Graphics Ports allow users to write source-compatible applications for different host window systems. Graphics Ports are the destinations for drawing primitives. They are implemented with a generic host-independent part and a small host-specific part.
Graphics Ports implement a set of drawing functions and a mechanism for specifying the graphics state to be used in each drawing function call. There are two types of Graphics Port: on-screen ports and off-screen ports. On-screen graphics ports correspond to visible windows, while off-screen graphics ports can be used for building up graphical images for subsequent copying to the screen.
See the LispWorks CAPI Reference Manual for full reference entries on all the Graphics Ports functions, macros, classes and types.