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authorJames Shaw <jshaw@netsurf-browser.org>2007-11-28 17:47:25 (GMT)
committer James Shaw <jshaw@netsurf-browser.org>2007-11-28 17:47:25 (GMT)
commit359c5eb9e6c06413b8b8a11e8fcbbc457028fdde (patch)
tree269eb7c69ad9bf2dff96110e2eb7a9b49132645d
parent2cdf0f9615f2c8c2f9c73619c967dd6cda5bba0f (diff)
downloadlibrosprite-359c5eb9e6c06413b8b8a11e8fcbbc457028fdde.tar.gz
librosprite-359c5eb9e6c06413b8b8a11e8fcbbc457028fdde.tar.bz2
Fix alpha-blending maths (thanks to Michael Drake)
svn path=/import/jshaw/libsprite/; revision=10001
-rw-r--r--trunk/example.c9
1 files changed, 6 insertions, 3 deletions
diff --git a/trunk/example.c b/trunk/example.c
index 7afd5a4..e2aa0e6 100644
--- a/trunk/example.c
+++ b/trunk/example.c
@@ -12,9 +12,12 @@ void sdl_draw_pixel(SDL_Surface* surface, uint32_t x, uint32_t y, uint32_t color
uint32_t bg_color = ((int) (x / 4.0) + ((int)(y / 4.0) % 2)) % 2 ? 0x99 : 0x66;
uint32_t alpha = color & 0x000000ff;
- uint32_t r = (bg_color + (((color & 0xff000000) >> 24) - bg_color) * (alpha / 255.0));
- uint32_t g = (bg_color + (((color & 0x00ff0000) >> 16) - bg_color) * (alpha / 255.0));
- uint32_t b = (bg_color + (((color & 0x0000ff00) >> 8) - bg_color) * (alpha / 255.0));
+ uint32_t r = (color & 0xff000000) >> 24;
+ uint32_t g = (color & 0x00ff0000) >> 16;
+ uint32_t b = (color & 0x0000ff00) >> 8;
+ r = ((alpha / 255.0) * r) + (((255-alpha) / 255.0) * bg_color);
+ g = ((alpha / 255.0) * g) + (((255-alpha) / 255.0) * bg_color);
+ b = ((alpha / 255.0) * b) + (((255-alpha) / 255.0) * bg_color);
uint32_t mapped_color = SDL_MapRGB(surface->format, r, g, b);
*pixel = mapped_color;