Blend multiple volumes/meshes

There might be some way to actually combine multiple volumes, either by overlapping or by actually blending them in the shader

The issue proposes combining multiple volumes or meshes, either through overlap or shader-based blending. No files, tests, or rendering entry points are identified, so begin by locating the volume and mesh rendering code and its shaders. Done should include a defined blending approach and a demonstrated result for multiple inputs.

Written by the indexing model from the issue text.