Pixels to be painted on a device make a reference to three separate places: the destination, the source and a texture. These pixels are combined to create the actual pixel to be placed into the destination.
Such a combination is defined by a bitwise logical operation, called the paint operation. In Allegro CL, there are 256 possible paint operations that are given numbers from 0 to 255. There are eight possible minterms (of the three places): dst, ds~t, d~st,~dst, d~s~t,~ds~t,~d~st,and ~d~s~t where d is destination, s is source and t is texture (and ~ is the logical not operation). Each minterm may be present or absent from a paint operation.
A source pixel is copied to the corresponding destination pixel whenever the minterm representing the state of that pixel in the source, destination and texture pixmaps is present in the paint operation. (The minterm is "present" if its bit is on in the paint argument.) Thus there are 256 possible operations. Minterms are given the following weights (and to aid programming, named constants set to them):
dst 128 ds~t 64 d~st 32 ~dst 8 d~s~t 16 ~ds~t 4 ~d~st 2 ~d~s~t 1
Common Graphics and IDE documentation is described in About Common Graphics and IDE documentation in cgide.htm.
The documentation is described in introduction.htm and the index is in index.htm.
Copyright (c) 1998-2000, Franz Inc. Berkeley, CA., USA. All rights reserved.
Created 2000.10.5.