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Better alpha mixing, should produce correct results

This commit is contained in:
LemonBoy 2014-08-08 13:33:24 +02:00
parent 8475ff4fdb
commit dbbdf373a3
1 changed files with 21 additions and 9 deletions
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30
bar.c
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@ -157,18 +157,30 @@ parse_color (const char *str, char **end, const uint32_t def)
if (str[0] == '#') {
errno = 0;
uint32_t tmp = strtoul(str + 1, end, 16);
/* Some error checking is definitely good */
if (errno)
tmp = def;
/* Xorg uses colors with premultiplied alpha.
* Don't do anything if we didn't acquire a rgba visual. */
if (visual != scr->root_visual) {
const uint8_t a = ((tmp>>24)&255);
const uint32_t t1 = (tmp&0xff00ff) * (0x100-a);
const uint32_t t2 = (tmp&0x00ff00) * (0x100-a);
tmp = (a<<24)|(t1&0xff00ff)|(t2&0x00ff00);
}
return tmp;
/* Xorg uses colors with premultiplied alpha */
unsigned int a = (tmp&0xff000000) >> 24;
unsigned int r = (tmp&0x00ff0000) >> 16;
unsigned int g = (tmp&0x0000ff00) >> 8;
unsigned int b = (tmp&0x000000ff);
if (a) {
r = (r * 255) / a;
g = (g * 255) / a;
b = (b * 255) / a;
/* Clamp on overflow */
if (r > 255) r = 255;
if (g > 255) g = 255;
if (b > 255) b = 255;
} else
r = g = b = 0;
return a << 24 | r << 16 | g << 8 | b;
}
/* Actual color name, resolve it */