[meta] Voxel ray tracing plan

[kvark]

• land the implementation - True voxelized ray traversal #218
• create tools to measure GPU time, to start optimization
• use Morton codes for the terrain buffer. This will improve data locality access patterns. Possibly, use a 2x2 texel tile as the basis (instead of the 2x1 that we have today). Probably need to update it in a compute shader.
  • alternatively, switch the terrain buffer to an R32Uint texture (storing 2 texels)
• store voxel data into a buffer as well. Use Morton codes for addressing. Pack bits into 32bit words.
• optimize voxel construction. It takes too long to load a level.
• address the portability issues, e.g. RayVoxel axis handling doesn't work on all platforms #222
• environment map for the sky
• describe the rendering approach in the blog.
• voxelized shadow rendering

[kvark]

Baseline on my Mac - the default camera of the Level binary on Fostral. Window size 2280x1524.
40ms for RT. Texture units are busy 98.7% of the time.

[kvark]

WIth #223 I'm seeing the time for RT raising to 48ms (about 20% hike). Still worth it given the reduced VRAM, and now we are mostly ALU bound, which scales better with GPUs.