作品集

树木造型方法 

了解发生器  

speedTree的树木模型主要由两种物体构成,发生器与节点

发生器可以被认为是定义树木如何生成的规则.由发生器来描述树木,树枝和树叶.

节点是树木模型的重要组成部分.发生器根据用户定义的属性值来或者随机数来生成节点.因此,对于一棵树而言,也许是由一个发生器来生成的众多节点(也经常如此)构造的.

连接发生器

树木模型都是由根发生器产生的.例如,一棵有主干和20棵树枝构成的树,需要三种发生器,一个树发生器(每棵树都有),1个曲线生成器生成树干(曲线生成器生成树枝和树体),其它的曲线生成器生成树枝. 树干继承来自"树"发生器的发生频率1.树枝发生器则继承来自己树干的发生频率20,然后在一般编辑器中,通过将两个发生器的图标拖在一起已将他们连接起来.根据上面的设置,1棵有20根树枝的树木就显示在预览窗口了.

属性设置

在属性编辑器中,每个树木及树枝生成器的长度,半径,角度及其它相关的参数,均可在此编辑和修改.

举个例子,如果希望树木更长一些,可以设置树干发生器的"length"属性. 希望越靠近顶端的树枝越短,可以修改树枝发生器的长度曲线(绿色的). 希望给予每个分枝在长度上稍有不同, 你可以变化长度属性. 同样,你可以随时返回属性设置页修改对象的各种属性.

树发生器(右图最下面)是一棵树的根节点, 整个树的全局属性及整体行为在这里设置. 当树窗口没有任何物体被选择或者其标签被选择时树发生器的属性设置被激活

曲线控制属性的调整

如果希望某个参数在一定幅度内为变化, 就要使用曲线控制器(parent curve). 例如,属性内的绿色曲线编辑器可以让底部的树枝比其它更靠近顶端的树枝更长一些. 

而使用蓝色的曲线控制器(profile curve) 你可以编辑发生器是如何将每个属性应用到单个节点上面的----例如,一个曲线控制器能够让使树枝在一个范围内灵活变化,并有一个点来控制整个变化.  在所有的参数中共有两种曲线. 可以在属性窗口中相关属性中找到它的曲线预览图,点击它,即可以在曲线编辑窗口中修改它.

随机因子

当你制作完成了一棵树后,只需要简单的修改一下发生器的随机因子, 新的树木就可以制作出来了. 首先, speedtreecad 只有一个主因子和一个"标识"因子. 现在模型的各处都有独立的随机数发生器. 希望随机化某处的发生器,只需要点击"骰子"图标.

空间扭曲的使用

可以使用"空间扭曲"来推, 拉, 扭力, 扭曲及卷曲树一部分. 空间扭曲可以通过树木窗口和节点体系来添加到场景中. 它们支持以坐标中心为基点的操作方法---比如可以使用一个方向力来拉动所有的东西来模拟重力.

手动精确控制生成树枝

我们已经结合了重要的通过数位板(包括鼠标)手绘生成树木元素的功能. 手绘可以生成任何你想象中的树枝, 而且可以很自然得与其它部分连接. 不仅如此, 它们还可以通过贝赛尔曲线控制方式在空间中方便得进行操作. 

使节点编辑更加完美

当进行节点编辑时,适时的关闭一些节点也许可以使选择和编辑更加方便与明确. 那些不招人喜欢的树枝是从哪儿冒出来的? 选择并移开它. 这片树叶是不是离树枝太远了? 选中并删除它. 需要在一个较低的模型上进行分段? 选择并加大它的ploygonal resolution.  这种造型方式是否比原来的造型方式给予艺术家更多的控制?

在编辑节点的同时是否能同时编辑与它相关的发生器, 且由程序生成的部件仍合乎要求.

其它概念

此处涉及的是speedTree modeling 体系的基本概念. 另外还有碰撞物体自动生成, 闭塞生成, 层级细节, 风力, 物理学及其它众多工具使用speedTree更加强大, 以及对艺术家更为有用的树木模板.

原文

Modeling Method   

speedTree

Understanding "Generators"  

SpeedTree models consist primarily of two types of objects: generators and nodes.

speedtree models 

Generators can be thought of as rule sets that define how a certain part of the tree grows. There are generators that describe branches, fronds and leaves. 

Nodes are the actual components of a specific tree model. Generators create nodes based on property values and curves edited by the user, and are varied with random numbers. Therefore, a single generator may be responsible (and often is) for the creation of many of the nodes of a single tree model.

Linking Generators

Tree models are created by first setting up the generators. For example, a tree with a trunk and twenty branches growing off it would require three generators: a "Tree" generator (every tree has one), a "Spine" generator for the trunk ("Spine" generators make branches and fronds), and another "Spine" generator for the branches. The trunk would be a child of the "Tree" generator with a frequency value of 1. 

The branches generator 

would be a child of the trunk with a frequency value of 20. You can link generators together in the Generation Editor by dragging between icons. With the above setup, a tree model with a trunk node and 20 branch nodes would be visible in the tree window.

Editing Properties

The length, radii, angles, and all other parts of the trunk and branches would be edited by modifying the corresponding properties for each generator on the Property Editor. 

For example, to make the trunk longer you would increase the "Length" property of the trunk generator. To make branches near the top of the tree shorter than those at the bottom you would modify the branch generator's "Length" parent curve (the green one). To give each branch a slightly different length, you would modify the variance of the "Length" property. You can go back and edit any property later on if necessary.

The Tree Generator (at the bottom of the image to the right) is the root node of the tree, and it houses many global tree properties that govern the behavior of the rest of the tree. The Tree Generator's properties become active in the Property Editor when nothing is selected in the Tree 

Window, or when its icon is selected.

Controlling Properties with Curves

To vary a property along the length of its parent, edit the parent curve for that property. For example, within a single generator you can make the base branches longer than the branches near the tip of the parent by using the green parent curve. With the blue profile curve you can edit how each property is applied along individual nodes made by the generator – for example, a profile curve can make the radius decrease along the length of each branch so they terminate in a point. These two curve types are available for most properties. To edit them, click on the desired curve thumbnail in the Property Editor then edit the curve itself in the Curve Editor.

Randomizing Seeds

Once you have a tree made, new trees can be created by simply changing any of the generators' random seeds. Previously, SpeedTreeCAD had only a main seed and 'flares' seed. Now there are many seeds throughout the model that can be randomized independently. To randomize all of the seeds for 

a particular generator, press the 'dice' button on the Generation Editor toolbar.

Using Forces to Shape the Model

Use "Forces" to push, pull, gnarl, twist, or curl up any part of your tree. Forces can be added to the scene via the tree window and manipulated outside of the tree node hierarchy. They supply a way of manipulating things in a world-centric way – for example, a direction force can be used to simulate gravity... and it can pull in any direction!

Hand Draw Precise Branches

We've incorporated the ability to hand draw tree elements with a tablet device (or just the mouse). Hand drawn branches can be in any shape you 

can imagine, and they can be linked seamlessly with procedural content. Not only that, but they are contructed from beziere spline control points that are easy to manipulate in world space. Check out the hand drawing documentation for more details.

Get It Perfect with Node Editing

Once the tree is reasonably close to what you're looking for individual nodes can be selected and edited explicitly. Don't like where a branch is? 

Select it and move it. A leaf is sticking out too far? Select it and delete it. Need more segments on a low branch? Select it and increase the polygonal resolution. It is this type of editing that gives artists much more control over the modeling process than exists with typical procedural modeling approaches. Any node edited in this manner can still be modified by its associated generator and is still eligible to have procedural components grow off of it.

Other Concepts

That covers the basic idea behind SpeedTree's modeling philosophy. Added to this concept are automatic collision object generation, ambient occlusion, level of detail, wind, physics and a host of other tools to make SpeedTree the most powerful and artist friendly tree modeling package available.