You can draw ellipses and polygons with the functions
You can specify whether a shape is drawn in outline or is filled (with the graphics state foreground color) by the argument filled .
For example, to clear a rectangular region of an output pane, do
(draw-rectangle pane x y width height
is needed only when the color has alpha, and
is needed only if it is different from the
's graphics state.
CAPI User Guide (Unix version) - 30 Aug 2011