All Manuals > CAPI User Guide > 13 Graphics Ports > 13.6 Combining source and target pixels


13.6.2 Combining pixels with :quality drawing

When the port's drawing-mode is :quality the graphics state parameter compositing-mode determines how the colors are combined, and operation is ignored.

compositing-mode :over means draw over the existing values, blending alpha values if they exist.

compositing-mode :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 .

Further compositing-mode values are supported on later versions of Cocoa and GTK+.

CAPI User Guide (Macintosh version) - 30 Aug 2011