This section describes how new drawings are combined with the existing pixel values in the target of the drawing to generate the result, according to graphics state parameters compositing-mode or operation.
Note: The full set of graphics state parameters is described under graphics-state.
The allowed values of
are the values of the Common Lisp constants
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.
(boole operation new-pixel screen-pixel )
For example, passing
boole-andc2 provides a graphics-state where graphics ports drawing functions draw with the bitwise AND of the
color and the complement of the existing color of each pixel.
:copy means that the source is written to the destination ignoring the existing values. If the source has alpha and the target does not, that has the effect of converting semi-transparent source to solid.
:copy is especially useful for creating transparent and semi-transparent pixmap ports, which can be displayed directly or converted to images by make-image-from-port.
CAPI User Guide and Reference Manual (Unix version) - 25 Feb 2015