12.5 Graphics state operation

The value in the operation slot of the graphics state determines how the foreground color is combined with the existing color for each pixel that is drawn.

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 slot is ignored on Cocoa.

LispWorks CAPI User Guide (Unix version) - 14 Jun 2006