A_REPLACE | Replace the destination region with the source bitmap |
A_REVERSE | Replace the destination region with the inverse of the source bitmap |
A_NORMAL | OR the source bitmap into the destination region |
A_XOR | Exculsive-OR the source bitmap into the destination region |
A_OR | OR the source bitmap into the destination region |
A_AND | AND the source bitmap into the destination region |
A_SHADED | Mask the source bitmap so that every other pixel is turned off and replace
the destination region with that result (the source region is left unchanged) |