8 Responses to “Chapter 9”

1. Hi,

   Im currently working through this book (loving the book.. ) and even started to experiment with Maya API. Im a little stuck and was wondering if someone could please help me out. Im writing a script to find the average edge length but I cant seem to get it in world space. “getLength(doublePtr, NOT SURE WHAT I NEEDS HERE)”

   import maya.cmds as mc
   import maya.mel as mm
   import maya.OpenMaya as om

   #
   #GET POLYGON SELECTION
   selection = om.MSelectionList()
   om.MGlobal.getActiveSelectionList( selection );
   iter = om.MItSelectionList ( selection, om.MFn.kGeometric );

   while not iter.isDone():
   dagPath = om.MDagPath()
   iter.getDagPath( dagPath )
   mObj = om.MObject()
   iter.getDependNode( mObj )
   dagPathHandle = dagPath.fullPathName()
   iterEdge = om.MItMeshEdge( mObj )

   while not iterEdge.isDone():
   edgeIndexListHandle =[]
   edgeIndexListHandle.append(iterEdge.index())
   print edgeIndexListHandle

   util = om.MScriptUtil()
   doublePtr = util.asDoublePtr()
   iterEdge.getLength(doublePtr)
   length = om.MScriptUtil.getDouble(doublePtr)
   print length
   iterEdge.next()
   iter.next()

   francois said this on February 12, 2012 at 4:51 pm | Reply

   • Hi Francois,

     Looks like the second parameter for MItMeshEdge.getLength() is an MSpace (enum) value, whose default value is object space. To do world space, you should try passing om.MSpace.kWorld.

     Adam said this on February 12, 2012 at 7:20 pm | Reply

2. When i try to pass om.MSpace.kWorld I get the following error:

   RuntimeError: (kInvalidParameter): Must have a DAG path to do world space transforms #

   Im a bit stuck on how to get this

   francois said this on February 13, 2012 at 1:56 pm | Reply

   • When you initialize your MItMeshEdge iterator, you must pass it an MDagPath (dagPath) rather than an MObject (mObj). When you initialize with an MObject, there may be multiple paths to the object (e.g., if it is instanced) and so it needs a unique DAG path in order to know where it is in world space.

     Adam said this on February 13, 2012 at 4:24 pm | Reply

3. Thanks Adam that did the trick

   francois said this on February 14, 2012 at 7:17 pm | Reply

4. I ran into an issue using the the API and I need some help.

   I used MFnSkinCluster.getPointsAffectedByInfluence to get the vertices affected by an influence. When I print out the selection list of the points it says that there is only one point even though I know that influence affects more points. here is the script I used:

   import maya.OpenMaya as om
   import maya.OpenMayaAnim as oma

   om.MGlobal.clearSelectionList()
   om.MGlobal.selectByName(‘skinCluster2’)

   infs = om.MDagPathArray()

   sList = om.MSelectionList()
   om.MGlobal.getActiveSelectionList(sList)
   node = om.MObject()
   sList.getDependNode( 0, node )

   skin = oma.MFnSkinCluster(node)
   numInfs = skin.influenceObjects(infs)

   skinPath = om.MDagPath()

   index = 0
   skin.getPathAtIndex(index,skinPath)

   geo = om.MItGeometry(skinPath)

   weights = om.MDoubleArray()
   pointsInfl = om.MSelectionList()
   skin.getPointsAffectedByInfluence(infs[3], pointsInfl, weights)
   print ‘pointsInfl %s’% pointsInfl
   print pointsInfl.length()

   serena said this on June 29, 2012 at 9:15 am | Reply

5. Hi,

   I’m writing a simple deformer which I need it to get and set vertex positions in world space.

   I’m getting the same error francois. But the MItMeshVertex has been created automatically by the deform method so how can we pass it a MDagPath?

   Here is what I’ve accomplished so far:

   
import maya.OpenMaya as om
import maya.OpenMayaMPx as mpx
import sys

   nodeName = 'ehm_flattenDeformer'
   nodeId = om.MTypeId( 0x0011E182 )

   class ehm_flattenDeformer( mpx.MPxDeformerNode ):

   def __init__( self ):
   mpx.MPxDeformerNode.__init__( self )

   def deform( self, dataBlock, geoItr, matrix, index ):

   # 0. get deformer input
   input = mpx.cvar.MPxDeformerNode_input

   # 1. Attach a handle to input Array Attribute.
   inputHandle_array = dataBlock.inputArrayValue( input )

   # 2. Jump to particular element
   inputHandle_array.jumpToElement( index )

   # 3. Attach a handle to specific data block
   inputHandle_element = inputHandle_array.inputValue()

   # 4. Reach to the child - inputGeom
   inputGeom = mpx.cvar.MPxDeformerNode_inputGeom
   inMeshHandle = inputHandle_element.child( inputGeom )

   # 5. get Mesh
   inMesh = inMeshHandle.asMesh()

   # Envelope
   envelope = mpx.cvar.MPxDeformerNode_envelope
   envelopeHandle = dataBlock.inputValue( envelope )
   envelopeValue = envelopeHandle.asFloat()

   # deform
   while not geoItr.isDone():

   pointPosition = geoItr.position( om.MSpace.kWorld )
   pointPosition.y *= (1-envelopeValue)
   geoItr.setPosition( pointPosition, om.MSpace.kWorld )

   geoItr.next()

   def nodeCreator():
   return mpx.asMPxPtr( ehm_flattenDeformer() )

   def nodeInitializer():
   pass

   def initializePlugin( mObj ):
   plugin = mpx.MFnPlugin( mObj, 'Ehsan HM', '1.0', 'any' )
   try:
   plugin.registerNode( nodeName, nodeId, nodeCreator, nodeInitializer, mpx.MPxNode.kDeformerNode )
   except:
   sys.stderr.write( 'Faild to load plugin: %s' % nodeName )

   def uninitializePlugin( mObj ):
plugin = mpx.MFnPlugin( mObj )
try:
plugin.deregisterNode( nodeId )
except:
sys.stderr.write( 'Faild to unload plugin: %s' % nodeName )

   Ehsan said this on November 14, 2013 at 9:10 am | Reply

   • Hi Ehsan,

     It’s the same problem, unfortunately. Imagine you have a shape node of some kind connected to your deformer. This shape might be instanced by 100 different transforms, so you’d need to somehow specify which you want to use for world space. However, you don’t really want to start looking outside your node (i.e. traversing the DAG) to get a path, as you could trigger all kinds of other computation in the graph. A safe approach could be to have your node take local and parent matrices as additional input, which you then use to calculate your positions for the iterator, and then make sure your accompanying command or other setup utility attaches a selected object’s matrix/parentMatrix when the node is created.

     Adam said this on November 28, 2013 at 8:18 pm | Reply