bug#10895: Quirky behaviours with Arabic text

[sergei karhof <karhof21@gmail.com>]

I want to report some quirky behaviours of Emacs (devel 24.0.93 version,
running under Windows 7), when dealing with Arabic text:

1) in some fonts (e.g. courier New), the vowel marks (harakaat) are
not displayed, despite the fact that the texts contains them. However,
if the cursor passes over the relevant text, moving in the
right-to-left direction, the vowel marks become visible. Curiously, if
the cursor passes back on the text, moving in the left-to-right
direction, the vowel marks disappear.
This problem manifests itself in different ways according to the font used.
With other fonts, the problem is only partial: only part of the
diacritic signs is visible, and by passing over them with the cursor
(from right to left), they become fully visible. When passing over the
text in the opposite direction, they again become half-visible.

2) the rendering of the vowel marks is poor even when they are
displayed. For instance, vowel marks partially overlap some of the
letters, e.g. the kasrah sign overlaps the two dots of the letter yaa.

3) vowel marks are not always in synch with the main text, so that
they sometimes appear in a displaced position (e.g. on the previous
letter). This is totally unacceptable, of course.

Bottomline: there are multiple problems with the visual rendering of
the diacritics.