file: 2013-08-14_maya_blendshape.md
title: maya blendshape
date:
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最近接触了一点maya blendshape api programming, 稍微记录一下。
先说明一个特点，当drag一个cube or sphere物体的时候，会生成
To create a simple blendshape example,
Polygon mode, create a cube, we have
Select cube1, Shift+D, we have
Select cube1, Shift+D, we have
Select cube3 first, then shift+select cube2, then shift+select cube1,
Animatioin mode, menu Create Deformer > BlendShape, we have a blendshape deformer node, for example called blendShape1.
cube1 is called source shape for this blenshape.
cube2 and cube3 are as target shapes for this blendshape.
select cube1, menu Windows > Connections, we see the connections of these nodes.
**Maya/Fbx API Table.**
| source | blendshape | channel | target |
|---|---|---|---|
| MObject | MFnBlendShapeDeformer | Target Weight slider | MObject |
| FbxGeometry | FbxBlendShape | FbxBlendShapeChannel | FbxShape |
有关target weight slider的注意事项:
+ 一个blendshape可以有多个target weight slider, 每一个slider中可以是一个or多个target shapes, 取决于In-Between off/on.
+ 每一个target weight slider 有一个数值叫target weight (value) 表示target shapes对source的effect.
+ 每一个target weight slider 有一个名字target weight or target weight slider name or name of target weight. 这个name是用transform node的名字，例如上述例子的两个target weights的名字分别是pCube2 and pCube3. tricky的是这个名字可以被改掉, 改成whatever u like, 例如这里改成pCube2x. 于是在code里面就有个问题了，给出一个target weight name, how to find out the target shape (or the transform node of the target shape) associated with this target weight name?
一些调试的MEL commands:
```
objExists pCube2
objExists |pCube2
objExists pCube2|pCubeShape2
objExists pCubeShape2
objExists |pCubeShape2
objExists blendShape1.pCube2x;
// Results: 1 //
blendShape -q -g blendShape1;
// Result: pCubeShape1 // the source shape's name, not transform node's name.
blendShape -q -target blendShape1;
// Result: pCube2 pCube3 // the target shape ‘s transform node’s name.
blendShape -q -t blendShape1;
// Result: pCube2 pCube3 // the flag -target is the same as -t
blendShape –q –weightCount blendShape1;
// Result: 2 // 这里返回的数字应该就是刚好上面targets数目
blendShape -q -w blendShape1;
// Result: 0.5 0 // 每一个target weight's value.
listAttr -sn blendShape1.weight[0];
// Result: pCube2x //
listAttr -m blendShape1.w;
// Result: pCube2x pCube3 // names of target weight, not the name of target shape or transform node.
aliasAttr -q blendShape1;
// Result: pCube2x weight[0] pCube3 weight[1] // 对应关系
aliasAttr -q blendShape1.pCube2x;
// Result: pCube2x //
aliasAttr smile blendShape1.weight[0];
aliasAttr smile blendShape1.w[0]; // weight[0] == w[0]
// Result: 1 // 把weight[0]改名为smile, 而不是上面的pCube2x了.
setAttr blendShape1.pCube2x 0.5; //成功, 调target weight slider的value.
setAttr "blendShape1.pCube2x" 0.8; //成功, 调target weight slider的value.
setAttr blendShape1.smile 0.6; // Succeed,
setAttr blendShape1.w[0] 0.7; // Succeed, w[0] == weight[0] has been renamed as smile.
```
在Script Editor中输入 help
```
MString command = "objExists pCube1";
int result = 0; // false;
MStatus status = MGlobal::executeCommand(command, result);
```
updated about getting the target shapes from the blendshape deformer node.
updated 2013/10/11. blendShape是线性操作，deformed result = source * (1 - target_weight) + target * target_weight;
source and target可以说shape mesh, 也可以是别的blendshape deformation node的结果。
udated 2013/10/12. 遇到一个使用objExists mel command的bug. 假如Face + FaceShape是面部的transform + shape nodes, 它在DAG中的path是:
|man|head_group|Face|FaceShape
那么在Script Editor里面执行:
objExists |Face
的结果是什么呢? false, 找不到|Face ? 场景中不是明明有Face这个node的吗? 试试执行:
objExists Face
结果是true。 原来不是找不到Face, 而是找不到|Face. 两者有什么区别? |Face表示这个face node是直接在root下面. 所以我觉得用objExists命令还是别加|为好. 在maya scene graph的资料中有提到|.
MFnBlendShapeDeformer::addTarget(base shape, channel/target weight index, target shape, weight value);
可否多次add相同的targets呢？还是每次add target之前先判断假如已经有得话就先removeTarget呢?
Target weight上的connection (MPlug的应用)
----
来一个简单的例子。建一个blendShape1(cube1 as source, cube2 and cube3 as target shapes, rename the weight to be weight1 and weight2)。
blendshape1.weight1 是一个plug的名字，其实这个weight1也同时是对应target slider的名字。上面提到可以用listAttr and aliasAttr来找有什么plugs和改它们的名字. 下面来看怎么获得obtain这些sliders/weights:
```
// mel commands
blendShape -q -wc blendShapeName; // return the weight count;
listAttr -m blendShapeName.w; // return all the names of weights.
aliasAttr -q blendShapeName; // return all the weights' names and associated weight[i]
// c++ code
unsigned int iWeightCount = MFnBlendShapeDeformer::numWeights();
MFnBlendShapeDeformer::weightIndexList( MIntArray &indexList );
assert( iWeightCount == indexList.length() );
MPlug plugs = blendShapeNode.findPlug("weight", &status);
assert( iWeightCount == plugs.numElements() ); // one weight <-> one "weight" plug
for (unsigned int i = 0; i < iWeightCount; ++i)
{
MPlug weightPlug = plugs[i]; // we can get the slider/weight name.
// indexList[] is only a small set of the indices of a very large weight array[],
// some items of the big weight array[] are not used, some items are
// deleted and invalid if some targets are removed from weight.
const int iWeightIndexOfWeightArray = indexList[i];
// this iWeightIndexOfWeightArray can be used to get the weight value and targets.
...
// btw, one weightPlug / slider / weight <--> one FbxBlendShapeChannel
// the target shapes of this channel become some objects of FbxShape.
}
```
一般情况下我们是通过拖动这slider来调blendshape的效果。对应的mel and c++ code:
```
setAttr "blendshape1.weight1" 0.5
weightPlug.setDouble( 0.5 ); // MPlug weightPlug; weightPlug.name() == "blendshape1.wieght1";
```
也可以把别的值connect到这个target weight上来, 例如通过动画animation或者locator等控制target weight的值的变化。每一个connection是由source plug and destination plug组成的. 在上面的blendShape1例子上增加一点:
建一个plane1, 打开Window > Node Editor 把plane1的translateX连到blendShape1.weight1, 把plane1的translateY连到blendShape1.weight2, UI上这两个sliders都变成黄色了, DG窗口中blendShape1这个node的形状也从长方形变成的菱形.
上面的过程其实我们建立了两个connections. 其中一个connection是 (pPlane1.translateX, blendshape1.weight1)，其中pPlane1.translateX称为source plug, blendShape1.weight1称为destination plug.
下面的代码显示怎么获得一个blendShape的plug, 以及这些plug的连接connections:
```
// given MFnDependencyNode blendShapeNode, and MStatus status;
MPlug plugs = blendShapeNode.findPlug("weight", &status);
for (unsigned int i = 0; i < plugs.numElements(); ++i)
{
MPlug weightPlug = plugs[i]; // as destination plug for connection.
MPlugArray inPlug; // as source plug for connection.
weightPlug.connectedTo(inPlug, true, false);
for (unsigned int i = 0; i < inPlug.length(); ++i)
MGlobal::displayInfo(inPlug[i].name() + " + " + weightPlug.name()); // for debug.
}
// mel command below:
listAttr -m blendShape1.w;
// for example returns weight1 weight2 ...
connectionInfo -sourceFromDestination blendShape1.weight1;
// for example returns pPlane1.translateX, the source of the connection (string, empty if null).
connectionInfo -destinationFromSource pPlane1.translateX;
// for example returns blendShape1.weight1
```
假如这个target weight对应的模型target shape被removeTarget了, 那些connection还在吗？不在了，可能是副作用side effect。 假如重新把模型addTarget回blendShape1，还想重新把那些断开的connection重新连上呢，否则之前key的动画等都失效了/
```
// target shape is removed from this blendshape for some reason.
// target shape is re-added into the blendshape. we want to
// restore those connections before. how to do this?
MString commandString = "connectAttr " + inPlug[i].name() + " " + weightPlug.name();
MGlobal::executeCommand(commandString, true); // true: display the result.
```
上面的代码中我用了connectAttr这个mel command, 貌似MDGModifier::connect(,)也有相似的功能，但网上查阅时候这个东西一般是放到某个custom command class里面用的，而且还要自定义undo/redo的函数，我还没试过。相比而言，直接用mel就没有这些担心。本来UI上的操作给我的感觉就是用相应的参数来调用底下的mel commands (Script Editors往往显示这些命令历史), mel command再底下当然可能是用C++ 函数XX在实现的。
UI operation -> mel command -> c++ XX function (not exposed to user);
而给出一些maya c++ api，可能也能实现某mel命令所做的事，毕竟假如api够用的话就能把XX函数都模拟一次，但是可能有些bugs. 所以是不是这样比较好呢:
mel command有的，就MGlobal::executeCommand(...); mel command实现起来不方便 or 实现不了的(有吗？例如自定义的某些操作?) 才用maya api来做.
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