Fix GL_INVALID_OPERATION in vtkFramebufferPass under GLES 3.0

Jaswant Panchumarti (Kitware)requested to merge
jaswant.panchumarti/vtk:gles-framebuffer-pass into master
  • WebGL2 (GLES 3.0) forbids blitting to a multisampled draw framebuffer.
  • This commit detects such situation and uses the vtkTextureObject::CopyToFrameBuffer() method as a workaround. This should give similar results to the glBlitFramebuffer call under desktop OpenGL.

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