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Bug #7497: Change _cairo_color_compute_shorts to not rely on any particular floating-point epsilon value.

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Carl Worth 2006-08-30 14:43:21 -07:00
parent 71037f3612
commit b62710d4f8
1 changed files with 16 additions and 8 deletions
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24
src/cairo-color.c
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@ -89,19 +89,27 @@ _cairo_color_init_rgb (cairo_color_t *color,
_cairo_color_init_rgba (color, red, green, blue, 1.0);
}
/* We multiply colors by (0x10000 - epsilon), such that we get a uniform
* range even for 0xffff. In other words, (1.0 - epsilon) would convert
* to 0xffff, not 0xfffe.
/* Convert a double in [0.0, 1.0] to an integer in [0, 65535]
* The conversion is designed to divide the input range into 65536
* equally-sized regions. This is achieved by multiplying by 65536 and
* then special-casing the result of an input value of 1.0 so that it
* maps to 65535 instead of 65536.
*/
#define CAIRO_COLOR_ONE_MINUS_EPSILON (65536.0 - 1e-5)
static inline uint16_t _color_to_short (double d)
{
uint32_t i;
i = (uint32_t) (d * 65536);
i -= (i >> 16);
return i;
}
static void
_cairo_color_compute_shorts (cairo_color_t *color)
{
color->red_short = color->red * color->alpha * CAIRO_COLOR_ONE_MINUS_EPSILON;
color->green_short = color->green * color->alpha * CAIRO_COLOR_ONE_MINUS_EPSILON;
color->blue_short = color->blue * color->alpha * CAIRO_COLOR_ONE_MINUS_EPSILON;
color->alpha_short = color->alpha * CAIRO_COLOR_ONE_MINUS_EPSILON;
color->red_short = _color_to_short (color->red * color->alpha);
color->green_short = _color_to_short (color->green * color->alpha);
color->blue_short = _color_to_short (color->blue * color->alpha);
color->alpha_short = _color_to_short (color->alpha);
}
void