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Improve numerical robustness in path tiling #401

Merged
merged 7 commits into from
Nov 2, 2023
Merged

Improve numerical robustness in path tiling #401

merged 7 commits into from
Nov 2, 2023

Commits on Nov 1, 2023

  1. Add test scene to trigger numerical robustness issues 

    This test scene contains a number of subpaths that contain line segments aligned to the grid, or that cross grid corners. These trigger one-pixel artifacts with the multisampled rendering modes, and are now correct with area antialiasing.
    @raphlinus
    raphlinus committed Nov 1, 2023
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  2. Change to tile-relative segment coordinates 

    WIP. Currently works but no cleanup.
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    raphlinus committed Nov 1, 2023
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  3. Move numerical robustness into tiling 

    Change representation to tile-relative coordinates for segment endpoints.
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    raphlinus committed Nov 1, 2023
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  4. Test code for msaa

    @raphlinus
    raphlinus committed Nov 1, 2023
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  5. Antialiasing fixes 

    This commit fixes a number of problems with multisampled AA. There are three main changes:

* This fixes a cut'n'paste typo where the third word of four in resolution was computed incorrectly. This degraded antialiasing quality.

* There is a bit more logic in `is_bump` to handle crossings at the top of the tile better. This is not done in the even-odd variant because it is seemingly not needed. (I don't have a careful analysis why, but suspect it has something to do with the fact that double counting or getting the sign wrong is less critical in even-odd than nonzero).

* There is a tweak in tiling to cause vertical lines sent to fine to be not pixel-aligned. That's a difficult case for msaa (area doesn't care).

The latter two might be considered hacky, but examination of the test cases should improve confidence. There were artifacts in glyph rendering that this patch also improves, so in any case it's better than the previous state.
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    raphlinus committed Nov 1, 2023
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  6. Unbreak CI 

    CI is broken because the WebGPU stuff doesn't have stable semver guarantees. This pins the web-sys version to protect against that.
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    raphlinus committed Nov 1, 2023
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  7. Add comments to help explain msaa logic 

    To say that the msaa logic is dense and hard to understand is an understatement. I've added some comments which will I hope will help the reader navigate the code, but ultimately it requires a real explanation.

While reviewing the code, I realized that horizontal pixel-aligned lines are already being discarded by separate robustness logic, so that case doesn't need to be handled in is_bump, so I took it out.
    @raphlinus
    raphlinus committed Nov 1, 2023
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