VTK 7.1 vtkOpenGLGPUVolumeRayCastMapper will not refresh volume when the first frame is a pure color

Environment:

• Ubuntu 14.04.5 64bit
• VTK 7.1.0

vtkOpenGLGPUVolumeRayCastMapper will not refresh volume when the first volume frame is a pure color.

I have uploaded the demo code to https://github.com/Honghe/Demo_vtk_volume_not_refresh
And the code in the line ViewPort1.cpp#L62 is the toggle. If set the value to the same scalar, the subsequent volume data change will not be render.

The following image is a demo: the left sub image is set to pure color at the first frame, and the right sub image is set to random colors at the first frame.