Contents  Introduction  Basic Blending  Get it Working  Tried them all!  Who needs MMX?  Who needs  MMX? (cont)  MMX Version  Conclusion  Printable version

FIRST ATTEMPT: Just get it working

The basic idea for alpha blending a non-indexed color mode (16bpp, 24bpp, etc) pixel is to breakdown both the source and destination pixel into their red, green, and blue color components or channels. Perform the above alpha blending equation on each channel then recombine the channels to form the resulting alpha blended pixel. Listing 1 shows some sample code that puts all of this together.

The code above is designed for a 16bpp surface with a format of 5-6-5. It also checks to see if the srcPixel is equal to the ColorKey in which case it skips drawing this pixel. This gives us transparency as well as alpha blending. This is your basic alpha blending function. We will use the performance of this function as our baseline and will compare subsequent attempts against the numbers below to see how much improvement we have achieved.

Performance of the First Attempt:

Milliseconds / function call	= 11.54
Cycles per pixel	= 53

Next : Tried Them All!