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Add cogl_color_premultiply()

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Add a convenience function to convert an ARGB color from
non-premultiplied to premultiplied form.

http://bugzilla.openedhand.com/show_bug.cgi?id=1406

Signed-off-by: Robert Bragg <robert@linux.intel.com>
This commit is contained in:
Owen W. Taylor 2009-05-09 14:39:01 -04:00 committed by Robert Bragg
parent fd9d87bc3a
commit dcc4f14169
2 changed files with 20 additions and 0 deletions
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12
cogl-color.h
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@ -228,6 +228,18 @@ float cogl_color_get_blue (const CoglColor *color);
*/
float cogl_color_get_alpha (const CoglColor *color);
/**
* cogl_color_premultiply:
* @color: the color to premultiply
*
* Converts a non-premultiplied color to a pre-multiplied color. For
* example, semi-transparent red is (1.0, 0, 0, 0.5) when non-premultiplied
* and (0.5, 0, 0, 0.5) when premultiplied.
*
* Since: 1.0
*/
void cogl_color_premultiply (CoglColor *color);
G_END_DECLS
#endif /* __COGL_COLOR_H__ */

8
common/cogl-color.c
View file

@ -153,6 +153,14 @@ cogl_color_get_alpha (const CoglColor *color)
return ((float) color->alpha / 255.0);
}
void
cogl_color_premultiply (CoglColor *color)
{
color->red = (color->red * color->alpha + 128) / 255;
color->green = (color->green * color->alpha + 128) / 255;
color->blue = (color->blue * color->alpha + 128) / 255;
}
void
cogl_set_source_color4ub (guint8 red,
guint8 green,