[vtkusers] Problems while rendering of large volumes

[ianl]

Hi Aashish,

I have managed to 'fix' this by cutting and pasting the
vtkOpenGLGPUVolumeRayCastMapper::GetReductionRatio code from the old OpenGL
branch, and deleting the code in the header that returns 1 for each
dimension. This does not compile as-is, but the only change that is needed
is to pass GL_MAX_TEXTURE_SIZE to glGetIntegerv() rather than
vtkgl::MAX_3D_TEXTURE_SIZE. This seems to work fine, but is probably not the
'correct' way to sort this out. It does seem, however that the code is
independent of the vtkGPUInfo class, so may be easier to fix properly than
it first appears.

As an aside, it looks like someone on the slicer mailing list had a similar
issue, so we are not alone in having this problem.

See:
https://discourse.slicer.org/t/dicom-volume-rendering-max-3d-texture-size-error/1066

Hope this helps someone,
Ian Lindsay.



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