Tomviz MacOSX Cannot Render More Than 2 Volumes at Same Time

[jtschwar]

Describe the bug
A clear and concise description of what the bug is.

Whenever I try to render three separate volumes for chemical tomography I get an error saying the shader failed to compile. See below:

ERROR:
In /Users/kitware/dashboards/buildbot-slave/tomviz-bigmac-osx-shared-release_clang_osx10_9_superbuild/build/paraview/src/paraview/VTK/Rendering/OpenGL2/vtkShaderProgram.cxx,
line 498 vtkShaderProgram (0x600003077c00): Links failed: ERROR: Implementation limit of 16 active fragment shader samplers (e.g., maximum number of supported image units) exceeded, fragment shader uses 17 samplers

ERROR:
In /Users/kitware/dashboards/buildbot-slave/tomviz-bigmac-osx-shared-release_clang_osx10_9_superbuild/build/paraview/src/paraview/VTK/Rendering/VolumeOpenGL2/vtkOpenGLGPUVolumeRayCastMapper.cxx, line 2699
vtkOpenGLGPUVolumeRayCastMapper (0x7fa85a7a3e30): Shader failed to compile

I've tested this three separate Mac systems and the error consistently appears.

To Reproduce
Steps to reproduce the behavior:

1. Select the Sample Reconstruction Three Times and Apply the Volume Module to each instance as shown below: (This error appears with separate datasets as well).

Expected behavior
A clear and concise description of what you expected to happen.

I should be able to render all three volumes and apply separate color maps, etc. As Discussed on the RGB Volumes feature on the Documents.

Screenshots
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Desktop (please complete the following information):

• Operating system: macOS 12.2.1
• Tomviz version: 1.10.0-154-ga5eee93a

Hardware (please complete the following information):

• Device: Macbook Pro (2021) and iMac (2019)
• Graphics card: Radeon Pro 570X

Additional context
Add any other context about the problem here.

[psavery]

Looks like this specifically happens with the "Allow Multi Volume" box checked, and is probably specific to the multi volume features.