Shader rework for terrain polygon clipping

[mzschwartz5]

Description

This PR is the 4th installment in the effort to reimplement Clipping Polygons on top of the vector data pipeline -- specifically, for terrain (3d tiles and models to come).

In this PR, I wire up the vector-clipping texture uniforms and make the shader changes to actually use them. Thus, as of this PR, terrain clipping actually operates via the vector shaders!

And just look at the difference in quality:

Vector-based clipping:

SDF-based clipping:

Issue number and link

https://github.com/iTwin/cesiumjs-web3d-internal/issues/34

Testing plan

A sandcastle that uses a star shaped polygon to clip the globe (feel free to add terrain and test that too). Use the slider or input field to change the scale of the star and ensure it's crisp at all scales.

Dynamic clipping collection -- this one tests adding and removing clipping polygons from a collection. On this PR branch, the 3D tiles option still uses the SDF approach and will not render crisply.

Standard clipping regions sandcastle -- basic functionality check

The clipping performance dev sandcastle is another good one for testing various numbers (of polygons, points per polygon, spacing, etc.). NOTE: in this PR, I have not yet removed the SDF code paths. So the performance of clipping will appear the same or worse, as the SDF textures are still being generated.

Author checklist

• I have submitted a Contributor License Agreement
• I have added my name to CONTRIBUTORS.md
• I have updated CHANGES.md with a short summary of my change
• I have added or updated unit tests to ensure consistent code coverage
• I have updated the inline documentation, and included code examples where relevant
• I have performed a self-review of my code

AI acknowledgment

• I used AI to generate content in this PR
• If yes, I have reviewed the AI-generated content before submitting

If yes, I used the following Tools(s) and/or Service(s):

If yes, I used the following Model(s):

PR Dependency Tree

• PR Clipping polygon buffer migration #13623
  • PR Vector Textures for Polygon Clipping #13635
    • PR Clipping texture plumbing #13636
      • PR Shader rework for terrain polygon clipping #13637 👈
        • PR Remove SDF polygon clipping from Globe #13638
          • PR Model clipping rework foundation #13641
            • PR Model polygon clipping shader impl #13647
              • PR Remove polygon clipping sdf path #13654
                • PR Clipping Polygon Holes #13660
                  • PR ClippingPolygon immutable positions (performance) #13665

This tree was auto-generated by Charcoal

[github-actions]

Thank you for the pull request, @mzschwartz5!

✅ We can confirm we have a CLA on file for you.

[mzschwartz5]

Here, I'm mainly just factoring out some code into a reusable function (vectorCellRange), and adding a new function vectorClip for the actual clipping flow. Two notes:

1. You'll notice vectorClip is pretty similar structurally to vectorPolygonRender. It's possible they could be refactored to share even more code and avoid repeating ourselves. I did try this, but it was kind of ugly and added a little performance overhead. Decided to leave as-is.
2. I added a couple uniforms for clipping. Ideally, I think a better solution would be for this file to not explicitly declare uniforms, and to have the functions be parameterized to accept them. I'm leaving that as a TODO; it's good enough as-is.

[mzschwartz5]

This is the meat of this PR: here, we actually switch over from the old SDF-based clipping function, to the new vector-based clipping function.