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Avoid calculation when over px is transparent

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This commit is contained in:
Kovid Goyal 2021-02-04 14:26:10 +05:30
parent 0f18fedf13
commit 2650c7dd9e
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GPG Key ID: 06BC317B515ACE7C
1 changed files with 7 additions and 5 deletions
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kitty/graphics.c
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@ -861,12 +861,14 @@ blend_on_opaque(uint8_t *under_px, const uint8_t *over_px) {
static inline void
alpha_blend(uint8_t *dest_px, const uint8_t *src_px) {
if (src_px[3]) {
const float dest_a = (float)dest_px[3] / 255.f, src_a = (float)src_px[3] / 255.f;
const float alpha = src_a + dest_a * (1.f - src_a);
dest_px[3] = (uint8_t)(255 * alpha);
if (!dest_px[3]) { dest_px[0] = 0; dest_px[1] = 0; dest_px[2] = 0; return; }
for (unsigned i = 0; i < 3; i++) dest_px[i] = (uint8_t)((src_px[i] * src_a + dest_px[i] * dest_a * (1.f - src_a))/alpha);
}
}
typedef struct {
bool needs_blending;