From 359c5eb9e6c06413b8b8a11e8fcbbc457028fdde Mon Sep 17 00:00:00 2001 From: James Shaw Date: Wed, 28 Nov 2007 17:47:25 +0000 Subject: Fix alpha-blending maths (thanks to Michael Drake) svn path=/import/jshaw/libsprite/; revision=10001 --- trunk/example.c | 9 ++++++--- 1 file 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; -- cgit v1.2.3