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hb-view: Interpolate gradients premultiplied 

This is what the specs demand.
This commit is contained in:
Matthias Clasen 2022-12-23 00:54:05 -05:00 committed by Behdad Esfahbod
parent 21f78c8774
commit 13e0cb64f4
1 changed files with 24 additions and 0 deletions
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24
util/hb-cairo-utils.c
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@ -382,13 +382,37 @@ interpolate (float f0, float f1, float f)
return f0 + f * (f1 - f0); return f0 + f * (f1 - f0);
} }
static inline void
premultiply (color_t *c)
{
c->r *= c->a;
c->g *= c->a;
c->b *= c->a;
}
static inline void
unpremultiply (color_t *c)
{
if (c->a != 0.)
{
c->r /= c->a;
c->g /= c->a;
c->b /= c->a;
}
}
static void static void
interpolate_colors (color_t *c0, color_t *c1, float k, color_t *c) interpolate_colors (color_t *c0, color_t *c1, float k, color_t *c)
{ {
// According to the COLR specification, gradients
// should be interpolated in premultiplied form
premultiply (c0);
premultiply (c1);
c->r = c0->r + k * (c1->r - c0->r); c->r = c0->r + k * (c1->r - c0->r);
c->g = c0->g + k * (c1->g - c0->g); c->g = c0->g + k * (c1->g - c0->g);
c->b = c0->b + k * (c1->b - c0->b); c->b = c0->b + k * (c1->b - c0->b);
c->a = c0->a + k * (c1->a - c0->a); c->a = c0->a + k * (c1->a - c0->a);
unpremultiply (c);
} }
static inline float static inline float