Unstructured Grid Volume Rendering with OSPRay is almost transparent
See here for more info:
Problem: when I use the volume rendering and OSPRay, the data will disappear. test.vtk
Answer form Kenneth Moreland:
It looks like when ParaView uses the projected tetrahedra method for volume rendering (the default for unstructured data like test.vtk) the OSPray render is rendering the volume much more transparent than OpenGL. I don’t know why, but there are a couple things you can do to correct it.
One thing you can do is to change the volume rendering mapper from Projected tetrahedra to Resample To Image
. The image volume rendering seems equivalent between OSPray and OpenGL. You may have to play with the sampling dimensions to get a good image.
If you need the details of the unstructured grid and must render it directly, you can alternately lower the Scalar Opacity Unit Distance
parameter. (I don’t know why OSPray is interpreting this parameter differently than OpenGL. This might be related to bug #18890, but I’m not sure.) If you crank that value down to 0.1, I can see the middle (opaque) part of the volume clearly. That said, the results look very speckled. OSPRay must be using some kind of trapdoor transparency for rendering. You can correct that by increasing the Progressive Passes
and/or Samples Per Pixel
parameters for OSPRay. That will increase the rendering time though.