Re: simple graphics question

[miller@SOL.CS.ROCHESTER.EDU (Brad Miller)]

    Date: Tue, 18 Dec 90 13:28 EST
    From: bill@CASSIOPEIA.Mystech.DialNet.Symbolics.com (Bill Anderson)

    hi,

    is there a simple (ie built-in) way to obtain a list of indices (points) of a 2d-array that
    would be "touched" if a line was drawn?

    example:

    2d-array bob  100x100

    if we "draw" from 20,20 to 27,32 i would like a list of "touched" indices 
    like (20 20 21 23 ...) returned

    basically the equivalent to graphics:compute-cubic-spline-points but for a simple line

    -thanks

I think you want GRAPHICS:DRAW-LINE-DRIVER. Here's a short example: (CONS-TU
needs to do something with every point the line will pass through, but not
necessarily the endpoints - for your purposes, it's called on each pixel)

(GRAPHICS:DRAW-LINE-DRIVER (X (END1 SEG)) (Y (END1 SEG)) (X (END2 SEG)) (Y (END2 SEG)) NIL
			   #'(LAMBDA (WIDTH HEIGHT X Y)
			       (COND
				 ((AND (EQL WIDTH 1) (EQL HEIGHT 1))
				  (CONS-TU X Y))
				 ((EQL WIDTH 1)
				  (DOTIMES (N HEIGHT)
				    (CONS-TU X (+ N Y))))
				 ((EQL HEIGHT 1)
				  (DOTIMES (N WIDTH)
				    (CONS-TU (+ N X) Y))))))

Hope this helps,
----
 Brad Miller		U. Rochester Comp Sci Dept.
 miller@cs.rochester.edu {...allegra!rochester!miller}