[vtkusers] Re: vtkOpenGLVolumeTextureMapper3D: color problems, please help

[Michael Knopke]

Hi Frank,

I don't think I fully understand your problem, but maybe this helps:

In OpenGL you can exclude certain values from rendering (not from interpolation). This is done within the alpha-test stage. The function is:

glAlphaFunc (GL_GREATER, (GLclampf) 0);  // you can find this in the vtkOpenGLTextureMapper3D.cxx file

you can use GL_LESSER and GL_EQUAL as well.

But in this case it is the actual opacity a fragment has got and not a density value. So in this case it discards everything below 0 opacity (because it would not contribute to the blending anyway). Maybe you can use that.

But I think your opacity or colorfunction is not set correct. I don't think it has anything to do with the sampledistance, this only defines how many planes you get for blending (quality).

can you post your opacity and color function? I never had this problem you describe.

Regards

Michael

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