CIGAL Reference Manual, Chapter 2 (Commands): ELLIPSE
usage: ellipse [ color vc vpX vpY width flag ]
or ellipse [ color vc radX radY width flag ]
or ellipse [ color cx cy radX radY width flag ]
ELLIPSE draws an ellipse on the graphics display by adding line drawing instructions to the list of graphics vectors. The ellipse is drawn with intensity variable COLOR (default COLOR is the value of the internal variable LCOLOR).
Determine the position of the ellipse by the coordinates of the center and the size of the ellipse. The size is established either by specifying a point on the perimeter or by specifying the radii along the X and Y axes. The center coordinates can either be a 3-D vector or a set of explicit X and Y values (in which case Z is set to the current value of the internal variable ZVALUE: see ZVALUE(4)). If the center or radii are not specified then ELLIPSE waits for cursor input to specify the missing information.
The WIDTH parameter specifies the width of the lines to be drawn and can take on values 1 to 15. The FLAG parameter allows you to select various drawing options (these can be combined by addition):
1 - draw shape in absolute coordinates (ignoring transformation and clipping settings). 2 - don't store vectors in VECS (assumed if FLAG & 1). 4 - store lines as individual vectors to facilitate transformations (ignored if FLAG & 3). 8 - paint inside of ellipse. 16 - XOR values rather than replacing them.
FLAG's default value varies according to the context. If ELLIPSE is not called during a SKETCH command then the default FLAG is set at 2. If the coordinate system has been transformed by rotating around either the X or Y axes then FLAG has 4 set by default (see ROTATE(2), GFLAGS(4)).
BOX(2), CIRCLE(2), GFLAGS(4), GRAPHICS(1), LCOLOR(4), LINE(2), LWIDTH(4), ROTATE(2), ZVALUE(4)