PRINT_GRAPHICS@ takes one argument which is a user-defined callback function.
It calls OPEN_PRINTER@ in order to display the standard open printer dialog, then it calls the callback function and then
CLOSE_PRINTER@. For example, PRINT_GRAPHICS@ can be used together with a callback function that uses %pl - SIMPLEPLOT Graphics Region[external] in order
to print a graph. When the callback draws directly to the graphics object (using routines such as DRAW_LINE_BETWEEN@), a
call to AUTO_SCALE_FONT@() will automatically scale the font to a reasonable size for the printer resolution. Otherwise
CLEARWIN_INFO@ (with "GRAPHICS_WIDTH" and "GRAPHICS_DEPTH") can be called in order to get the pixel width and height and
to assign a suitable scaling factor in a call to SCALE_FONT@.
PRINT_GRAPHICS@ automatically sets the default line width (see SET_LINE_WIDTH@) to a value that is reasonable for the
printer resolution. It returns zero if CANCEL is selected from the open printer dialog. Otherwise it returns the value
returned by the callback function.