Gaussian Splats 0.1

[emilk]

What

• Part of Support for NeRFs and Gaussian splatting #4529

MVP for gaussian splats.

Can load .ply files as found on https://poly.cam/tools/gaussian-splatting and display them without the gaussian transparency:

Implementation

This adds a scale and rotation to points, which are then used to generate splats in the vertex shader (where the 3x3 covariance matrix is calculated)

Blockers for merging

• Use the same Points archetype
• HalfSize is not the right component for splat scale
  • Maybe encode splat size as a GaussianStdDev3 component or something?
• Picking for splats
• Separate PointSplatBuilder
• Separate point_splat.wgsl
• Decide on point_cloud.rs - split, or reuse?

Shortcomings

• No transparency sorting
• No actual gaussian blur
• No support for view-dependent color using Spherical Harmonics
• Gaussians must be decomposed in rotation+scale (no 3x3 covariance support)
• Uses a lot of VRAM
• The .ply loader is really slow

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using newly built examples: app.rerun.io
  • Using examples from latest main build: app.rerun.io
  • Using full set of examples from nightly build: app.rerun.io
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG

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