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From: mouse@shamash.mcrcim.mcgill.EDU (der Mouse)
Newsgroups: comp.windows.x
Subject: Re: X11R4 pixelization rules
Message-ID: <9006270552.AA01985@shamash.McRCIM.McGill.EDU>
Date: 27 Jun 90 05:52:41 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 32

>> My point is that "the center of the pixel" is not a precisely
>> specified notion.
> The protocol description seems to implicitly define that pixel
> centres are on integral coordinates (I have a feeling there is an
> explicit statement somewhere, but I cannot find it).

rws posted something saying it's in the Glossary.  As I noted in a
followup, I have an incomplete copy of the protocol document; my copy
has no glossary.  (Soon to be remedied, I hope.)

>> Since line endpoints are always on integer coordinates, the most
>> reasonable jaggies happen if pixel centres have coordinates of the
>  ^^^^^^^^^^^^^^^^^^
>> form (integer+.5,integer+.5), but [...].

> Why do you say this?

Because I hadn't thought about it enough.  What I meant to refer to was
the differences among

O.............  OOOOOOO.......  OOOOOOOOOOOOO.
.OOOOOOOOOOOOO  .......OOOOOOO  .............O

for a line drawn between the upper left and lower right corners of a
2x14 rectangle.  As the pixel grid is shifted with respect to the
coordinate grid, each of the above pixelizations (and several others)
is possible.

					der Mouse

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