artist-draw-sline is a compiled Lisp function in `
(artist-draw-sline X1 Y1 X2 Y2)
Draw a straight line from X1, Y1 to X2, Y2.
Straight lines are vertical, horizontal or diagonal lines.
They are faster to draw and most often they are what you need
when drawing a simple image.
Output is a straight line, which is a list on the form
(END-POINT-1 END-POINT-2 SHAPE-INFO).
END-POINT-1 and END-POINT-2 are two-element vectors on the form [X Y].
SHAPE-INFO is a vector [START-X START-Y LENGTH-OF-LINE DIRECTION
ORIGINAL-CHAR-1 ORIGINAL-CHAR-2 ... ].