[Maya2osg-users] Blend Shapes and Geometry Export

[Peter W. <pp...@cg...>]

Hi all,

wanna give some information about the current geometry export and the 
required steps to implement deformers like skinClusters and blendShapes. 
We should also implement normal Maya Clusters, as they are a fast and 
usefull Character utility.

The current mesh exporter converts maya poly mesh into a VBO. Only 
osg::DrawElementsUByte( osg::PrimitiveSet::TRIANGLES ) are supported 
right now, all non triangle meshes get triangulated internally.
In this proces, Vertices with multiple Normals ( Hard Edges ) or 
multiple UVs are duplicated, so the osg vertex count and IDs and don't 
correspond to the Maya vertex count and IDs in most of the cases. All 
Vertex Attributes are stored inside a Vertex Structure, and it has a 
field for the original Maya Vertex ID, which I will use for skinning.
One Issue here is, that the Shape Orig of a Maya deformation chain does 
not have a shader attached, and does not necessarily need to have the 
same UVs or Normals as the resulting Mesh. The same is true for all the 
BlendShape Targets. The only attributes that are considered are 
VertexPositions and Normals ( there is a flag in 
osgAnimatin::MorphGeometry whether to morph Normals as well ).

This means, that when exporting a deforming Mesh, the ShapeOrig, the 
resulting Shape and in the case of BlendShapes the Blend Targets should 
be exported simultaneously.
Now the Vertex Atributes Structure is handy, as when all the 
osg::VertexArrays of the resulting mesh are generated, the required ones 
( Position and Normals ) can be duplicated, and the corresponding Values 
can be accessed through the originla VertexID Attribute in the Vertex 
Structure, or even more confortable in the mVertexToVBOIndices variable, 
which is a std::Vector ( corresponding to Maya IDs ) of std::Vectors ( 
the VBO IDs that refer Maya ID ).

One more Issue. Now, it is possible to have shaders per Face attached, 
the exporter will capture all faces attached to one shader into one 
osg::Geometry, as to my understanding this is the lowest possible option 
to attach a osg::StateSet. This means one Maya Mesh can get Split up 
into multiple osg::Geometries. If this Mesh is a BlendShape, then we 
need to export as many MorphGeometries as Shaders are attached, and this 
leads to a new overhead of managing and connecting ( or duplicating ? ) 
animations.

That's it for now I guess.

Cheers, PP