Alpha-Blending

Does that function work? It looks to me like it won''t work...
And that''s for one set of pixels only eh? So if you were to write an alpha blitter you should put that right into the code of the blitter. DON''T call a sub function (Especially that simple of one) 100''s of times when cycling through an image..

So a couple Q''s. Using 16bpp? It looks it ''cause your using words. But you could just be a sloppy programming putting bytes into those params in 8bpp!

If so you need to take into account a few things, to start you gotta take into account wheather it''s 555 or 565 mode.
Then you mask off the lower bit of *each* color, before adding.
So here''s some rough pseudo/real code

if (Is_555 == TRUE)    //We''re using 555 mode
{
color1 &= 0x7BDE;    //Mask off lower bit of each color
color2 &= 0x7BDE;    //Mask off lower bit of each color
}
else    /We''re using 565 mode
{
color1 &= 0xF7DE;    //Mask off lower bit of each color
color2 &= 0xF7DE;    //Mask off lower bit of each color
}
color1 = color1 >> 1;    // Shift right 1 (Essentially divide each color value by half)
color2 += color2 >> 1;    // Shift right 1 and add last color(Essentially divide each color value by half)
return color1;    // Return our mixed colors

That looks a bit more like it...
- Ben

Yes it is 16bpp. And 555 format. It''s only in a function just to test that it works. Not for general use.

The original code was this :

color1 := color1 shr 1;
color2 := color2 shr 1;
color1 := (color1 and $3DEF) - $7BEF;
color2 := (color2 and $3DEF) - $7BEF;
result := color1 + color2;

I just removed the unnecessary commands. Sorry I didn''t make myself clear. I will do a separate one for 565 format later ... but for now, I''m doing this one

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