bug#11390: 24.1.50; Emacs on OSX -- strange artifacts in the buffer

[Eugene Dedits]

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Please write in English if possible, as the Emacs maintainers
usually do not have translators for other languages.

Please describe exactly what actions triggered the bug, and
the precise symptoms of the bug.  If you can, give a recipe
starting from `emacs -Q':



If Emacs crashed, and you have the Emacs process in the gdb debugger,
please include the output from the following gdb commands:
    `bt full' and `xbacktrace'.
For information about debugging Emacs, please read the file
/Applications/Emacs.app/Contents/Resources/etc/DEBUG.


In GNU Emacs 24.1.50.2 (x86_64-apple-darwin10.8.0, NS apple-appkit-1038.36)
of 2012-05-01 on pde
Windowing system distributor `Apple', version 10.3.1038
Configured using:
`configure '--with-ns' '--prefix=/Users/eugene/tmp/emacs/build''

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Attached screenshot shows strange artifacts that appear *some times* when I
-- scroll buffer with the mouse wheel
-- switch to some other application and back


These artifacts disappear if I
-- select region
-- increase\decrease font size
-- move cursor over those positions


This seems to be independent of the major mode.


If I use smaller font size (Monaco 10pt, no antialiasing) this never happens. 
For any bigger
font size (Monaco 12pt and up, antialiased) these artifacts show up.


I was able to reproduce it using
-- my own build of emacs 24.1.50
-- latest pre-builds found on EmacsForOSX
-- latest Aquamacs
------------------------------------------------------------------------------------------


Thanks,
Eugene.



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