When the port's
the graphics state parameter
determines how the colors are combined, and
The allowed values of
are the values of the Common Lisp constants
and so on. These are the allowed values of the first argument to the Common Lisp function
See the specification of
in the ANSI Common Lisp standard for the full list of operations.
The color combination corresponds to the logical operation defined there, as if by calling
(boole operation new-pixel screen-pixel )
For example, passing
provides a graphics state where graphics ports drawing functions draw with the bitwise AND of the foreground color and the complement of the existing color of each pixel.
Note: Graphics State operation is not supported by Cocoa/Core Graphics so this parameter is ignored on Cocoa.
CAPI User Guide (Unix version) - 30 Aug 2011