Fix polygon feathering artifacts at sharp corners#7901
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segeljakt wants to merge 2 commits intoemilk:mainfrom
Open
Fix polygon feathering artifacts at sharp corners#7901segeljakt wants to merge 2 commits intoemilk:mainfrom
segeljakt wants to merge 2 commits intoemilk:mainfrom
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Preview available at https://egui-pr-preview.github.io/pr/7901-fixfeathering-sharp-corners View snapshot changes at kitdiff |
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Thanks for working on this! in #7554 @podusowski added some tests for this - could you add them to this PR too, so we can compare the fixes? |
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The miter join normal in `add_line_loop` has magnitude `1/cos(θ/2)`, which grows without bound at sharp corners, causing feathering vertices to be placed far outside the polygon. Clamp the miter factor to 2.0, which prevents artifacts while preserving correct feathering for corners wider than ~60°. Fixes emilk#7424
Visual test from @podusowski's emilk#7554 to allow comparing the two fix approaches.
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This looks pretty bad 😬 Looks like this PR, just like #7554, fixes the extrusions by nuking the feathering. I believe a proper fix that handles both requires adding another vertex to sharp corners |
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The miter join normal in
add_line_loophas magnitude1/cos(θ/2), which blows up at sharp corners. For a nearly-degenerate triangle this can push feathering vertices 100+ px outside the polygon, creating visible line artifacts.This clamps the miter factor to 2.0 (same idea as SVG's
stroke-miterlimit). Corners wider than ~60° are unaffected. Sharper corners get beveled feathering instead of mitered. This barely has a visual impact since the corners are sub-pixel.Snapshot diffs are just sub-pixel changes in menu bar tabs.
Tests
test_feathering_no_artifacts_on_sharp_triangleswith a few sharp polygon cases that fail without the fixFixes #7424
Example
Before the fix:
After the fix:
Disclosure
I used Claude Code to diagnose the error and come up with the fix. I hope this is ok.