fix: anti-alias presentation downscaling with an area filter - #29
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Presentation scaling picked a single nearest source pixel per output pixel, so downscaling a 4K output to a window-sized presentation drops most source pixels and renders text with heavy aliasing. Average the source region each output pixel covers instead (integer box filter, rounded). For upscaling the box degenerates to one source pixel, matching the previous behavior, and the identity path is untouched. (cherry picked from commit 5edcda3)
maryny4
marked this pull request as draft
August 6, 2026 13:18
maryny4
marked this pull request as ready for review
August 6, 2026 13:22
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Problem
Presentation scaling picks a single nearest source pixel per output pixel. When a 4K physical output is presented at a window-sized resolution (e.g. 3840x2160 → ~1536x864), most source pixels are simply dropped, and fine content — text above all — renders with heavy aliasing ("pixelated" look reported by users of physical-output capture).
Fix
Average the source region each output pixel covers (integer box filter with rounding). Downscaling now anti-aliases; for upscaling the box degenerates to a single source pixel, matching the previous behavior byte for byte, and the identity path stays zero-copy as before.
A regression test downscales a black/white pair to one pixel and asserts mid-gray — nearest sampling would return one of the extremes.
cargo fmt --check,clippy -- -D warnings,cargo test(both feature sets) pass.