geomShader

geomShader.py是使用API编写maya材质的简单的例子，是的API也可以用来写自定义材质。
为了方便我就直接复制帮助文档里的geomShader.py内容过来，加入适当的注释，要试用的话可以直接加载devkit\plug-ins\scripted中的geomShader.py，你会在Hypershade的utility栏下的color中找到"spGeomShader"

import sys
import maya.OpenMaya as OpenMaya
import maya.OpenMayaMPx as OpenMayaMPx

# 材质的名称
kPluginNodeName = "spGeomShader"
# 材质所在的位置
kPluginNodeClassify = "utility/color"
# 材质节点的类型ID
kPluginNodeId = OpenMaya.MTypeId(0x8700E)

# 定义材质类
class geomShader(OpenMayaMPx.MPxNode):
        def __init__(self):
                OpenMayaMPx.MPxNode.__init__(self)

                # 节点属性
                aOutColor = OpenMaya.MObject()
                aPoint = OpenMaya.MObject()
                aScale = OpenMaya.MObject()
                aOffset = OpenMaya.MObject()

        def compute(self, plug, block):
                if plug == geomShader.aOutColor or plug.parent() == geomShader.aOutColor:
                        # 初始化结果变量
                        resultColor = OpenMaya.MFloatVector(0.0,0.0,0.0)
                        
                        # 获取属性的数值
                        point = block.inputValue( geomShader.aPoint ).asFloatVector()
                        scale = block.inputValue( geomShader.aScale ).asFloatVector()
                        offset = block.inputValue( geomShader.aOffset ).asFloatVector()

                        # 计算出我们需要的结果
                        resultColor.x = point.x * scale.x + offset.x
                        resultColor.y = point.y * scale.y + offset.y
                        resultColor.x = point.z * scale.z + offset.z

                        # 将结果赋予输出属性，并更新节点
                        outColorHandle = block.outputValue( geomShader.aOutColor )
                        outColorHandle.setMFloatVector(resultColor)
                        outColorHandle.setClean()
                else:
                        return OpenMaya.kUnknownParameter

# 节点创建函数
def nodeCreator():
        return OpenMayaMPx.asMPxPtr( geomShader() )

# 节点初始化函数
def nodeInitializer():
        nAttr = OpenMaya.MFnNumericAttribute()

        try:
                # 给节点创建pointObj属性
                geomShader.aPoint = nAttr.createPoint("pointObj", "p")
                nAttr.setStorable(0)
                nAttr.setHidden(1)

                # 给节点创建scale属性
                geomShader.aScale = nAttr.createPoint("scale", "s")
                nAttr.setKeyable(1) 
                nAttr.setStorable(1)
                nAttr.setReadable(1)
                nAttr.setWritable(1)
                nAttr.setDefault(1.0, 1.0, 1.0)

                # 给节点创建offset属性
                geomShader.aOffset = nAttr.createPoint("offset", "o")
                nAttr.setKeyable(1) 
                nAttr.setStorable(1)
                nAttr.setReadable(1)
                nAttr.setWritable(1)

                # 给节点创建outColor属性
                geomShader.aOutColor = nAttr.createColor("outColor", "oc")
                nAttr.setStorable(0)
                nAttr.setHidden(0)
                nAttr.setReadable(1)
                nAttr.setWritable(0)

        except:
                sys.stderr.write("Failed to create attributes\n")
                raise

        try:
                # 将所创建的属性添加给节点
                geomShader.addAttribute(geomShader.aPoint)
                geomShader.addAttribute(geomShader.aScale)
                geomShader.addAttribute(geomShader.aOffset)
                geomShader.addAttribute(geomShader.aOutColor)
        except:
                sys.stderr.write("Failed to add attributes\n")
                raise

        try:
                # 建立属性之间的影响关系
                geomShader.attributeAffects (geomShader.aPoint, geomShader.aOutColor)
                geomShader.attributeAffects (geomShader.aScale, geomShader.aOutColor)
                geomShader.attributeAffects (geomShader.aOffset, geomShader.aOutColor)
        except:
                sys.stderr.write("Failed in setting attributeAffects\n")
                raise


# initialize the script plug-in
def initializePlugin(mobject):
        mplugin = OpenMayaMPx.MFnPlugin(mobject)
        try:
                mplugin.registerNode( kPluginNodeName, kPluginNodeId, nodeCreator, 
                                        nodeInitializer, OpenMayaMPx.MPxNode.kDependNode, kPluginNodeClassify )
        except:
                sys.stderr.write( "Failed to register node: %s" % kPluginNodeName )
                raise

# uninitialize the script plug-in
def uninitializePlugin(mobject):
        mplugin = OpenMayaMPx.MFnPlugin(mobject)
        try:
                mplugin.deregisterNode( kPluginNodeId )
        except:
                sys.stderr.write( "Failed to deregister node: %s" % kPluginNodeName )
                raise

值得注意的是添加属性的方法，和注册插件的方法的变动
在线版本
http://download.autodesk.com/us/maya/2011help/API/geom_shader_8py-example.html