Trilinear ray casting has no attenuation change

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Trilinear ray casting has no attenuation change #3551

Closed aowen87 closed 4 years ago

aowen87 commented 5 years ago

Describe the bug

Changing the attenuation has absolutely no effect when ray casting in trilinear mode. When I was updating the volume opacity for rasterization, I noticed that the trilinear opacity wasn't being calculated.

To Reproduce

Open any dataset and render a volume plot. Open up the volume attributes, switch to compositing, enable trilinear, and change the opacity attenuation to 0.

aowen87 commented 4 years ago

The attenuation is only applied to sections of the color table that have opacity < 1. Looking at the code, this seems to be intentional for this rendering method. We can fairly easily change this if needed, but I don't think it's an issue.