When the port's
drawing-mode
is
:compatible
the graphics state parameter
operation
determines how the colors are combined, and
compositing-mode
is ignored
The allowed values of
operation
are the values of the Common Lisp constants
boole-1
,
boole-and
and so on. These are the allowed values of the first argument to the Common Lisp function
boole.
See the specification of
boole
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
:operation
boole-andc2
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