[Opensg-users] Diff. Material on front an back side

[<bjo...@uf...>]

Dear all,
How do use a different material and different colors on the front and back side of the polygons?
I have a simple quadrangle with colors (and secondary colors -> where are these used?") set. I
would like to render the front and back side of this polygon differently, e.g. with a general material
on the front (not using the colors on the vertices) and using the colors from the vertices on the back
side: I tried the code below. When I change values for the front side (for example setting
ColorMaterial to GL_DIFFUSE) this always seems to affect both sides.
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MaterialChunkPtr matChunk = MaterialChunk::create();
beginEditCP(matChunk);{
  // Front 
  matChunk->setDiffuse(Color4f(0.0, 1.0, 0.0, 1.0));
  matChunk->setEmission(Color4f(0.0, 0.0, 0.0, 1.0));
  matChunk->setSpecular(Color4f(0.0, 0.0, 0.0, 1.0));
  matChunk->setAmbient(Color4f(0.0, 1.0, 0.0, 1.0));
  matChunk->setColorMaterial(GL_NONE);
  matChunk->setLit(true);
  //Back
  matChunk->setBackDiffuse(Color4f(0.0, 0.0, 1.0, 1.0));
  matChunk->setBackEmission(Color4f(0.0, 0.0, 0.0, 1.0));
  matChunk->setBackSpecular(Color4f(0.0, 0.0, 0.0, 1.0));
  matChunk->setBackAmbient(Color4f(0.0, 0.0, 1.0, 1.0)); 
  matChunk->setBackColorMaterial(GL_DIFFUSE);
}endEditCP(matChunk);
ChunkMaterialPtr mat = ChunkMaterial::create();
beginEditCP(mat);{
  mat->addChunk(TwoSidedLightingChunk::create()); 
  mat->addChunk(matChunk);
}endEditCP(mat);
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I also tried to use a SimpleMaterial for the front. Then I added a MaterialChunk where I
set another SimpleMaterial as BackMaterial. I could have different material on the back
and front but found it difficult to predict the result .......
What is the right way to do what I want ? What is the secondary Color for and how do
I make use of it?

Any help would be appreciated.
Kind regards,
Bjoern Zehner