Path: utzoo!mnetor!uunet!mcvax!unido!ecrcvax!johng
From: johng@ecrcvax.UUCP (John Gregor)
Newsgroups: comp.graphics
Subject: Re: thick lines, circles and ellipses
Message-ID: <471@ecrcvax.UUCP>
Date: 17 Jan 88 13:27:36 GMT
References: <694@prefix.liu.se> <16183@watmath.waterloo.edu> <696@portofix.liu.se>
Reply-To: johng@ecrcvax.UUCP (John Gregor)
Organization: ECRC, Munich 81, West Germany
Lines: 30
Keywords: computer graphics, circles, ellipses, algorithms

In article <696@portofix.liu.se> kjepo@portofix.liu.se (Kjell Post) writes:
>Why not use a thicker pencil?
>
>What I'm saying is that you can print a larger dot instead of just a pixel.
>This is the method used by ditroff where they draw lines, arcs and b-splines
>with the '.' character. By altering the fontsize you get different line widths.

That may be fine for output to a laser printer, but it is extremely inefficient
for any sort of interactive graphics.  Here is an example:

Assume your big dot is:          ##
				####
Also assuming square pixels     ####
				 ##

Then drawing a line (slope == 1) would look like:

	     11
            2211
           23221
	  23232       The numbers correspond to the number of times the 
	 12232        pixel is written.
	 1122
	  11

Even though there is a fix for lines, this scheme is completely impractical
for curves.  I recommend scan converting the polygon.

				John Gregor
                      johng%ecrcvax.UUCP@germany.CSNET