Paul Martz wrote:
In an ideal world, vertex attributes would work more like uniforms.
You'd specify a shader variable name along with your array, and OSG
would determine the slot number to use in the call to OpenGL.
For whatever reason, it wasn't implemented that way, and instead you
need to specify the slot number yourself. To complicate things,
apparently OSG has reserved certain slot numbers for itself in order to
support the old GL1/2 special case vertex attributes (like
setVertexArray, setNormalArray, setColorArray, etc).
Digging through the code to divine exactly how you should deal with this
at the application level is somewhat difficult. A good place to start
would be grepping the source for the GL calls related to vertex attributes.
I don't know if this is still true or not, but the NVIDIA drivers used
to "alias" the generic vertex attributes with the traditional
fixed-function attributes, so, for example, if you used normals in your
geometry, you couldn't use generic attribute 2 (it was occupied by the
normals).
The attributes mapped up like this (from the GL_ARB_vertex_program
specification):
0 vertex position glVertex
1 vertex weights 0-3 glWeightARB, VertexWeightEXT
2 normal glNormal
3 primary color glColor
4 secondary color glSecondaryColorEXT
5 fog coordinate glFogCoordEXT
6 - -
7 - -
8 texture coordinate set 0 MultiTexCoord(TEXTURE0, ...)
8+n texture coordinate set n MultiTexCoord(TEXTURE0+n, ...)
I expect this restriction has gone away with the G80-class (i.e.: OpenGL
3 capable) hardware and higher, but I haven't checked to be sure.
--"J"
_______________________________________________
osg-users mailing list
[email protected]
http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
