bug#4759: 23.1; Minor Visual Corruption ("Flyspecks") on 23.1/OSX

[Tom Feist <t.feist@mhn-ltd.co.uk>]

When scrolling (either via wheel or cursor keys / C-n+p) under certain
conditions the buffer view will become corrupted with tiny 'flyspecks'  
which
appear to be parts of the buffer text which have been incorrectly over- 
drawn.
(That is, they typically share the same colours as the font-locked  
text which
"created" them moves across the screen.)

They remain in position fixed relative to the buffer (They do not move  
with the
text as it scrolls) until either a buffer switch or C-l redraws the  
screen.
They may also be eliminated if a portion of text scrolls over them and  
is
correctly over-drawn.

A sample of the corruption can be seen at
<url:http://metavore.org/faff/emacs-flyspecks.png> along the left-hand  
margin,
approx 7 chars in.

Finally, their occurrence frequency seems to be related to the  
specific face font. They
occur occasionally with the default (Apple-Monaco-13) font, but are  
far more
prevalent with the Anonymous_Pro font (available from
  <url:http://www.ms-studio.com/FontSales/anonymouspro.html>).

As yet I have not found a font which does not cause them, merely  
alters their
relative frequency of occurrence.

Further testing indicates that the problem may be related to anti- 
aliasing of the fonts.
Setting `ns-antialias-text' to nil eliminates the glitches, but at the  
cost of incredibly ugly
fonts, and so isn't really a suitable fix.

Thanks,

Tom Feist.

In GNU Emacs 23.1.1 (i386-apple-darwin9.8.0, NS apple-appkit-949.54)
  of 2009-08-16 on black.local
Windowing system distributor `Apple', version 10.3.949
configured using `configure  '--with-ns''

Important settings:
   value of $LC_ALL: nil
   value of $LC_COLLATE: nil
   value of $LC_CTYPE: nil
   value of $LC_MESSAGES: nil
   value of $LC_MONETARY: nil
   value of $LC_NUMERIC: nil
   value of $LC_TIME: nil
   value of $LANG: nil
   value of $XMODIFIERS: nil
   locale-coding-system: nil
   default-enable-multibyte-characters: t

Major mode: Emacs-Lisp

Minor modes in effect:
   shell-dirtrack-mode: t
   eldoc-mode: t
   cua-mode: t
   global-auto-complete-mode: t
   auto-complete-mode: t
   global-auto-revert-mode: t
   yas/global-mode: t
   yas/minor-mode: t
   diff-auto-refine-mode: t
   show-paren-mode: t
   tooltip-mode: t
   mouse-wheel-mode: t
   menu-bar-mode: t
   file-name-shadow-mode: t
   global-font-lock-mode: t
   font-lock-mode: t
   global-auto-composition-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t
   size-indication-mode: t
   column-number-mode: t
   line-number-mode: t
   transient-mark-mode: t

Recent input:
C-x C-f C-g M-x v e r s i o n <return> C-x C-f . e
m a c s <return> <wheel-down> <double-wheel-down> <triple-wheel-down>
<triple-wheel-down> <triple-wheel-down> <triple-wheel-down>
<triple-wheel-down> <triple-wheel-down> <triple-wheel-down>
<wheel-up> <double-wheel-up> <triple-wheel-up> <triple-wheel-up>
<triple-wheel-up> <triple-wheel-up> <wheel-down> M-x
e m a c s - b u g <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
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