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Use pre-multiplied colors by default

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wlr_scene_rects expect their color to be pre-multiplied
while cairo_set_source_rgba() expects them to not be
pre-multiplied. With this patch we now use premultiplied
colors internally by default and then reverse it when
setting cairo colors.

This ensures the titlebar uses a consistent color in case
it was defined with some transparency by the user.

Fixes: #1684
This commit is contained in:
Consolatis 2024-04-06 17:46:30 +02:00
parent 33859138cf
commit c35ba02ffa
3 changed files with 20 additions and 4 deletions
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14
src/common/graphic-helpers.c
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@ -85,7 +85,19 @@ draw_cairo_border(cairo_t *cairo, struct wlr_fbox fbox, double line_width)
void
set_cairo_color(cairo_t *cairo, const float *c)
{
cairo_set_source_rgba(cairo, c[0], c[1], c[2], c[3]);
/*
* We are dealing with pre-multiplied colors
* but cairo expects unmultiplied colors here
*/
float alpha = c[3];
if (alpha == 0.0f) {
cairo_set_source_rgba(cairo, 0, 0, 0, 0);
return;
}
cairo_set_source_rgba(cairo, c[0] / alpha, c[1] / alpha,
c[2] / alpha, alpha);
}
struct surface_context