Round join tessellation and CPU edge accuracy - #417
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…PU edge accuracy - CalcArc and stroke_calc_arc take their vertex count from the guarded GetArcSubdivisionCount and stroke_arc_subdivision_count used by round caps. - StrokeOptions.ArcDetailScale rejects values not greater than zero. - DefaultRasterizer: band boundary X is interpolated from the segment endpoint and rounded to nearest, coverage uses the exact doubled area, and the DDA walkers round row and column boundaries to nearest. - Tests: ArcDetailScale validation, subdivision count monotonicity, and CPU/GPU parity theories for round joins at scales 0.01 to 16. - Reference images updated for the corrected edge coverage.
Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## release/3.1.x #417 +/- ##
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Coverage 79% 79%
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Files 232 232
Lines 27356 27359 +3
Branches 3113 3114 +1
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+ Hits 21875 21879 +4
+ Misses 4589 4587 -2
- Partials 892 893 +1
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Prerequisites
Description
Round joins in both backends computed their arc step with an unguarded expression, while round caps used a guarded one. A zero or negative
ArcDetailScaleturned round joins into bevels on the CPU and gave the GPU an undefined vertex count. Joins now share the cap helper, andStrokeOptions.ArcDetailScalerejects values that are not greater than zero.Parity tests at non-default scales exposed three CPU rasterizer errors on antialiased edges. Band boundary X accumulated truncation across 16 row bands, so long slanted edges drifted by up to a few hundredths of a pixel. Coverage was quantized to 1/256 steps before the blend. The DDA walkers floored every row and column boundary. All three are fixed, and CPU and GPU output now agree to the precision of the CPU's 24.8 fixed point geometry.
Reference images are updated for the corrected edge coverage.