Help with how to add RGBA values

[spiffen]

Hi.

I'm currently working on a game where I do some simple pixel modifications when loading graphics. What I tried to do was to build a function that could take two RGBA values and add them, but I'm having real trouble with the alpha values. I know how to do it when using only RGB colors but when including alpha everything gets much trickier. Since I use Paint.NET when creating graphics and I know it can blend these colors very well, I'm hoping any developer or pixel color expert can help me how to write a function like this:

u32 blendPixel(u32 baseColor, u32 paintColor) {
   u8 baseRed = getRed(baseColor);
   u8 baseGreen = getGreen(baseColor);
   u8 baseBlue = getBlue(baseColor);
   u8 baseAlpha = getAlpha(baseColor);

   u8 paintRed = getRed(paintColor);
   u8 paintGreen = getGreen(paintColor);
   u8 paintBlue = getBlue(paintColor);
   u8 paintAlpha = getAlpha(paintColor);

   u8 newRed = ???
   u8 newGreen = ???
   u8 newBlue = ???
   u8 newAlpha = ???

   return makecol(newRed, newGreen, newBlue, newAlpha);
}

[Simon Brown]

This isn't a programming forum - I suggest posting in the CodeProject or MSDN forums instead.