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Re: Bidi reordering engine upgraded

From: grischka
Subject: Re: Bidi reordering engine upgraded
Date: Fri, 17 Oct 2014 13:12:58 +0200
User-agent: Thunderbird (Windows/20090812)

But there are W+1 pixels in a line that starts at X and ends at X+W.
W+1, not W.

 | 1         2         3
 | 012345678901234567890123456789
 |           ***********
 |                     ^ out out damned dot!

Count the stars, and you will see there are 11 of them, not 10.  Where
did the 11th one come from, when we requested a width of 10?

In general, drawing an horizontal or vertical line of length 10
needs 11 pixels to be set.

This is because to the human eye pixels are similar to points in math
(i.e.has location, does not have extent).  Therefor, a mental "magnifying
glass" (in order to be useful) needs to preserve the point-like property
of pixels unaffected from the "zoom factor".

Which means that what counts for line length is not number of pixels
but the spaces between.  See line of length 10, magnified:

    0   1   2   3   4   5   6   7   8   9   0
    *   *   *   *   *   *   *   *   *   *   *

(Disclaimer:  The above is not meant to necessarily support
conclusions about the behavior of XDrawRectangle or FrameRect,
or specific details thereof. :P)

--- grischka

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