Path: utzoo!attcan!uunet!lll-winken!ames!apple!bloom-beacon!EXPO.LCS.MIT.EDU!rws
From: rws@EXPO.LCS.MIT.EDU
Newsgroups: comp.windows.x
Subject: Re: X Windows fill rule
Message-ID: <8906022035.AA02929@expire.lcs.mit.edu>
Date: 2 Jun 89 20:35:10 GMT
References: <8906022002.AA21798@amd-26.hac.com>
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 37


    Why does X Windows use this fill rule?

I'm too tired to repeat the arguments.  Maybe you can find someone with old
xpert archives.  A primary argument is that, whatever the definition is,
primitives laid end-to-end should never cause a pixel to be touched more than
once, and should cause no gaps.  I don't know if your definition
satsifies that or not.

    When you specify a rectangle to be filled isn't it reasonable to expect
    that the entire rectangle will be filled?

Yes, and X does.  The problem is simply that we have different notions of
what it means to specify a rectangle.  X specifies a width and height for a
rectangle.  The area drawn consists of that many pixels across and that many
pixels high.  Yours sounds like width+1 and height+1.  Whether that's what
you would "expect" probably depends on which school you went to. :-)

    2)  Is it critical that I somehow force our hardware to use a more
    primitive fill algorithm?

I don't know what metric you're using to define "primitive".

    Does anyone see a problem with just
    using the fill algorithm we have implemented in hardware?

Well, it doesn't conform to the protocol definition.

    Why does X specify a fill rule anyway?

So that applications can depend on consistent graphics across platforms.

    There are different 
    circle and line algorithms yet X does not specify which one of
    these to use.

Yes, it does, look again.  There is a definition for arcs, and for wide lines.