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Fixed handling of the alpha channel in the downscaler.

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This commit is contained in:
Guillaume Melquiond 2010-12-19 20:01:01 +00:00
parent 596b9585eb
commit 04d8217e71
1 changed files with 12 additions and 11 deletions
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23
src/sdl_utils.cpp
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@ -516,7 +516,7 @@ surface scale_surface_blended(const surface &surf, int w, int h, bool optimize)
double xsrc = 0.0;
for(int xdst = 0; xdst != w; ++xdst, xsrc += xratio) {
double red = 0.0, green = 0.0, blue = 0.0, alpha = 0.0;
double summation = 0.0;
double summation = 0.0, a_summation = 0.0;
// We now have a rectangle, (xsrc,ysrc,xratio,yratio)
// which we want to derive the pixel from
@ -531,23 +531,24 @@ surface scale_surface_blended(const surface &surf, int w, int h, bool optimize)
Uint8 r,g,b,a;
SDL_GetRGBA(src_pixels[yloc * src->w + xloc], src->format, &r, &g, &b, &a);
const double value = xsize*ysize*double(a)/255.0;
double value = xsize * ysize;
a_summation += value;
alpha += a * value;
value *= a / 255.0;
summation += value;
red += r*value;
green += g*value;
blue += b*value;
alpha += a*value;
}
}
if(summation == 0.0)
summation = 1.0;
red /= summation;
green /= summation;
blue /= summation;
alpha /= summation;
if (summation != 0.0) {
alpha /= a_summation;
summation = 1/summation;
red *= summation;
green *= summation;
blue *= summation;
}
dst_pixels[ydst*dst->w + xdst] = SDL_MapRGBA(dst->format,Uint8(red),Uint8(green),Uint8(blue),Uint8(alpha));
}