draw-line* limitations

• To: DCPL@fuji.ila.com
• Subject: draw-line* limitations
• From: "John G. Aspinall" <JGA@alderaan.scrc.symbolics.com>
• Date: Mon, 3 Jun 1991 10:43-0400
• Cc: clim@BBN.COM, Bug-CLIM@fuji.ila.com
• In-Reply-To: <19910603135124.4.DCPL@DIAMOND-HEAD.ILA.COM>

[customer removed in case there's some other problem]

    Date: Mon, 3 Jun 1991 09:51 EDT
    From: "David C. P. Linden" <DCPL@fuji.ila.com>
    To: kanderso@BBN.COM, rsl@ila.com, clim@BBN.COM, Bug-CLIM@fuji.ila.com
    cc: kanderson@BBN.COM
    In-Reply-To: <9105311948.AA00139@meillet.ila.com>,
		 <19910531201412.4.RSL@MAX-FLEISCHER.SF.Dialnet.ILA.COM>,
		 <19910531202840.5.RSL@MAX-FLEISCHER.SF.Dialnet.ILA.COM>,
		 The message of 31 May 91 17:41 EDT from kanderso@BBN.COM,
		 <19910531232301.2.RSL@MAX-FLEISCHER.SF.Dialnet.ILA.COM>

    This by-hand form of clipping is incorrect because it doesn't preserver
    slope.  Suppose the draw-line were
	    (draw-line* m 0 0 1e6 1e10)
    This is a nearly vertical line, but your naive clipping will turn it
    into a 45 degree diagonal line.  This is the real reason it's a pain in
    the neck.  I don't have any good solutions off the top of my head, other
    than to say that CLIM needs to be able to fall back on some graphics
    rendering code in Lisp in order to clip this correctly.  Exactly where
    and how that is to be done I can't address at this time.

I seem to have missed the referenced messages.  Could you forward them to me?
Clipping a line to a convex region (properly) is very simple.  Perhaps I could
supply some example code if I knew what the problem was.

0,,

• draw-line* limitations
• From: "David C. P. Linden" <DCPL@fuji.ila.com>

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