Exemple #1
0
NS_ComposeColors(nscolor aBG, nscolor aFG)
{
  // This function uses colors that are non premultiplied alpha.
  PRIntn r, g, b, a;

  PRIntn bgAlpha = NS_GET_A(aBG);
  PRIntn fgAlpha = NS_GET_A(aFG);

  // Compute the final alpha of the blended color
  // a = fgAlpha + bgAlpha*(255 - fgAlpha)/255;
  FAST_DIVIDE_BY_255(a, bgAlpha*(255-fgAlpha));
  a = fgAlpha + a;
  PRIntn blendAlpha;
  if (a == 0) {
    // In this case the blended color is totally trasparent,
    // we preserve the color information of the foreground color.
    blendAlpha = 255;
  } else {
    blendAlpha = (fgAlpha*255)/a;
  }
  MOZ_BLEND(r, NS_GET_R(aBG), NS_GET_R(aFG), blendAlpha);
  MOZ_BLEND(g, NS_GET_G(aBG), NS_GET_G(aFG), blendAlpha);
  MOZ_BLEND(b, NS_GET_B(aBG), NS_GET_B(aFG), blendAlpha);

  return NS_RGBA(r, g, b, a);
}
Exemple #2
0
NS_ComposeColors(nscolor aBG, nscolor aFG)
{
  PRIntn bgAlpha = NS_GET_A(aBG);
  PRIntn r, g, b, a;

  // First compute what we get drawing aBG onto RGBA(0,0,0,0)
  MOZ_BLEND(r, 0, NS_GET_R(aBG), bgAlpha);
  MOZ_BLEND(g, 0, NS_GET_G(aBG), bgAlpha);
  MOZ_BLEND(b, 0, NS_GET_B(aBG), bgAlpha);
  a = bgAlpha;

  // Now draw aFG on top of that
  PRIntn fgAlpha = NS_GET_A(aFG);
  MOZ_BLEND(r, r, NS_GET_R(aFG), fgAlpha);
  MOZ_BLEND(g, g, NS_GET_G(aFG), fgAlpha);
  MOZ_BLEND(b, b, NS_GET_B(aFG), fgAlpha);
  MOZ_BLEND(a, a, 255, fgAlpha);
  
  return NS_RGBA(r, g, b, a);
}