind: large amplitude, low frequency.
• Games Ripple Motion / SDK Ripple Motion — ripple motion. High-frequency shaking at the leaf level: small amplitude, high frequency.

Only together do they feel real: the whole tree sways slowly while the leaves shake quickly. The _Wind Weights/Level 1.fx … Level 4.fx and Ripple.fx render modes exist to inspect these two weight sets separately.

Wind-related export presets

export_presets/VFX/Wind.ini is the preset dedicated to baking wind animation. It outputs wind data that a renderer can consume directly, rather than the vertex attributes a game runtime uses.

SpeedTree 的材质是一组贴图通道的集合。理解每个通道存什么，是做出高质量植被的前提。

贴图通道一览

通道	参数名	内容	说明
Color	Material:Color	基础色 / 反照率	树皮与叶片的固有颜色。
Normal	Material:Normal	法线	表面的凹凸细节。树皮几乎全靠它。
Height	Material:Height	高度	用于视差映射，制造“深进去”的立体感。
AO	Material:AO	环境光遮蔽	加深缝隙的阴影，让树皮裂缝更明显。
Opacity	Material:Opacity	不透明度	叶片必需。靠它把方形卡片抠出叶子形状。
Gloss	Material:Gloss	光泽度	决定高光的锐利程度。嫩叶比老叶亮。
Specular	Material:Specular	高光强度	—
Metallic	Material:Metallic	金属度	植物一般是 0，但可用于特殊效果。
Subsurface	Material:Subsurface	次表面颜色	叶片背光透出的颜色，通常是偏黄绿的暖色。
Subsurface Amount	Material:Subsurface Amount	次表面强度	让叶片“透光”的关键。没有它叶子会像塑料片。
Custom / Custom2	Material:Custom / Custom2	自定义通道	可用于存额外的遮罩、变化贴图等。
Vertex Displacement	Material:Vertex Displacement	顶点置换	真正推动网格顶点，做树皮的物理起伏。区别于法线贴图（只影响光照）。

贴图打包（Texture Packing）

导出时 SpeedTree 会把多个通道合并到同一张贴图的 RGBA 通道里，减少贴图数量。v10.2.0 内置了这些打包方案：

方案	Texture0	Texture1	Texture2
Standard	_Color	_Normal	_SS（次表面）
UnrealEngine	_Color（Alpha 通道存不透明度）	_Normal	_Subsurface
Unity	Unity 专用打包
Lumberyard	Lumberyard 专用打包
Unpacked	不打包，每个通道单独一张图（便于后期处理）

UE 方案的 MipGenerationFlag="AlphaIsOpacity" 表示：生成 Mipmap 时，Alpha 通道要按“不透明度”规则处理（避免叶片边缘在远处变黑）。这是 UE 植被常见的坑，SpeedTree 已经在打包配置里处理好了。

顶点属性打包（Vertex Packing）

导出时顶点数据也会被压缩。以下是 v10.2.0 的真实顶点布局：

Standard（常规模型）：

Attribute 1  half  x4   position(3) / texcoord_u(1)
Attribute 2  half  x4   lod_position(3) / texcoord_v(1)
Attribute 3  ubyte x4   normal(1) / binormal(1) / tangent(1) / ao(1)
Attribute 4  ubyte x4   wind_branch1_weight(1) / wind_branch1_dir(1) / wind_branch1_offset(1) / wind_ripple(1)
Attribute 5  ubyte x4   wind_branch2_weight(1) / wind_branch2_dir(1) / wind_branch2_offset(1) / blend(1)

可以看到：法线、副法线、切线、AO 各占 1 字节；风力权重、方向、相位偏移、涟漪各占 1 字节。整棵树的风动信息只用了 2 个 32 位字——这是 SpeedTree 高效的原因。

Standard_Billboard（公告板）：只有 2 个属性，把法线拆到位置和 UV 的剩余位里，极度压缩。

Standard_Grass（草）：4 个属性，其中 blend_and_ao_packed 把混合与 AO 压进同一个字节。草的数量极大，所以压缩更激进。

混合遮罩（Blend Masks）

安装目录 blend_masks/standard/ 提供了官方混合遮罩，用于两张贴图之间的过渡：

遮罩	适用
Default_1 / Default_2	通用
Blend_1 / Blend_2	平滑过渡
Chunky_1 / Chunky_2	块状过渡，适合树皮的斑驳
Mottled_1 / Mottled_2	斑点状，适合苔藓
Palm_1 / Palm_2	棕榈专用
Pine_1	松树专用

也可以把自己做的遮罩放进 blend_masks/custom/ 目录。

A SpeedTree material is a collection of texture channels. Understanding what each channel stores is a prerequisite for good vegetation.

Texture channels at a glance

Channel	Parameter name	Content	Notes
Color	Material:Color	base color / albedo	the intrinsic color of bark and leaves.
Normal	Material:Normal	normal	surface bump detail. Bark relies almost entirely on this.
Height	Material:Height	height	used for parallax mapping to create a sense of depth.
AO	Material:AO	ambient occlusion	deepens shadow in crevices so bark cracks read more strongly.
Opacity	Material:Opacity	opacity	required for leaves. It is what cuts a leaf shape out of a square card.
Gloss	Material:Gloss	glossiness	how sharp the specular highlight is. Young leaves are glossier than old ones.
Specular	Material:Specular	specular intensity	—
Metallic	Material:Metallic	metallic	usually 0 for plants, but usable for special effects.
Subsurface	Material:Subsurface	subsurface color	the color transmitted through a backlit leaf, usually a warm yellow-green.
Subsurface Amount	Material:Subsurface Amount	subsurface strength	the key to translucent leaves. Without it leaves look like plastic sheets.
Custom / Custom2	Material:Custom / Custom2	custom channels	for storing extra masks, variation maps and so on.
Vertex Displacement	Material:Vertex Displacement	vertex displacement	actually moves mesh vertices for physical bark relief, as opposed to a normal map, which only affects lighting.

Texture packing

At export, SpeedTree merges several channels into the RGBA channels of a single texture to reduce texture count. v10.2.0 ships these packing schemes:

Scheme	Texture0	Texture1	Texture2
Standard	_Color	_Normal	_SS (subsurface)
UnrealEngine	_Color (alpha channel holds opacity)	_Normal	_Subsurface
Unity	Unity-specific packing
Lumberyard	Lumberyard-specific packing
Unpacked	no packing; each channel gets its own map (handy for post-processing)

The UE scheme's MipGenerationFlag="AlphaIsOpacity" means: when generating mipmaps, the alpha channel must be treated as opacity (so leaf edges do not darken at distance). This is a classic UE vegetation pitfall, and SpeedTree already handles it in the packing configuration.

Vertex packing

Vertex data is compressed at export too. These are the real vertex layouts in v10.2.0:

Standard (regular models):

Attribute 1  half  x4   position(3) / texcoord_u(1)
Attribute 2  half  x4   lod_position(3) / texcoord_v(1)
Attribute 3  ubyte x4   normal(1) / binormal(1) / tangent(1) / ao(1)
Attribute 4  ubyte x4   wind_branch1_weight(1) / wind_branch1_dir(1) / wind_branch1_offset(1) / wind_ripple(1)
Attribute 5  ubyte x4   wind_branch2_weight(1) / wind_branch2_dir(1) / wind_branch2_offset(1) / blend(1)

As you can see: normal, binormal, tangent and AO each take 1 byte; wind weight, direction, phase offset and ripple each take 1 byte. The wind data for the whole tree uses only two 32-bit words — this is why SpeedTree is so efficient.

Standard_Billboard: only 2 attributes, with the normals folded into the spare bits of position and UV — extremely compressed.

Standard_Grass: 4 attributes, where blend_and_ao_packed squeezes blend and AO into the same byte. Grass appears in enormous quantities, so the compression is more aggressive.

Blend masks

The install directory blend_masks/standard/ provides official blend masks for transitions between two textures:

Mask	Use
Default_1 / Default_2	general purpose
Blend_1 / Blend_2	smooth transitions
Chunky_1 / Chunky_2	chunky transitions, good for mottled bark
Mottled_1 / Mottled_2	speckled, good for moss
Palm_1 / Palm_2	palm-specific
Pine_1	pine-specific

You can also drop your own masks into blend_masks/custom/.

Displacement 让枝条表面产生真实的几何起伏，是“近景看起来像树皮”的关键。

参数	作用
Displacement:Amount	置换总强度。最常用的旋钮。
Displacement:Source	置换源贴图。通常用高度图或专门的置换图。
Displacement:Shape	置换形状。
Displacement:Fine	细节强度。叠加高频小起伏。
Displacement:Flares	根部扩张（根盘）。让树干入土处自然变粗。做单株特写时非常有效。
Displacement:Length amount	沿长度方向的置换量。
Displacement:Sharpness	锐度。控制置换边缘的硬软。
Displacement:Mapping	贴图映射方式。
Displacement:U scale / V scale	贴图在 U/V 方向的缩放。
Displacement:Seed	随机种子，换一个就是不同的凹凸分布。
Displacement:Feature Exaggeration	特征夸张。把已有的凹凸特征放大。

UV Mapping

参数	作用
UV Mapping:Style	UV 展开方式。不同方式决定了树皮纹理怎么绕在枝条上。
UV Mapping:U / V	U/V 方向的平铺次数。U 控制纹理绕圆周重复几次，V 控制沿长度重复几次。
UV Mapping:Tiling	平铺设置总控。
UV Mapping:Create seams	是否创建 UV 接缝。做贴图绘制时需要接缝来展开。
UV Mapping:Seams seed	接缝位置的随机种子。

检查 UV 与纹素密度

渲染模式里有两个专门用来检查 UV 的：

• Texcoord.fx —— 直接显示 UV 坐标（红绿渐变），能一眼看出 UV 有没有翻转、拉伸。
• Texcoord_Seams.fx —— 高亮 UV 接缝位置。
• Texel_Density.fx —— 纹素密度检查。用颜色显示每个区域的贴图精度是否一致。树干和细枝如果纹素密度差太多，同一张贴图在细枝上会糊掉。做游戏资产时这一步必查。

Displacement gives branch surfaces real geometric relief — the key to bark that holds up in close-ups.

Parameter	Purpose
Displacement:Amount	Overall displacement strength. The most-used knob.
Displacement:Source	Source displacement texture. Usually a height map or a dedicated displacement map.
Displacement:Shape	Displacement shape.
Displacement:Fine	Fine detail strength. Layers high-frequency small relief on top.
Displacement:Flares	Root flare. Makes the trunk thicken naturally where it meets the ground. Very effective on single-tree close-ups.
Displacement:Length amount	Displacement amount along the length.
Displacement:Sharpness	Sharpness — how hard or soft the displacement edges are.
Displacement:Mapping	Texture mapping method.
Displacement:U scale / V scale	Texture scale in U/V.
Displacement:Seed	Random seed; change it for a different bump distribution.
Displacement:Feature Exaggeration	Feature exaggeration. Amplifies existing bump features.

UV Mapping

Parameter	Purpose
UV Mapping:Style	UV unwrap method. Different methods determine how bark texture wraps around a branch.
UV Mapping:U / V	Tiling count in U/V. U controls how many times the texture repeats around the circumference, V how many times along the length.
UV Mapping:Tiling	Master control for tiling.
UV Mapping:Create seams	Whether to create UV seams. Seams are needed to unwrap for texture painting.
UV Mapping:Seams seed	Random seed for seam placement.

Checking UVs and texel density

Two render modes exist specifically for checking UVs:

• Texcoord.fx — displays UV coordinates directly (red/green gradient), so flipped or stretched UVs are obvious at a glance.
• Texcoord_Seams.fx — highlights UV seam positions.
• Texel_Density.fx — texel density check. Shows by color whether texture precision is consistent across regions. If the trunk and the twigs differ too much in texel density, the same texture will look blurry on the twigs. This check is mandatory for game assets.

叶片决定了树冠的观感，也占了绝大多数面数。SpeedTree 里做叶片有三个节点可选：

节点	形态	面数	适用
Leaf Mesh	平面卡片或真实网格	中	主流选择，可做出卷曲、翻折等立体感
Batched Leaf	批量打包的叶片	低（渲染开销小）	密集树冠、移动端
Leaf	最简卡片	最低	远景、大规模植被
Frond	一整片羽状复叶	低（效率最高）	棕榈、蕨类、苏铁

Leaves 参数组

参数	作用
Leaves:Type	叶片类型（卡片 / 网格）
Leaves:Size X / Size Y	叶片的宽与长。这两个值要和贴图里叶子的长宽比匹配，否则会拉伸。
Leaves:Scale	整体缩放。
Leaves:Rotation	叶片旋转。配合方差让每片叶子朝向不同。
Leaves:Bend	弯曲。让叶片沿叶脉弯折。
Leaves:Fold	对折角度。让平面卡片沿中轴对折成"V"形，是让卡片叶子有立体感最省事的方法。
Leaves:Twist	扭转。叶片绕自身长轴旋转。
Leaves:Flutter	颤动。叶片在风中的额外抖动。
Leaves:Align	朝向对齐。
Leaves:Spread	散布。叶片离枝条轴线的距离。
Leaves:Distribution	分布曲线。控制叶片沿枝条的疏密。
Leaves:Start angle	起始角。
Leaves:Orientation	朝向控制。

相关参数组

参数组	作用
Local Orientation	局部朝向。让叶片相对父级的朝向偏移。
Deformation	形变。让叶片在风中发生形变。
Sensitivity	敏感度。对光照/风的响应敏感度。
Final Adjustments	最终调整。导出前的最后微调。
Shade Pruning	着色修剪。按受光情况剔除叶片。
Lighting:Translucency	叶片透光。让阳光透过叶子。

Leaves define how the crown reads and account for the vast majority of the polygons. SpeedTree offers three node types for leaves:

Node	Form	Polygons	Use
Leaf Mesh	flat card or real mesh	medium	the mainstream choice; can be curled and folded for a 3D feel
Batched Leaf	batched, packed leaves	low (cheap to render)	dense crowns, mobile
Leaf	the simplest card	lowest	distance, large-scale vegetation
Frond	a whole pinnate compound leaf	low (most efficient)	palms, ferns, cycads

The Leaves parameter group

Parameter	Purpose
Leaves:Type	Leaf type (card / mesh)
Leaves:Size X / Size Y	Leaf width and length. These must match the leaf's aspect ratio in the texture, or it will stretch.
Leaves:Scale	Overall scale.
Leaves:Rotation	Leaf rotation. Pair it with variance so every leaf faces differently.
Leaves:Bend	Bend. Bends the leaf along its midrib.
Leaves:Fold	Fold angle. Folds a flat card along its center axis into a “V” — the cheapest way to give card leaves a 3D feel.
Leaves:Twist	Twist. Rotates the leaf about its own long axis.
Leaves:Flutter	Flutter. Extra leaf shake in the wind.
Leaves:Align	Orientation alignment.
Leaves:Spread	Spread. Distance of leaves from the branch axis.
Leaves:Distribution	Distribution curve. Controls leaf density along the branch.
Leaves:Start angle	Start angle.
Leaves:Orientation	Orientation control.

Related parameter groups

Parameter group	Purpose
Local Orientation	Local orientation. Offsets leaf orientation relative to the parent.
Deformation	Deformation. Lets leaves deform in the wind.
Sensitivity	Sensitivity. Response sensitivity to light and wind.
Final Adjustments	Final adjustments. The last tweaks before export.
Shade Pruning	Shade pruning. Removes leaves based on how lit they are.
Lighting:Translucency	Leaf translucency. Lets sunlight pass through the leaves.

SpeedTree 用顶点色通道承载额外的信息，这是它把“造型数据”和“运行时数据”打包在一起的方式。三个通道各有约定：

通道	参数	存储内容	用途
红 (R)	Vertex Color:Red	环境光遮蔽（AO）	让枝条根部、树冠内部变暗，是“体积感”的主要来源。
绿 (G)	Vertex Color:Green	风力权重	直接决定风动幅度。与 Wind:Weight 配合。
蓝 (B)	Vertex Color:Blue	隐藏 / 剔除信息	控制哪些部分在特定条件下隐藏。
隐藏绿	Vertex Color:Hidden Green	隐藏状态的绿通道值	—

怎么查看

用渲染模式里的 _Vertex Colors 组：

• ___Color.fx —— 显示完整的顶点色 RGB。
• __Red.fx —— 只看红通道，也就是 AO。
• _Green.fx —— 只看绿通道，也就是风力权重。
• Blue.fx —— 只看蓝通道。

为什么 AO 这么重要

程序化生成的树如果没有任何遮蔽信息，树冠内部会和外部一样亮，看起来像“一堆漂浮的纸片”。把 AO 烘进顶点色的红通道后：

• 枝条交接处自然变暗。
• 树冠内部变暗，产生体积感。
• 整棵树的“重量感”就出来了。

SpeedTree 会自动计算这个 AO，一般不需要手工绘制，但要确保渲染时启用了顶点色。

手工绘制顶点色

工具栏里提供了顶点色画笔。相关图标（在 app_data/Property Bar/ 目录）包括：

工具	文件	作用
顶点色笔刷	vertexcolor_brush_icon.png	直接在模型上刷顶点色
顶点编辑	vertex_edit_icon.png	编辑单个顶点
顶点笔刷	vertex_brush_icon.png	批量影响顶点
置换笔刷	displacement_brush_icon.png	手工推移顶点做形变
弯曲笔刷	bend_brush_icon.png	手工弯曲枝条

SpeedTree uses vertex color channels to carry extra information — that is how it packs “shape data” and “runtime data” together. Each of the three channels has a convention:

Channel	Parameter	Stores	Use
Red (R)	Vertex Color:Red	ambient occlusion (AO)	Darkens branch bases and the inside of the crown; the main source of volume.
Green (G)	Vertex Color:Green	wind weight	Directly determines wind amplitude. Works together with Wind:Weight.
Blue (B)	Vertex Color:Blue	hidden / culling information	Controls which parts hide under particular conditions.
Hidden Green	Vertex Color:Hidden Green	green channel value in the hidden state	—

How to view it

Use the _Vertex Colors group of render modes:

• ___Color.fx — shows the full RGB vertex color.
• __Red.fx — red channel only, that is, AO.
• _Green.fx — green channel only, that is, wind weight.
• Blue.fx — blue channel only.

Why AO matters so much

Without any occlusion information, a procedurally generated tree is as bright inside the crown as outside, and it looks like “a pile of floating paper”. Bake AO into the red channel of vertex color and:

• branch junctions darken naturally.
• the inside of the crown darkens, creating volume.
• the whole tree gains a sense of weight.

SpeedTree computes this AO automatically and you generally do not paint it by hand, but make sure vertex color is enabled at render time.

Painting vertex color by hand

The toolbar provides vertex color brushes. The relevant icons (in app_data/Property Bar/) are:

Tool	File	Purpose
vertex color brush	vertexcolor_brush_icon.png	paint vertex color directly on the model
vertex edit	vertex_edit_icon.png	edit individual vertices
vertex brush	vertex_brush_icon.png	affect vertices in bulk
displacement brush	displacement_brush_icon.png	push vertices by hand to deform the mesh
bend brush	bend_brush_icon.png	bend branches by hand

SpeedTree 内置了大量“调试渲染模式”，用来检查模型的各个数据通道。这是排查问题最快的手段——遇到问题先切渲染模式看数据，比盲调参数有效得多。

下面是 v10.2.0 安装目录 render_modes/ 里真实存在的全部模式，按官方分组列出：

光照模式（_Lighting）

模式	用途
____Untextured.fx	无贴图，只看几何体与光照
__Diffuse.fx	只看漫反射贡献
__Specular.fx	只看高光贡献
__Subsurface.fx	只看次表面散射贡献
_Direct.fx	只看直接光
Ambient.fx	只看环境光
Shadow.fx	只看阴影

材质通道模式（_Material）

模式	检查什么
____Color.fx	颜色贴图
____Opacity.fx	不透明度。检查叶片 Alpha 是否干净。
___Normal.fx	法线贴图
___Gloss.fx	光泽度
___Specular.fx	高光
__Metallic.fx	金属度
__Subsurface.fx	次表面颜色
_Subsurface Amount.fx	次表面强度
Custom.fx / Custom2.fx	自定义通道
Height.fx	高度贴图

顶点色模式（_Vertex Colors）

模式	检查什么
___Color.fx	完整顶点色
__Red.fx	红通道 = AO
_Green.fx	绿通道 = 风力权重
Blue.fx	蓝通道 = 隐藏信息

风力权重模式（_Wind Weights）

模式	检查什么
Level 1.fx ～ Level 4.fx	各层级的整体风动权重分布
Ripple.fx	涟漪（叶片高频抖动）权重

其它模式（Other）

模式	用途
____Phong.fx	Phong 光照模型
___Blinn-Phong.fx	Blinn-Phong 光照模型
___Oren-Nayar.fx	Oren-Nayar 漫反射模型，适合粗糙表面
__Lambert.fx	Lambert 漫反射
_Flat.fx	平光，看剪影最好
_Snow.fx	积雪效果预览
Billboard_Subsurface_Amount.fx	公告板的次表面强度
Depth.fx	深度图
Face_Normal_Check.fx	面法线检查，用来找翻转的面
Matcap.fx	Matcap 材质球预览，看形体很好用
Overdraw.fx	重叠绘制检查。颜色越亮说明该区域被重复绘制次数越多，是优化叶片布局的重要依据。
Texcoord.fx	UV 坐标显示
Texcoord_Seams.fx	UV 接缝显示
Texel_Density.fx	纹素密度检查，看贴图精度是否均匀

顶层常用模式

模式	用途
_____Standard.fx	标准渲染（默认）
____Scribed.fx	描边渲染
___AO.fx	只显示 AO
__Albedo_Check.fx	反照率检查
__Saturation_Check.fx	饱和度检查，用于检查颜色是否超出合理范围
__Subsurface_Check.fx	次表面检查
_Lightmap.fx	光照贴图预览

SpeedTree ships a large set of “debug render modes” for inspecting the model's various data channels. This is the fastest way to diagnose problems — when something is wrong, switch render modes and look at the data; it beats tuning parameters blindly.

Below are all the modes that actually exist in the v10.2.0 install directory render_modes/, listed by official group:

Lighting modes (_Lighting)

Mode	Purpose
____Untextured.fx	no texture; geometry and lighting only
__Diffuse.fx	diffuse contribution only
__Specular.fx	specular contribution only
__Subsurface.fx	subsurface scattering contribution only
_Direct.fx	direct light only
Ambient.fx	ambient light only
Shadow.fx	shadows only

Material channel modes (_Material)

Mode	What it checks
____Color.fx	color map
____Opacity.fx	opacity. Checks whether leaf alpha is clean.
___Normal.fx	normal map
___Gloss.fx	glossiness
___Specular.fx	specular
__Metallic.fx	metallic
__Subsurface.fx	subsurface color
_Subsurface Amount.fx	subsurface amount
Custom.fx / Custom2.fx	custom channels
Height.fx	height map

Vertex color modes (_Vertex Colors)

Mode	What it checks
___Color.fx	full vertex color
__Red.fx	red channel = AO
_Green.fx	green channel = wind weight
Blue.fx	blue channel = hidden information

Wind weight modes (_Wind Weights)

Mode	What it checks
Level 1.fx ～ Level 4.fx	shared wind weight distribution per level
Ripple.fx	ripple (high-frequency leaf shake) weight

Other modes

Mode	Purpose
____Phong.fx	Phong lighting model
___Blinn-Phong.fx	Blinn-Phong lighting model
___Oren-Nayar.fx	Oren-Nayar diffuse model, good for rough surfaces
__Lambert.fx	Lambert diffuse
_Flat.fx	flat shading; the best way to read a silhouette
_Snow.fx	snow accumulation preview
Billboard_Subsurface_Amount.fx	billboard subsurface amount
Depth.fx	depth map
Face_Normal_Check.fx	face normal check, for finding flipped faces
Matcap.fx	Matcap preview; great for reading form
Overdraw.fx	overdraw check. Brighter color means that area is drawn over more times — an important basis for optimizing leaf layout.
Texcoord.fx	UV coordinate display
Texcoord_Seams.fx	UV seam display
Texel_Density.fx	texel density check, for consistent texture precision

Common top-level modes

Mode	Purpose
_____Standard.fx	standard render (default)
____Scribed.fx	scribed/outline render
___AO.fx	AO only
__Albedo_Check.fx	albedo check
__Saturation_Check.fx	saturation check, for colors outside a sensible range
__Subsurface_Check.fx	subsurface check
_Lightmap.fx	lightmap preview

植被在游戏里需要碰撞：玩家会撞到树干、子弹会被挡住、物理物体要能挂在树上。SpeedTree 提供多级碰撞方案。

参数组	作用
Collision:Type	碰撞体类型。
Collision:Collision	是否为该节点生成碰撞。
Collision:Radius	碰撞半径。通常比实际几何体略大一点，避免角色“贴脸”。
Leaf Collision:Type	叶片碰撞类型。叶片一般不生成碰撞，但穿行灌木时可能需要。
Leaf Collision:Radius	叶片碰撞半径。
Proxy Collision	在 Tree 根节点上，生成整树的简化碰撞代理。

碰撞体的层级策略

不要给每个枝条都生成碰撞，那样面数会爆炸。合理做法：

层级	碰撞策略
树干（Level 1）	生成圆柱形碰撞，半径取树干实际半径的 1.0～1.1 倍
主枝（Level 2）	只给粗大的主枝生成，或整体忽略
细枝 / 叶片	不生成。用 Tree 根节点上的 Proxy 做整体包裹

专门的碰撞节点有两个：Proxy（碰撞代理）生成贴合树干的低面数碰撞体；Cage（碰撞笼）生成包住整棵树的简化外壳。两者的图标分别是 generator_proxy.tga 和 generator_cage.tga。

Vegetation needs collision in games: players bump into trunks, bullets get blocked, and physics objects have to be able to hang on trees. SpeedTree provides several levels of collision.

Parameter group	Purpose
Collision:Type	Collision body type.
Collision:Collision	Whether to generate collision for this node.
Collision:Radius	Collision radius. Usually slightly larger than the actual geometry so characters do not end up right against the trunk.
Leaf Collision:Type	Leaf collision type. Leaves generally do not generate collision, but it can be needed when walking through shrubs.
Leaf Collision:Radius	Leaf collision radius.
Proxy Collision	On the Tree root node, generates a simplified collision proxy for the whole tree.

Collision strategy by level

Do not generate collision for every branch — the polygon count would explode. A sensible approach:

Level	Collision strategy
Trunk (Level 1)	Generate cylindrical collision with a radius of 1.0–1.1× the trunk's actual radius
Primary branches (Level 2)	Generate only for the thick primary branches, or ignore them entirely
Twigs / leaves	Do not generate. Use the Proxy on the Tree root node to wrap the whole tree

There are two dedicated collision nodes: Proxy (collision proxy) generates a low-poly collision body that hugs the trunk, and Cage (collision cage) generates a simplified shell enclosing the whole tree. Their icons are generator_proxy.tga and generator_cage.tga respectively.

SpeedTree 支持在同一棵树里定义四季表现，通过材质偏移（Material Offset）在季节之间切换。官方示例 samples/Learning/Seasons/Seasons.spm 与 samples/Learning/Material_Offset_Seasons/Material_Offset_Seasons.spm 完整演示了这套流程。

Season 参数

参数	作用
Season:Time scale	季节时间缩放。控制这个节点随季节变化的快慢。
Season:Start offset	起始偏移。让不同节点在不同时间点开始变色。
Season:Descendant offset	子级偏移。让子树比父级晚一点变化，做出“从外向内逐渐变色”的自然过渡。

季节贴图的命名约定

在官方示例 Material_Offset_Seasons/Leaves/ 目录里可以看到真实使用的贴图组：

EasternRedbud_front_1.png            基础（夏季）
EasternRedbud_front_1_spring.png     春季
EasternRedbud_front_1_summer.png     夏季
EasternRedbud_front_1_fall.png       秋季
EasternRedbud_front_1_winter.png     冬季
EasternRedbud_front_1_Opacity.png    不透明度
EasternRedbud_front_1_Normal.png     法线
EasternRedbud_front_1_Subsurface.png 次表面

同一套命名规则也用在 samples/Games/Palm/Clusters/Whole_Frond_Cluster/ 里（Palm_Cluster_2_Summer、_Winter 等）。

材质偏移的三种方式

示例目录里配套了三张示意图，正好对应三种变化方式：

文件	含义
Uniform.png	整棵树统一变色的效果
Variance.png	带随机差异的变色效果（更自然）
Parent_Curve.png	用父级曲线控制变色节奏

推荐用 Variance 方式：真实的秋天不是所有叶子同时变黄，而是有先有后。

SpeedTree lets you define all four seasons inside a single tree and switch between them with material offset. The official samples samples/Learning/Seasons/Seasons.spm and samples/Learning/Material_Offset_Seasons/Material_Offset_Seasons.spm demonstrate the whole workflow.

Season parameters

Parameter	Purpose
Season:Time scale	Season time scale. Controls how quickly this node changes with the season.
Season:Start offset	Start offset. Makes different nodes start changing color at different times.
Season:Descendant offset	Descendant offset. Makes the subtree change slightly later than its parent, producing the natural “color spreading from the outside inward” transition.

The seasonal texture naming convention

In the official sample directory Material_Offset_Seasons/Leaves/ you can see the texture set actually used:

EasternRedbud_front_1.png             base (summer)
EasternRedbud_front_1_spring.png      spring
EasternRedbud_front_1_summer.png      summer
EasternRedbud_front_1_fall.png        fall
EasternRedbud_front_1_winter.png      winter
EasternRedbud_front_1_Opacity.png     opacity
EasternRedbud_front_1_Normal.png      normal
EasternRedbud_front_1_Subsurface.png  subsurface

The same naming convention is used in samples/Games/Palm/Clusters/Whole_Frond_Cluster/ (Palm_Cluster_2_Summer, _Winter and so on).

Three ways to do material offset

The sample directory ships three diagram images, one for each way the change can vary:

File	Meaning
Uniform.png	The whole tree changes color uniformly
Variance.png	Color change with random variation (more natural)
Parent_Curve.png	Color change rhythm driven by a parent curve

The Variance approach is recommended: real autumn does not turn every leaf yellow at the same moment — some go first and some follow later.

Growth 让植物“长出来”。它不是简单地缩放，而是按枝条生长顺序逐级展开，做出真正像植物生长的动画。

参数	作用
Growth:Timing	生长时序。控制这个节点在整段动画的什么时间点开始生长。
Growth:Speed scale	生长速度。不同节点可以有不同的速度。
Growth:Radius	生长半径。枝条在生长过程中由细变粗。
Growth:Unfurl	展开动画。叶片从卷曲状态展开的过程。
Growth:Noise	生长噪波。让生长过程不是匀速的，更自然。
Growth:Smoothing	平滑。让生长过渡更柔和。
Growth:Mapping	生长映射。控制生长动画的数据如何分布。
Growth:Allow extension control	允许扩展控制。

官方生长示例

文件	演示内容
samples/Learning/Growth/Sapling_Growth.spm	幼苗生长
samples/Learning/Growth/Trellis_Growth.spm	沿棚架生长（配套 trellis.fbx 与 trellis_ao.png）

导出生长动画

export_presets/VFX/Growth.ini 是专门的生长动画导出预设。生长动画通常导出为 Alembic（.abc）格式，在 Houdini、Maya、Blender 里做后续渲染。注意：生长动画是逐帧烘焙的，文件会比较大，只对近景镜头使用。

Growth makes a plant “grow out”. It is not a simple scale-up: it unfolds level by level in branch growth order, producing an animation that really reads as a plant growing.

Parameter	Purpose
Growth:Timing	Growth timing. Controls at what point in the overall animation this node starts growing.
Growth:Speed scale	Growth speed. Different nodes can grow at different speeds.
Growth:Radius	Growth radius. Branches thicken from thin to thick as they grow.
Growth:Unfurl	Unfurl animation. The process of a leaf opening out from a curled state.
Growth:Noise	Growth noise. Makes growth non-uniform, which looks more natural.
Growth:Smoothing	Smoothing. Softens the growth transition.
Growth:Mapping	Growth mapping. Controls how the growth animation data is distributed.
Growth:Allow extension control	Allow extension control.

Official growth samples

File	What it demonstrates
samples/Learning/Growth/Sapling_Growth.spm	sapling growth
samples/Learning/Growth/Trellis_Growth.spm	growth along a trellis (with trellis.fbx and trellis_ao.png)

Exporting growth animation

export_presets/VFX/Growth.ini is the export preset dedicated to growth animation. Growth animation is usually exported as Alembic (.abc) for downstream rendering in Houdini, Maya or Blender. Note that growth animation is baked frame by frame, so the files are fairly large — use it only for close-up shots.

Skin（蒙皮）解决的是枝条交接处的几何问题。两根枝条相接时，如果只是简单地把两个圆柱插在一起，接缝处会出现穿插、破面或明显的硬边。Skin 负责让交接处平滑过渡。

参数	作用
Skin:Type	蒙皮类型。不同算法适用于不同粗细的枝条。
Skin:Radius	蒙皮影响半径。半径越大，过渡区域越宽。
Skin:Smooth	平滑程度。
Skin:Welding	焊接。把交接处的顶点合并，消除裂缝。
Skin:Splits	分叉处理。控制分叉处的几何生成方式。
Skin:Squash	压扁。让交接处稍微压扁，更符合真实树干的形态。
Skin:Subdivision	细分。在交接处增加几何密度。
Skin:Roll	滚转。
Skin:Visibility	可见性控制。
Skin:Intersection	相交处理。控制几何体互相穿插时的表现。
Skin:Light seam reduction	接缝光照弱化。消除接缝处的光照不连续，避免出现一条亮线或暗线。

Skin solves the geometry problem at branch junctions. When two branches meet, simply pushing two cylinders into each other produces intersections, broken faces or an obvious hard edge at the seam. Skin is responsible for making the junction transition smoothly.

Parameter	Purpose
Skin:Type	Skin type. Different algorithms suit branches of different thickness.
Skin:Radius	Skin influence radius. The larger the radius, the wider the transition region.
Skin:Smooth	Degree of smoothing.
Skin:Welding	Welding. Merges vertices at the junction to eliminate cracks.
Skin:Splits	Split handling. Controls how geometry is generated at a fork.
Skin:Squash	Squash. Flattens the junction slightly, which better matches real trunk form.
Skin:Subdivision	Subdivision. Adds geometry density at the junction.
Skin:Roll	Roll.
Skin:Visibility	Visibility control.
Skin:Intersection	Intersection handling. Controls the result when geometry passes through itself.
Skin:Light seam reduction	Light seam reduction. Removes lighting discontinuity at the seam so you do not get a bright or dark line.

这是两组用途完全不同的机制，官方文档有一句关键提示：

2.15.1　两套机制的分工

	Resolution 分辨率	Level of Detail（动态 LOD）
面向	VFX / 影视	实时 / 游戏
形态	同一模型的几个固定质量档位	随距离平滑连续地简化
档位	High / Medium / Low / Draft	连续过渡，无离散级别跳变
控制方式	Resolution 曲线（每个参数一条）	LOD 曲线（在 LOD 属性组里）
导出	VFX 导出按选定分辨率输出	Games 导出烘焙出多个 LOD

2.15.2　Resolution 分辨率（VFX）

Resolution 让同一个模型拥有四个质量状态。大多数与面数相关的属性都带有一条 Resolution 曲线——例如某属性在 High 下是 60 段，在 Medium 下曲线取值 0.75，就变成 45 段。

还有两个更彻底的用法：

• Generation:Shared:Active —— 按分辨率整批启用/关闭生成器。曲线值 >0.5 启用，<0.5 关闭。
• Generation:Knockout:+Resolution —— 按分辨率增减节点剔除量。

工作习惯建议：建模时保持 High，模型保存为 Medium，做重度编辑时切到 Draft。

2.15.3　动态 LOD（游戏）

SpeedTree 的 LOD 是动态的——它随距离平滑变化，而不是在几个离散级别之间硬切。这正是它相比传统 LOD 的最大优势：不会看到明显的跳变。

开启方式（二选一）：

• Tree Window 工具栏 → LOD → 勾选 Dynamic LOD；
• Tree 生成器属性 → Dynamic LOD 组 → 勾选 Enable。

开启后 LOD 指示器可编辑。默认是 Manual 模式，拖动箭头即可手动改变 LOD 并观察面数变化；切换到 Screen Area 模式后，相机动得越远树自动变得越简单。

过渡时发生了什么

这是理解 SpeedTree LOD 的关键。在过渡过程中，树的某些部分会被智能移除以降低复杂度，同时保持过渡无缝。做法是分析树体、找出被遮挡在内部的部分。一个将被移除的部分会先缩小到不可见，然后才在下一个阶段被彻底删除。

几何类型	过渡行为
枝条	先收缩到自己的脊线，然后消失。
叶片	一部分叶片收缩消失，同时保留下来的叶片会长大，以维持树冠轮廓。

这带来一个很重要的推论：被 LOD 隐藏的枝条只是“隐形”，它上面的叶片仍然保留。所以减少枝条数量不等于减少叶片数量。反过来说，如果想让低 LOD 真正省面，必须同时处理叶片。

控制 LOD 的两个层面

全局层面——Tree 生成器的 Dynamic LOD 组里有一组 LOD 曲线，用来控制整段 LOD 过渡中各类几何体的削减幅度（枝条、叶片、装饰物等各有一条）。

单个生成器层面——每个生成器都有自己的 LOD 相关参数：

参数	作用
Dynamic LOD:Weight	重要。影响谁会被移除。枝条的移除基于它的尺寸和它在树中被“藏”得有多好；而 Weight 会影响这个计算——权重高的枝条会“赢过”权重低的枝条，从而留在树里。
Grow Scale	控制保留下来的叶片长大多少。
Jumble	给内部叶片的移除过程加入噪波。
Optimization	让 Modeler 智能决定在哪里减段而保持形状。
Mesh Index	网格 LOD：随该 LOD 曲线下降，逐渐换用更低质量的网格版本。

网格 LOD 与 Mesh Anchors 的陷阱

在可以用网格的部分（叶片、羽叶等），可以在 LOD 变化时切换到低质量版本的网格。网格 LOD 级别在 Mesh Asset Bar 里设置，随 Mesh Index 属性上的 LOD 曲线下降，逐渐选用更低级别的网格。

公告板（Billboard）

启用公告板会在 LOD 序列末尾追加一级：用从多个视角拍摄的树照片拼成一张公告板图集，渲染时只显示朝向相机的那几个视角。这是植被性能的关键——一棵远处的树可能只占几十个三角面。

相关控制：Billboard start（从哪一级开始用公告板）、Billboard end、Screen area scale。导出时还有 Faces（面数）、Top down（俯视）、Top down height % 等选项。

参考实测的默认值：Unity 预设的 BillboardCount=8、BillboardTopDown=true、BillboardTopDownHeight=0.5；SpeedTree Runtime SDK 预设则是 BillboardCount=12。

These are two mechanisms with completely different purposes, and the official documentation has one key note about them:

2.15.1　How the two mechanisms divide the work

	Resolution	Level of Detail (dynamic LOD)
Aimed at	VFX / film	Real time / games
Form	A few fixed quality tiers of the same model	Simplification that is smooth and continuous with distance
Tiers	High / Medium / Low / Draft	Continuous transition, with no discrete level popping
Control	Resolution curves (one per parameter)	LOD curves (inside the LOD property group)
Export	VFX export outputs the selected resolution	Games export bakes out several LODs

2.15.2　Resolution (VFX)

Resolution gives a single model four quality states. Most polygon-related properties carry a Resolution curve — for example, if a property is 60 segments at High and the curve reads 0.75 at Medium, it becomes 45 segments.

There are two more thorough uses:

• Generation:Shared:Active — enables or disables generators in bulk by resolution. A curve value >0.5 enables them, <0.5 disables them.
• Generation:Knockout:+Resolution — increases or decreases the node knockout amount by resolution.

A suggested working habit: model at High, save the model as Medium, and switch to Draft for heavy editing.

2.15.3　Dynamic LOD (games)

SpeedTree's LOD is dynamic — it changes smoothly with distance rather than hard-switching between a few discrete levels. This is precisely its greatest advantage over conventional LOD: you do not see obvious popping.

Two ways to enable it (either one will do):

• Tree Window toolbar → LOD → tick Dynamic LOD;
• Tree generator properties → Dynamic LOD group → tick Enable.

Once enabled the LOD indicator becomes editable. The default is Manual mode, where dragging the arrow changes the LOD by hand so you can watch the polygon count change; switch to Screen Area mode and the further the camera moves away, the simpler the tree becomes automatically.

What happens during a transition

This is the key to understanding SpeedTree LOD. During a transition, parts of the tree are intelligently removed to reduce complexity while keeping the transition seamless. It does this by analyzing the tree and finding the parts that are hidden inside. A part that is about to be removed first shrinks until it is invisible, and only then is it deleted entirely in the next stage.

Geometry type	Transition behavior
Branches	First shrink into their own spine, then disappear.
Leaves	Some leaves shrink away, while the leaves that remain grow larger, to preserve the crown silhouette.

This leads to a very important corollary: a branch hidden by LOD is only “invisible”; the leaves on it are still kept. So reducing the branch count is not the same as reducing the leaf count. Conversely, if you want a low LOD to genuinely save polygons, you must handle the leaves as well.

Two levels of LOD control

Global level — the Tree generator's Dynamic LOD group contains a set of LOD curves that control how much each kind of geometry is reduced across the whole LOD transition (one curve each for branches, leaves, decorations and so on).

Individual generator level — every generator has its own LOD-related parameters:

Parameter	Purpose
Dynamic LOD:Weight	Important. Affects what gets removed. Branch removal is based on its size and on how well it is “hidden” in the tree; Weight influences that calculation — a branch with a higher weight wins over one with a lower weight and stays in the tree.
Grow Scale	Controls how much the surviving leaves grow.
Jumble	Adds noise to the removal of interior leaves.
Optimization	Lets the Modeler decide intelligently where to drop segments while preserving shape.
Mesh Index	Mesh LOD: as that LOD curve descends, progressively switches to lower-quality mesh versions.

The mesh LOD and Mesh Anchors trap

Where meshes can be used (leaves, fronds and so on), you can switch to a lower-quality mesh version as the LOD changes. Mesh LOD levels are set in the Mesh Asset Bar, and as the LOD curve on the Mesh Index property descends, progressively lower mesh levels are selected.

Billboard

Enabling billboards appends one level at the end of the LOD sequence: photographs of the tree taken from several viewpoints are assembled into a billboard atlas, and at render time only the views facing the camera are shown. This is the key to vegetation performance — a distant tree may occupy only a few dozen triangles.

Related controls: Billboard start (from which level billboards begin), Billboard end, Screen area scale. At export there are also Faces, Top down, Top down height % and other options.

For reference, the measured defaults: the Unity preset has BillboardCount=8, BillboardTopDown=true, BillboardTopDownHeight=0.5; the SpeedTree Runtime SDK preset has BillboardCount=12.

文件格式

扩展名	说明
.spm	SpeedTree Modeler 的模型文件。本质是 gzip 压缩的 XML，记录了完整的节点树与所有参数值。
.stt	SpeedTree Template，模板文件。同样压缩的 XML，保存的是“一组节点”而非完整模型。
.stmat	材质文件。
.xml	SpeedTree XML 格式，未压缩的交换格式，便于程序化处理与版本对比。

内置模板（tree_templates/）

安装目录下的模板是上手最快的方式。v10.2.0 的真实模板列表：

Games 模板（面向游戏，面数与 LOD 已优化）：

模板	用途
Blank.spm	空文件，只有一个 Tree 根节点。完全从零开始用这个。
Broadleaf.spm	阔叶树。最通用的起点。
Conifer.spm	针叶树（松、杉）。
Palm.spm	棕榈。
Cluster.spm	叶簇，用于拼装复杂树冠。
Grass.spm	草。
Plant.spm	小型植物。
Stump.spm	树桩。
Vine.spm	藤蔓。

VFX 模板（面向影视，几何更细、含手绘与造型控制）：

模板	用途
__Broadleaf.spm	阔叶树（VFX 版）
_Conifer.spm / Pine.spm	针叶树 / 松树
Palm.spm	棕榈
__Bush.spm	灌木
_Grass.spm / Grass Weeds.spm	草 / 杂草
_Flower.spm	花
_Plant.spm	小型植物
_Stump.spm	树桩
_Vine.spm	藤蔓
Sapling.spm	幼苗
Base_Split.spm	分裂式根部
Base_Umbrella.spm	伞状根部
Base_Weathered.spm	风化根部
Hand_Drawn_Subd.spm	手绘 + 细分
Shape_Controlled.spm	形状控制

内置组合模板（templates/combined/）

这些是节点级的“零件模板”，可以直接拖进节点树。文件名前的下划线表示它在菜单里的缩进层级：

模板	内容
Base.stt	基础根盘
Reference.stt	参考对象
Knot.stt / Decal.stt / Cavity.stt / Gash.stt / Lump.stt / Peeling_Bark.stt	各种表面装饰：节疤、贴花、凹陷、伤口、隆起、剥落树皮
Roots.stt	根系
Shell.stt	外壳
Target.stt	目标点
Mesh detail.stt	网格细节
__Single.stt / __Bifurcating.stt / __Little.stt / __Big.stt / __Twigs.stt / _Tubes.stt	各种枝条形态
___Alternating.stt / ___Opposite.stt / ___Whorled.stt / __Scattered.stt	叶片排列方式：互生 / 对生 / 轮生 / 散生
___Trunk.stt / _____Trunks_Tube.stt / _____Trunks__Old.stt / _____Trunks__Split.stt / _____Trunks__Tall.stt / _____Trunks_Several.stt / _____Trunks_Hand-drawn.stt	各种树干形态：管状、苍老、分裂、高瘦、多干、手绘
_______Cap_.stt / _______Fin.stt / _______Knot.stt / _______Vine.stt / _______Zone.stt	封顶 / 鳍片 / 节疤 / 藤蔓 / 区域
________Frond.stt / _________Batched_leaf.stt / __________Branch.stt / __________Leaf.stt	羽叶 / 批量叶片 / 枝 / 叶

官方学习示例（samples/Learning/）

这是最有价值的学习材料，每个目录都针对一个专门主题：

目录	学习内容
Forces/	力场系统：衰减、弹性、几何体力场、网格爬行
Growth/	生长动画：幼苗生长、沿棚架生长
Seasons/	四季变化
Material_Offset_Seasons/	材质偏移做季节变化（含 Uniform / Variance / Parent_Curve 三种示意图）
Photogrammetry/	摄影测量：把扫描件接入程序化树、缝合、网格细节
Custom_Spines/	自定义脊线（含 LOD1/LOD2 网格）
Vines/	藤蔓：手绘藤蔓与藤蔓模拟
Projector/	投影器
References/	参考图使用
Rules/	规则脚本：Conifer_Simple_Rules.spm 与 Oak_Complex_Rules.spm
Subdivision_Surface/	细分曲面

成品示例

文件	说明
samples/VFX/Sample_Broadleaf/Broadleaf_Field.spm	阔叶树丛（单株）
samples/VFX/Sample_Broadleaf/Broadleaf_Forest.spm	阔叶树林（多株）
samples/VFX/Sample_Pine/Pine.spm	松树（含树皮置换贴图示例）
samples/VFX/Sample_Palm/Palm.spm	棕榈
samples/VFX/Sample_Mushroom/Mushroom.spm	蘑菇（展示非树木类的做法）
samples/Games/Palm/Palm_Desktop.spm	游戏版棕榈（桌面精度）
samples/Games/Conifer/	针叶树素材库（球果、针叶簇、树皮贴图）

File formats

Extension	Notes
.spm	The SpeedTree Modeler model file. Essentially gzip-compressed XML, recording the complete node tree and all parameter values.
.stt	SpeedTree Template. Also compressed XML, but it stores “a set of nodes” rather than a complete model.
.stmat	Material file.
.xml	SpeedTree XML format, an uncompressed interchange format that is convenient for procedural processing and version comparison.

Built-in templates (tree_templates/)

The templates in the install directory are the fastest way to get started. The real template list in v10.2.0:

Games templates (game-oriented, with polygon counts and LOD already optimized):

Template	Use
Blank.spm	An empty file containing only a Tree root node. Use this to start completely from scratch.
Broadleaf.spm	Broadleaf tree. The most general starting point.
Conifer.spm	Conifer (pine, fir).
Palm.spm	Palm.
Cluster.spm	Leaf cluster, for assembling complex crowns.
Grass.spm	Grass.
Plant.spm	Small plants.
Stump.spm	Tree stump.
Vine.spm	Vine.

VFX templates (film-oriented, finer geometry, with hand-drawn and shape controls):

Template	Use
__Broadleaf.spm	broadleaf tree (VFX version)
_Conifer.spm / Pine.spm	conifer / pine
Palm.spm	palm
__Bush.spm	shrub
_Grass.spm / Grass Weeds.spm	grass / weeds
_Flower.spm	flower
_Plant.spm	small plant
_Stump.spm	stump
_Vine.spm	vine
Sapling.spm	sapling
Base_Split.spm	split root base
Base_Umbrella.spm	umbrella root base
Base_Weathered.spm	weathered root base
Hand_Drawn_Subd.spm	hand drawn + subdivision
Shape_Controlled.spm	shape controlled

Built-in combined templates (templates/combined/)

These are node-level “part templates” that can be dragged straight into the node tree. The leading underscores in the file names indicate their indentation level in the menu:

Template	Content
Base.stt	basic root flare
Reference.stt	reference object
Knot.stt / Decal.stt / Cavity.stt / Gash.stt / Lump.stt / Peeling_Bark.stt	Surface decorations of various kinds: knot, decal, cavity, gash, lump, peeling bark
Roots.stt	roots
Shell.stt	shell
Target.stt	target point
Mesh detail.stt	mesh detail
__Single.stt / __Bifurcating.stt / __Little.stt / __Big.stt / __Twigs.stt / _Tubes.stt	branch forms of various kinds
___Alternating.stt / ___Opposite.stt / ___Whorled.stt / __Scattered.stt	leaf arrangements: alternate / opposite / whorled / scattered
___Trunk.stt / _____Trunks_Tube.stt / _____Trunks__Old.stt / _____Trunks__Split.stt / _____Trunks__Tall.stt / _____Trunks_Several.stt / _____Trunks_Hand-drawn.stt	trunk forms of various kinds: tubular, old, split, tall, multi-trunk, hand-drawn
_______Cap_.stt / _______Fin.stt / _______Knot.stt / _______Vine.stt / _______Zone.stt	cap / fin / knot / vine / zone
________Frond.stt / _________Batched_leaf.stt / __________Branch.stt / __________Leaf.stt	frond / batched leaf / branch / leaf

Official learning samples (samples/Learning/)

This is the most valuable learning material of all; each directory targets one specific topic:

Directory	What to learn
Forces/	The force system: attenuation, bounce, geometry force, mesh crawling
Growth/	Growth animation: sapling growth, growth along a trellis
Seasons/	Seasonal change
Material_Offset_Seasons/	Material offset for seasonal change (with the three diagrams Uniform / Variance / Parent_Curve)
Photogrammetry/	Photogrammetry: bringing scans into a procedural tree, stitching, mesh detail
Custom_Spines/	Custom spines (with LOD1/LOD2 meshes)
Vines/	Vines: hand-drawn vines and vine simulation
Projector/	Projector
References/	Using reference images
Rules/	Rule scripts: Conifer_Simple_Rules.spm and Oak_Complex_Rules.spm
Subdivision_Surface/	Subdivision surface

Finished samples

File	Notes
samples/VFX/Sample_Broadleaf/Broadleaf_Field.spm	Broadleaf grove (single tree)
samples/VFX/Sample_Broadleaf/Broadleaf_Forest.spm	Broadleaf forest (multiple trees)
samples/VFX/Sample_Pine/Pine.spm	Pine (with a bark displacement map example)
samples/VFX/Sample_Palm/Palm.spm	Palm
samples/VFX/Sample_Mushroom/Mushroom.spm	Mushroom (showing a non-tree approach)
samples/Games/Palm/Palm_Desktop.spm	Game palm (desktop precision)
samples/Games/Conifer/	Conifer asset library (cones, needle clusters, bark textures)

一个完整的植被制作流程大致是八个阶段。无论做树、灌木还是草，这个骨架都适用。

阶段一：定目标

动手前先想清楚三件事，它们决定了后面所有参数的方向：

问题	影响
用途：游戏还是影视？	游戏需要 LOD、碰撞、严格的面数预算；影视可以上百万面，用 Alembic 输出。
观察距离：近景特写还是远景填充？	近景要置换、要叶片网格；远景用卡片叶片和公告板就够。
面数预算：单株多少面？	移动端单株 2k–10k；PC 游戏 15k–60k；影视不限。这个数字要在建模时就守着。

阶段二：选起点

起点	适用
tree_templates/Games/Blank.spm	完全从零，最理解原理，但最慢。
对应物种模板（Broadleaf / Conifer / Palm…）	推荐。已有合理的节点结构，改参数即可，效率最高。
打开官方成品示例另存	学习时用。能看到成熟项目的参数配置。

阶段三：定比例

SpeedTree 里 1 单位 = 1 米（可通过 Units 设置调整）。一定要先确定树的真实高度，否则后面所有参数都是凭感觉调，导出到引擎里会大小失调。

植物	真实高度参考
草	0.1 – 0.6 m
灌木	0.8 – 3 m
小乔木 / 幼苗	3 – 6 m
阔叶乔木	10 – 25 m
针叶乔木	15 – 40 m
棕榈	5 – 20 m

SpeedTree 在视图里有一个人形高度指示器，用来快速校对比例。官方文档给出的等价值是：

单位	人形指示器的数值
米 (m)	1.8
厘米 (cm)	182
英尺 (feet)	6
英寸 (inches)	72
码 (yards)	2

把指示器设成上面对应的值，它就代表一个 1.8 米高的人。用它来对照树高，比凭感觉估要可靠得多。

阶段四：搭骨架

先只做枝干，关掉叶片。这一步的目标是让“光秃秃的树”看起来就合理：

1. 调树干 Branch 的 Spine:Length、Spine:Shape，让它有自然的锥度和弯曲。
2. 调 Generation:Mode 与数量，让主枝分布合理。
3. 加 Forces:Gnarl 打破规整。
4. 逐级往下加子 Branch，每一级都确认形态合理后再加下一级。

阶段五：加叶片

1. 在末梢枝下加 Leaf Mesh / Frond。
2. 先只放一片叶子，把尺寸、朝向、对折角度调好。
3. 再调数量与分布曲线，让它成为一簇。
4. 用 Overdraw 渲染模式检查有没有严重堆叠。

阶段六：表面细节

• 材质：指定 Color / Normal / Opacity / Subsurface 等贴图。
• UV：调 UV Mapping:U / V 让树皮纹理比例正确，用 Texel_Density.fx 检查。
• 置换：加 Displacement:Amount，近景才开。
• 装饰：加 Knot（节疤）、Decal（苔藓）增加故事性。

阶段七：风与 LOD

1. 按层级递增设置 Wind:Weight，用 _Wind Weights 模式检查。
2. 在 Tree 根节点设置 Level of Detail:Count，逐级降面。
3. 设置 Billboard start，让远处用公告板。
4. 加碰撞（Collision:Radius 或 Proxy）。

阶段八：导出与验证

1. 选对应引擎的导出预设。
2. 导出后在引擎里实际观察：LOD 切换是否跳变、风动是否自然、贴图有没有丢。
3. 用引擎的性能分析工具确认 draw call 与面数符合预期。

A complete vegetation production workflow has roughly eight stages. Whether you are making a tree, a shrub or grass, the same skeleton applies.

Stage 1: Set the goal

Before you start, be clear about three things; they determine the direction of every parameter that follows:

Question	Impact
Use: game or film?	Games need LOD, collision and a strict polygon budget; film can go to millions of polygons and output Alembic.
Viewing distance: close-up hero shot, or distant filler?	Close-ups need displacement and leaf meshes; distance is fine with card leaves and billboards.
Polygon budget: how many polygons per tree?	Mobile 2k–10k per tree; PC games 15k–60k; film unlimited. Keep to that number from the moment you start modeling.

Stage 2: Choose a starting point

Starting point	When to use it
tree_templates/Games/Blank.spm	Completely from scratch. You learn the principles best, but it is the slowest route.
The template for your species (Broadleaf / Conifer / Palm…)	Recommended. It already has a sensible node structure, so you just change parameters — by far the most efficient.
Open an official finished sample and save it under a new name	For learning. You can see how a mature project is configured.

Stage 3: Fix the scale

In SpeedTree 1 unit = 1 meter (adjustable in the Units settings). Decide the tree's real height first, or every parameter afterward is guesswork and the export will be the wrong size in the engine.

Plant	Real height reference
Grass	0.1 – 0.6 m
Shrub	0.8 – 3 m
Small tree / sapling	3 – 6 m
Broadleaf tree	10 – 25 m
Conifer	15 – 40 m
Palm	5 – 20 m

SpeedTree has a human-height indicator in the viewport for checking scale quickly. The equivalent values given in the official documentation are:

Unit	Value for the human figure indicator
Meters (m)	1.8
Centimeters (cm)	182
Feet	6
Inches	72
Yards	2

Set the indicator to the matching value above and it represents a person 1.8 m tall. Comparing tree height against it is far more reliable than eyeballing.

Stage 4: Build the skeleton

Work on branches only at first, with leaves turned off. The goal of this stage is to make the bare tree look plausible on its own:

1. Adjust the trunk Branch's Spine:Length and Spine:Shape so it has natural taper and curvature.
2. Adjust Generation:Mode and the count so the primary branches are distributed sensibly.
3. Add Forces:Gnarl to break the regularity.
4. Add child Branches level by level, confirming each level looks right before adding the next.

Stage 5: Add leaves

1. Add a Leaf Mesh / Frond under the tip twigs.
2. Place just one leaf first and get its size, orientation and fold angle right.
3. Then adjust the count and the distribution curve to turn it into a cluster.
4. Use the Overdraw render mode to check for serious stacking.

Stage 6: Surface detail

• Material: assign the Color / Normal / Opacity / Subsurface maps and so on.
• UV: adjust UV Mapping:U / V so the bark texture scale is correct, and check it with Texel_Density.fx.
• Displacement: add Displacement:Amount, enabled only for close-ups.
• Decoration: add Knots (knots) and Decals (moss) to give the tree a story.

Stage 7: Wind and LOD

1. Set Wind:Weight increasing with level, and check it with the _Wind Weights modes.
2. Set Level of Detail:Count on the Tree root node and reduce polygons level by level.
3. Set Billboard start so distance uses billboards.
4. Add collision (Collision:Radius or a Proxy).

Stage 8: Export and verify

1. Choose the export preset for your engine.
2. After export, look at it in the engine: does the LOD switch pop, does the wind look natural, are any textures missing.
3. Use the engine's profiling tools to confirm the draw calls and polygon counts match expectations.

SpeedTree 内置了针对不同目标的导出预设，位于安装目录 export_presets/。v10.2.0 的真实预设列表：

游戏引擎预设（Games/）

预设	目标	说明
__UnrealEngine (ST).ini	Unreal Engine	输出 UE 原生的 SpeedTree 格式，配合 UE 的 SpeedTree 导入器使用，风力与 LOD 由引擎运行时驱动。
__UnrealEngine (ST9).ini	Unreal Engine（ST9 兼容）	针对旧版 UE 的 SpeedTree 9 格式兼容。
___Unity.ini	Unity	输出 Unity 的 SpeedTree 资源。
__Unity (one draw call).ini	Unity（单次绘制）	合并为一次 draw call，适合大量重复植被，性能最优但灵活性降低。
_SpeedTree Runtime SDK.ini	SpeedTree 运行时 SDK	给自研引擎使用，需要自行集成 SDK。
Generic FBX.ini	通用 FBX	不带引擎特定数据的通用格式，用于导入其它 DCC 工具。

影视与 DCC 预设（VFX/）

预设	目标
____Maya.ini	Autodesk Maya
___3D Studio MAX.ini	3ds Max
___Houdini.ini	Houdini
__Blender.ini	Blender
__Cinema4D.ini	Cinema 4D
__FBX.ini	通用 FBX
_Alembic.ini	Alembic（.abc）。影视标准，支持生长动画与风动的逐帧烘焙。
_USD.ini	Universal Scene Description。现代影视管线标准。
Growth.ini	生长动画专用导出
Wind.ini	风力动画专用导出

安装目录 scripts/ 下还提供了各 DCC 的导入脚本：

scripts/3ds Max/
scripts/Blender/
scripts/Cinema4D/
scripts/Houdini/
scripts/Maya/

用这些脚本导入可以保留风力与 LOD 信息，比直接导入 FBX 效果好。

导出前检查清单

检查项	怎么查
面数是否在预算内	看视图区统计的 TOTAL 数字
叶片有没有严重堆叠	Overdraw.fx 渲染模式
贴图精度是否均匀	Texel_Density.fx 渲染模式
有没有翻转的面	Face_Normal_Check.fx 渲染模式
叶片 Alpha 是否干净	_Material/____Opacity.fx 渲染模式
风力权重是否合理	_Wind Weights/Level 1~4.fx
LOD 切换是否跳变	用 LOD 按钮逐级切换观察
材质贴图路径是否正确	确认没有丢贴图警告

面数预算参考

资产类型	LOD0 面数	LOD 级数
英雄树（近景主角）	8,000 – 15,000	4 级，最后一级约 200 面 + 公告板
背景树	3,000 – 6,000	3 级
灌木	500 – 2,000	2 级 + 公告板
草（每丛）	30 – 80	单级（见草案例的硬性约束）

同一批第三方资料还给出了剔除距离的量级参考：大树约 8,000–15,000 单位、灌木 3,000–5,000、草 1,500–3,000；并且建议剔除的起始距离取结束距离的约 80%，配合引擎的 Dithered LOD Transition 来消除跳变。

作为对照，本机官方示例 Broadleaf_Field.spm 的总面数是 3,032,522，属于影视级密度，不能直接用于游戏。

SpeedTree ships export presets for different targets, in the install directory export_presets/. The real preset list in v10.2.0:

Game engine presets (Games/)

Preset	Target	Notes
__UnrealEngine (ST).ini	Unreal Engine	Outputs UE's native SpeedTree format, used together with UE's SpeedTree importer; wind and LOD are driven by the engine runtime.
__UnrealEngine (ST9).ini	Unreal Engine (ST9 compatible)	SpeedTree 9 format compatibility for older UE versions.
___Unity.ini	Unity	Outputs a Unity SpeedTree asset.
__Unity (one draw call).ini	Unity (single draw)	Merges into a single draw call, ideal for large amounts of repeated vegetation; the best performance but less flexibility.
_SpeedTree Runtime SDK.ini	SpeedTree Runtime SDK	For in-house engines; you integrate the SDK yourself.
Generic FBX.ini	Generic FBX	A generic format without engine-specific data, for importing into other DCC tools.

Film and DCC presets (VFX/)

Preset	Target
____Maya.ini	Autodesk Maya
___3D Studio MAX.ini	3ds Max
___Houdini.ini	Houdini
__Blender.ini	Blender
__Cinema4D.ini	Cinema 4D
__FBX.ini	Generic FBX
_Alembic.ini	Alembic (.abc). The film standard, supporting frame-by-frame baking of growth animation and wind.
_USD.ini	Universal Scene Description. The modern film pipeline standard.
Growth.ini	Dedicated growth animation export
Wind.ini	Dedicated wind animation export

The install directory scripts/ also provides import scripts for the various DCCs:

scripts/3ds Max/
scripts/Blender/
scripts/Cinema4D/
scripts/Houdini/
scripts/Maya/

Importing with these scripts preserves the wind and LOD information, which works better than importing the FBX directly.

Pre-export checklist

Check	How to check it
Are the polygons within budget	read the TOTAL number in the viewport statistics
Is there serious leaf stacking	the Overdraw.fx render mode
Is texture precision consistent	the Texel_Density.fx render mode
Are there any flipped faces	the Face_Normal_Check.fx render mode
Is the leaf alpha clean	the _Material/____Opacity.fx render mode
Are the wind weights sensible	_Wind Weights/Level 1~4.fx
Does the LOD switch pop	step through the levels with the LOD button
Are the material texture paths correct	confirm there are no missing-texture warnings

Polygon budget reference

Asset type	LOD0 polygons	LOD levels
Hero tree (close-up protagonist)	8,000 – 15,000	4 levels, last level about 200 polygons + billboard
Background tree	3,000 – 6,000	3 levels
Shrub	500 – 2,000	2 levels + billboard
Grass (per clump)	30 – 80	single level (see the hard constraint in the grass case)

The same third-party sources also give order-of-magnitude culling distances: roughly 8,000–15,000 units for large trees, 3,000–5,000 for shrubs and 1,500–3,000 for grass; and they suggest setting the culling start distance at about 80% of the end distance, together with the engine's Dithered LOD Transition, to remove popping.

For comparison, the official sample Broadleaf_Field.spm on this machine has a total of 3,032,522 polygons — film-grade density, not directly usable in a game.

手绘工作流

程序化生成适合做“整体合理”的树，但主角树的关键枝条往往需要更强的造型控制。这时用手绘模式：

1. 打开工具栏的 Freehand。
2. 添加一个 Spine 节点，在视图里拖出枝条走向。
3. 用 Hand Drawn:Resample 重采样，让手绘曲线平滑。
4. 把 Branch 或 Leaf Mesh 挂到 Spine 下，沿手绘路径生长。
5. 用 Convert generator to hand drawn 也可以把已有的程序化枝条转成手绘，再做修改。

相关模板：internal_templates/hand_drawn_trunk.stt、hand_drawn_branch.stt、hand_drawn_subd_branch.stt、hand_drawn_target.stt。

官方示例：samples/Learning/Vines/Hand_Drawn_Vines.spm（手绘藤蔓）、Vines_Simulation.spm（藤蔓模拟）、samples/Learning/Custom_Spines/Custom_Spines.spm（自定义脊线）。

摄影测量工作流

摄影测量（Photogrammetry）是用照片扫描真实树木得到高精度模型的技术。SpeedTree 的价值在于：把扫描件接入程序化系统，让扫描树也能有 LOD、风动和无限变体。

官方在 samples/Learning/Photogrammetry/ 下提供了完整的三套示例：

1. Oak_Photogrammetry/——把扫描的橡树接入程序化系统

文件	步骤
Target.spm	第一步：用 Target 标记对接位置
Convert_To_Trunk.spm	第二步：把扫描网格转换成树干结构
Oak_Photogrammetry_Convert_In_Place.spm	原地转换，保留原始网格位置
Stitch.spm	第三步：把扫描段与程序化枝条缝合

配套的 Mesh/ 目录里有扫描网格（Sample_Photogrammetry_Trunk.obj 与 .fbx），Converted/ 目录里有转换后的全套贴图（AO、Color、Gloss、Height、Metallic、Normal、Specular、Subsurface、VertexDisplacement 等），Stitch/ 目录里是缝合段的贴图。

2. Decal_MeshDetail/——用贴花与网格细节补充表面

配套 Knot_01、Knot_02（节疤）、LongDetail_01（长条细节）三组贴图，演示如何用 Decal 与 Mesh Detail 在扫描件上叠加细节。

3. All_Mesh_Tree_Example/——全网格树的例子

三种节点转换工具

工具	模板	作用
Convert to Trunk	convert_to_trunk.stt / convert_to_trunk_with_base.stt	把网格骨架化成可生长的树干
Convert to Branch	convert_to_branch.stt	把网格转成枝条
Convert in Place	convert_in_place.stt / convert_in_place_with_base.stt	原地转换，保持网格原始位置

Hand-drawn workflow

Procedural generation is good at trees that are “plausible overall”, but the key branches of a hero tree often need stronger shape control. That is when you use freehand mode:

1. Turn on Freehand on the toolbar.
2. Add a Spine node and drag the branch path in the viewport.
3. Use Hand Drawn:Resample to resample and smooth the hand-drawn curve.
4. Attach a Branch or Leaf Mesh under the Spine so it grows along the hand-drawn path.
5. Convert generator to hand drawn also lets you convert an existing procedural branch into a hand-drawn one and then edit it.

Related templates: internal_templates/hand_drawn_trunk.stt, hand_drawn_branch.stt, hand_drawn_subd_branch.stt, hand_drawn_target.stt.

Official samples: samples/Learning/Vines/Hand_Drawn_Vines.spm (hand-drawn vines), Vines_Simulation.spm (vine simulation), samples/Learning/Custom_Spines/Custom_Spines.spm (custom spines).

Photogrammetry workflow

Photogrammetry is the technique of scanning a real tree from photographs to obtain a high-precision model. SpeedTree's value here is bringing the scan into the procedural system, so that a scanned tree can also have LOD, wind and unlimited variants.

The official installation provides three complete examples under samples/Learning/Photogrammetry/:

1. Oak_Photogrammetry/ — bringing a scanned oak into the procedural system

File	Step
Target.spm	Step one: use a Target to mark the attachment point
Convert_To_Trunk.spm	Step two: convert the scanned mesh into a trunk structure
Oak_Photogrammetry_Convert_In_Place.spm	convert in place, preserving the original mesh position
Stitch.spm	Step three: stitch the scanned section to procedural branches

The accompanying Mesh/ directory holds the scanned meshes (Sample_Photogrammetry_Trunk.obj and .fbx), the Converted/ directory holds the full set of converted textures (AO, Color, Gloss, Height, Metallic, Normal, Specular, Subsurface, VertexDisplacement and so on), and the Stitch/ directory holds the textures for the stitched section.

2. Decal_MeshDetail/ — supplementing a surface with decals and mesh detail

It ships three texture sets — Knot_01, Knot_02 (knots) and LongDetail_01 (long detail) — demonstrating how to layer detail onto a scan with Decal and Mesh Detail.

3. All_Mesh_Tree_Example/ — an example of an all-mesh tree

The three node conversion tools

Tool	Template	Purpose
Convert to Trunk	convert_to_trunk.stt / convert_to_trunk_with_base.stt	skeletonize a mesh into a growable trunk
Convert to Branch	convert_to_branch.stt	convert a mesh into a branch
Convert in Place	convert_in_place.stt / convert_in_place_with_base.stt	convert in place, preserving the mesh's original position

规则脚本（Rules）

SpeedTree 支持用 Lua 脚本控制生成规则。安装目录里有两处相关资源：

• app_data/RuleScriptCommon.lua —— 规则脚本的公共函数库，提供 math.clamp、math.saturate、math.lerp、math.round 等工具函数。
• samples/Learning/Rules/ —— 两个示例：Conifer_Simple_Rules.spm（针叶树简单规则）与 Oak_Complex_Rules.spm（橡树复杂规则）。

规则脚本适合做“参数之间的联动”：例如让枝条粗细自动跟随长度变化，而不是分别设两个参数。对普通用户来说不是必需，但做复杂物种时能大幅减少手工调参。

投影器（Projector）

samples/Learning/Projector/Projector.spm 演示了投影器功能。投影器可以把一张贴图从某个方向投影到模型表面，用于：

• 把预先绘制好的树皮细节（如整棵树的纹理）投影上去，避免 UV 接缝。
• 投射光照信息或遮罩。
• 做快速的概念验证。

参考图（References）

samples/Learning/References/References.spm 演示了参考图的使用。做法是：

1. 把要模仿的树的照片导入为参考对象。
2. 调整参考图的比例，让它与场景单位一致。
3. 一边调参数一边对照剪影。

这是提高写实度最有效的手段之一——不要让软件里的树和真实照片脱节。

细分曲面（Subdivision Surface）

samples/Learning/Subdivision_Surface/Subdivision_Surface.spm 演示细分。配合 Subdivision 节点或 Skin:Subdivision 参数，可以把低模平滑成高模。注意每加一级细分，面数约翻四倍。

Rule scripts (Rules)

SpeedTree supports Lua scripts for controlling generation rules. The install directory has two relevant resources:

• app_data/RuleScriptCommon.lua — the common function library for rule scripts, providing utility functions such as math.clamp, math.saturate, math.lerp and math.round.
• samples/Learning/Rules/ — two examples: Conifer_Simple_Rules.spm (simple conifer rules) and Oak_Complex_Rules.spm (complex oak rules).

Rule scripts are good for linking parameters to one another: for example, making branch thickness follow its length automatically instead of setting two separate parameters. Not essential for casual users, but on complex species they greatly reduce manual tuning.

Projector

samples/Learning/Projector/Projector.spm demonstrates the projector. A projector can project a texture onto the model's surface from a given direction, which is useful for:

• Projecting pre-painted bark detail (such as a texture covering the whole tree) to avoid UV seams.
• Projecting lighting information or masks.
• Quick concept validation.

Reference images (References)

samples/Learning/References/References.spm demonstrates the use of reference images. The approach is:

1. Import a photograph of the tree you want to imitate as a reference object.
2. Scale the reference image so that it matches the scene units.
3. Adjust parameters while comparing against the silhouette.

This is one of the most effective ways to improve realism — do not let the tree in the software drift away from the real photograph.

Subdivision Surface

samples/Learning/Subdivision_Surface/Subdivision_Surface.spm demonstrates subdivision. Together with the Subdivision node or the Skin:Subdivision parameter, you can smooth a low-poly mesh into a high-poly one. Note that each level of subdivision roughly quadruples the polygon count.