Speculars with vtkGPUVolumeRayCastMapper are not Phong's
Hi all !
I'm a little confused by the way the speculars are handled with vtkOpenGLGPUVolumeRayCastMapper. The diffuse and ambient components are ok, but the way the specular components are computed doesn't look like Phong's shading model (or any shading model I know). So I tested its effect on a volumetric sphere and set the ambient/diffuse contributions to 0, and the results I get don't really look like speculars. The code I used is here. I used a unique positional light represented by a red dot, in order to study the shading model. For example, when the light is between the camera and the sphere center, the specular is null, which is surprising. There's another example below (the red dot is at the light position).
Is it intended ? Otherwise, I can open an MR to change the specular formula in the mapper. Thanks !