slint-sc: blend translucent rectangles - #12810
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The Color channel accessors were the only ones missing a doc comment.
A rectangle background with an alpha channel below 0xff now composites over what the frame buffer holds instead of overwriting it. Color gains a public composite_over implementing the Porter-Duff over operation. The window background must be a color literal with an alpha channel of 0xff, so that a rendered frame doesn't depend on what the buffer held beforehand. The check runs after inlining, so it sees a background inherited from a base component, and before ensure_window, which would otherwise give a non-Window root a synthetic background from the style.
tronical
marked this pull request as draft
August 6, 2026 15:40
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A
Rectanglebackground with an alpha channel below0xffnow composites overwhat the frame buffer already holds, instead of overwriting it.
Colorgains apublic
composite_over, the Porter-Duff over operation.The
Windowbackground must now be an opaque colour literal, so a renderedframe doesn't depend on what the buffer held before. It can no longer be set by
the application at all — a property reference can't be proven opaque.
Rectangles keep that freedom.