GNU bug report logs - #21662
25.0.50; visible-bell causes display artifacts on OS X 10.11

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: David Caldwell <david <at> porkrind.org>
Subject: bug#21977: closed (Fixed)
Date: Mon, 23 Nov 2015 22:10:06 +0000

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Your bug report

#21662: 25.1; visible-bell corrupts screen on Mac OS X 10.11

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 21977 <at> debbugs.gnu.org.

-- 
21662: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=21662
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Anders Lindgren <andlind <at> gmail.com>
To: 21662-done <at> debbugs.gnu.org
Subject: Fixed
Date: Mon, 23 Nov 2015 23:09:39 +0100

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Fixed, see
http://git.savannah.gnu.org/cgit/emacs.git/commit/?h=emacs-25&id=345a9c8cd07111a8c8367e59404688544e8b8b1d
for details.

    -- Anders Lindgren

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From: David Caldwell <david <at> porkrind.org>
To: bug-gnu-emacs <at> gnu.org
Subject: 25.1; visible-bell corrupts screen on Mac OS X 10.11
Date: Sat, 21 Nov 2015 12:45:05 -0800

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Hello,

  Visible bell on Max OS X is a little weird in the first place: It
flashes a 128x128 rectangle in the middle of the OS
Window. Unfortunately, it's leaving artifacts and corrupted visuals
behind on Mac OS X 10.11. A nice example of the issue can be seen here:
https://cloud.githubusercontent.com/assets/617316/10954115/97430952-8319-11e5-81f4-25054836b901.png

It's easy to reproduce:

    M-x set-variable RET visible-bell RET t RET

...then hit `C-g`.

I've been looking into this and it actually appears to be a bug in Mac
OS X.

  I made an isolated test program from part of ns_ring_bell()
(https://github.com/caldwell/bracketed-window-op-test) that reproduces
the problem and have reported the bug to Apple (bug number 23642195, but
their bugs are private so having that doesn't help much).

  Since it's an OS X problem, I'm not really sure if I should be
reporting this here. But it seems to be confusing people, so maybe we
can work around it somehow until Apple fixes things. I tried to play
with NSCompositingOperation for a little bit last night but couldn't get
anything reasonable. I see in the git history that someone replaced
ns_ring_bell() with some CF graphics stuff, but it got reverted for some
reason (maybe GNUStep incompatibility?). Perhaps that can be resurrected
and reworked...

-David

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