bug#41187: 28.0.50; Flipped text

bug#41187: 28.0.50; Flipped text

[Wasim Abbas]

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Hi folks,

I am seeing this issue on emacs head. The text randomly flips vertically. Very hard to reproduce. But if you open a very long C/C++ file like https://github.com/KhronosGroup/Vulkan-Headers/blob/master/include/vulkan/vulkan_core.h <https://github.com/KhronosGroup/Vulkan-Headers/blob/master/include/vulkan/vulkan_core.h> and keep moving around the buffer, cut 100ish lines and paste in another location and then move around again. You might hit the issue.

Here is a screenshot of it. I haven’t tried with emacs -Q yet but happy to try if required. 



//Wasim



In GNU Emacs 28.0.50 (build 1, x86_64-apple-darwin19.4.0, NS appkit-1894.40 Version 10.15.4 (Build 19E287))
of 2020-05-06 built on Wasims-iMac-Pro.local
Repository revision: 86fef6ab89ee54c6f78bc2064e55c5439e929827
Repository branch: master
Windowing system distributor 'Apple', version 10.3.1894
System Description:  Mac OS X 10.15.4

Recent messages:
Source file ‘/Users/wasimabbas/.emacs.d/init.el’ newer than byte-compiled file; using older file
Turn on helm-projectile key bindings
[yas] Prepared just-in-time loading of snippets successfully. [2 times]
You appear to be setting environment variables ("PATH") in your .bashrc or .zshrc: those files are only read by interactive shells, so you should instead set environment variables in startup files like .profile, .bash_profile or .zshenv.  Refer to your shell’s man page for more info.  Customize ‘exec-path-from-shell-arguments’ to remove "-i" when done, or disable ‘exec-path-from-shell-check-startup-files’ to disable this message.
Warning: /Users/wasimabbas/.emacs.d/init.el is newer than /Users/wasimabbas/.emacs.d/init.elc
For information about GNU Emacs and the GNU system, type C-h C-a.

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bug#41187: 28.0.50; Flipped text

[Eli Zaretskii]

> From: Wasim Abbas <abbas.wasim@gmail.com>
> Date: Mon, 11 May 2020 13:00:57 +0100
> 
> I am seeing this issue on emacs head. The text randomly flips vertically. Very hard to reproduce. But if you open a very long C/C++ file like https://github.com/KhronosGroup/Vulkan-Headers/blob/master/include/vulkan/vulkan_core.h <https://github.com/KhronosGroup/Vulkan-Headers/blob/master/include/vulkan/vulkan_core.h> and keep moving around the buffer, cut 100ish lines and paste in another location and then move around again. You might hit the issue.
> 
> Here is a screenshot of it. I haven’t tried with emacs -Q yet but happy to try if required. 

Wow!  That's got to be some weird problem with you video driver or the
display hardware.  Emacs never does anything like that.

bug#41187: 28.0.50; Flipped text

[Wasim Abbas]

> On 11 May 2020, at 16:23, Eli Zaretskii <eliz@gnu.org> wrote:
> 
>> From: Wasim Abbas <abbas.wasim@gmail.com>
>> Date: Mon, 11 May 2020 13:00:57 +0100
>> 
>> I am seeing this issue on emacs head. The text randomly flips vertically. Very hard to reproduce. But if you open a very long C/C++ file like https://github.com/KhronosGroup/Vulkan-Headers/blob/master/include/vulkan/vulkan_core.h <https://github.com/KhronosGroup/Vulkan-Headers/blob/master/include/vulkan/vulkan_core.h> and keep moving around the buffer, cut 100ish lines and paste in another location and then move around again. You might hit the issue.
>> 
>> Here is a screenshot of it. I haven’t tried with emacs -Q yet but happy to try if required. 
> 
> Wow!  That's got to be some weird problem with you video driver or the
> display hardware.  Emacs never does anything like that.

It could be. It's definitely isolated to emacs 28 and only to main emacs buffers. If you see the minibuffer and mode line it looks correct in the screenshot. Also if I do m-x the helm buffer appearing also gets flipped.
I was wondering if this is some option that is sent to core graphics while rendering the buffer that flips it? Any ideas how to debug this? Happy to give it a go.

bug#41187: 28.0.50; Flipped text

[Alan Third]

On Mon, May 11, 2020 at 06:23:24PM +0300, Eli Zaretskii wrote:
> > From: Wasim Abbas <abbas.wasim@gmail.com>
> > Date: Mon, 11 May 2020 13:00:57 +0100
> > 
> > I am seeing this issue on emacs head. The text randomly flips vertically. Very hard to reproduce. But if you open a very long C/C++ file like https://github.com/KhronosGroup/Vulkan-Headers/blob/master/include/vulkan/vulkan_core.h <https://github.com/KhronosGroup/Vulkan-Headers/blob/master/include/vulkan/vulkan_core.h> and keep moving around the buffer, cut 100ish lines and paste in another location and then move around again. You might hit the issue.
> > 
> > Here is a screenshot of it. I haven’t tried with emacs -Q yet but happy to try if required. 
> 
> Wow!  That's got to be some weird problem with you video driver or the
> display hardware.  Emacs never does anything like that.

It's almost definitely related to the fact that the NS port now draws
to an offscreen buffer on macOS 10.14 and above. Unfortunately the macOS
GUI toolkit has a reversed y axis as compared to what the Emacs code
expects. This means there are a number of places where we have to
invert the offscreen buffer, but I can't imagine a situation where
we're failing to invert it that wouldn't show up in normal usage.

There must be some specific situation that's catching it out.
-- 
Alan Third

bug#41187: 28.0.50; Flipped text

[Alan Third]

On Mon, May 11, 2020 at 01:00:57PM +0100, Wasim Abbas wrote:
> I am seeing this issue on emacs head. The text randomly flips
> vertically. Very hard to reproduce. But if you open a very long
> C/C++ file like
> https://github.com/KhronosGroup/Vulkan-Headers/blob/master/include/vulkan/vulkan_core.h
> <https://github.com/KhronosGroup/Vulkan-Headers/blob/master/include/vulkan/vulkan_core.h>
> and keep moving around the buffer, cut 100ish lines and paste in
> another location and then move around again. You might hit the
> issue.

I'm short on ideas with this, but can you tell whether the text that
displays upside down is text that was already on screen (and therefore
has probably been copied), or is newly drawn?
-- 
Alan Third

bug#41187: 28.0.50; Flipped text

[Alan Third]

On Sun, Aug 09, 2020 at 10:50:23AM +0100, Wasim Abbas wrote:
> Yes this is the text from the file I have opened.
> 
> I just did a quick test again today and I can reliably reproduce it.
> This time however it's not just flipped but corrupt frame buffer as
> it seems?
> 
> Here is what I have tried. Open up a longish C++ header file. Scroll
> with mouse a few times. Nothing happened. Split the window
> vertically and the scrolled a few more time rapidly. The corruption
> started in that window only. Visited another buffer in that window
> “messages” buffer you can see the flipped text there as well.
> 
> Visit the first window (is content was displayed correct so far, I
> think because its not refreshed yet) and move cursor up and down 1
> line at a time only that line is displayed wrong but also some other
> corruptions in random places.

It sounds suspiciously like we're flipping the bitmap and not
unflipping it, but I can't see how that happens.

Are you able to reproduce it with emacs -Q?
-- 
Alan Third

bug#41187: 28.0.50; Flipped text

[Wasim Abbas]

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No I can’t reproduce it with `emacs -Q`. I did mention when I started the issue "I haven’t tried with emacs -Q yet but happy to try if required.” But never did try this.

I thought since drawing buffers and rendering is such a core thing to emacs I wasn’t sure it will be anything else (like a package) but looks like it could be? Would you now think it's something to do with any package?

Is the standard disable each package one by one and see if it can be narrowed down to a single package the way to go forward now?

//Wasim

> On 9 Aug 2020, at 14:33, Alan Third <alan@idiocy.org> wrote:
> 
> On Sun, Aug 09, 2020 at 10:50:23AM +0100, Wasim Abbas wrote:
>> Yes this is the text from the file I have opened.
>> 
>> I just did a quick test again today and I can reliably reproduce it.
>> This time however it's not just flipped but corrupt frame buffer as
>> it seems?
>> 
>> Here is what I have tried. Open up a longish C++ header file. Scroll
>> with mouse a few times. Nothing happened. Split the window
>> vertically and the scrolled a few more time rapidly. The corruption
>> started in that window only. Visited another buffer in that window
>> “messages” buffer you can see the flipped text there as well.
>> 
>> Visit the first window (is content was displayed correct so far, I
>> think because its not refreshed yet) and move cursor up and down 1
>> line at a time only that line is displayed wrong but also some other
>> corruptions in random places.
> 
> It sounds suspiciously like we're flipping the bitmap and not
> unflipping it, but I can't see how that happens.
> 
> Are you able to reproduce it with emacs -Q?
> -- 
> Alan Third


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bug#41187: 28.0.50; Flipped text

[Alan Third]

On Mon, Aug 10, 2020 at 12:40:31PM +0100, Wasim Abbas wrote:
> I thought since drawing buffers and rendering is such a core thing
> to emacs I wasn’t sure it will be anything else (like a package) but
> looks like it could be? Would you now think it's something to do
> with any package?

It's unlikely to be a package directly causing it, but it may be doing
something which causes a bug in Emacs itself to show.

> Is the standard disable each package one by one and see if it can be
> narrowed down to a single package the way to go forward now?

The usual way would be a binary search type strategy. Comment out half
your config, then see if you still have the problem, if not try the
other half. Then you half what remains, and repeat until you've found
the cause.

The problem is that it may be a combination of things that are causing
it, but at least it may give us a chance to get a minimal recipe to
replicate the bug.
-- 
Alan Third

bug#41187: 28.0.50; Flipped text

[Wasim Abbas]

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Update:

Just managed to reproduce it with `emacs -Q` I just had to scroll for almost 10 minutes for it to kick in. So ignore my init.el red herring.

//Wasim

> On 17 Aug 2020, at 15:10, Wasim Abbas <abbas.wasim@gmail.com> wrote:
> 
> So I spend some more time on this today. Its painful to keep scrolling forever but I think I have found a pattern that works reliably.
> 
> Open emacs with a specific header file from command line. /usr/local/Cellar/emacs-head/HEAD-86fef6a_1/Emacs.app/Contents/MacOS/Emacs /personal/roar_engine/core/rhi/rorrhi_types.hpp
> M-x split-window-horizontally and start scrolling between the two windows interchangeably.
> 
> I did a binary search through my packages but it was inconclusive. It appeared with single package, but different single packages at different times. So I started commenting out my whole init.el file.
> 
> (setq user-full-name "Wasim Abbas")
> (setq user-mail-address "abbas.wasim@gmail.com <mailto:abbas.wasim@gmail.com>")
> 
> ;; load my sexp from elisp dir
> (add-to-list 'load-path (expand-file-name "elisp" user-emacs-directory))
> ;; add custom theme folder to load themes from ~/.emacs.d/themes
> (add-to-list 'custom-theme-load-path (expand-file-name "themes" user-emacs-directory))
> 
> This is the only snippet that I can reproduce it with. This doesn’t make much sense. I am not using any themes later on. The whole init.el is empty after these lines. I have reproduced it with this a few times.
> <Screenshot 2020-08-17 at 15.03.55.png>
> Although I have still not managed to reproduce it with `-Q` option yet.
> 
> Also at one point I got the following segfault.
> 
> <Screenshot 2020-08-17 at 15.03.05.png>
> 
> 
> //Wasim
> 
>> On 10 Aug 2020, at 20:11, Alan Third <alan@idiocy.org <mailto:alan@idiocy.org>> wrote:
>> 
>> On Mon, Aug 10, 2020 at 12:40:31PM +0100, Wasim Abbas wrote:
>>> I thought since drawing buffers and rendering is such a core thing
>>> to emacs I wasn’t sure it will be anything else (like a package) but
>>> looks like it could be? Would you now think it's something to do
>>> with any package?
>> 
>> It's unlikely to be a package directly causing it, but it may be doing
>> something which causes a bug in Emacs itself to show.
>> 
>>> Is the standard disable each package one by one and see if it can be
>>> narrowed down to a single package the way to go forward now?
>> 
>> The usual way would be a binary search type strategy. Comment out half
>> your config, then see if you still have the problem, if not try the
>> other half. Then you half what remains, and repeat until you've found
>> the cause.
>> 
>> The problem is that it may be a combination of things that are causing
>> it, but at least it may give us a chance to get a minimal recipe to
>> replicate the bug.
>> -- 
>> Alan Third
> 


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bug#41187: 28.0.50; Flipped text

[Alan Third]

On Mon, Aug 17, 2020 at 03:17:32PM +0100, Wasim Abbas wrote:
> Update:
> 
> Just managed to reproduce it with `emacs -Q` I just had to scroll
> for almost 10 minutes for it to kick in. So ignore my init.el red
> herring.

Hi Wasim, sorry for the long wait.

I've been trying to make some improvements to the performance of the
Emacs NS port, and I think they may help with this problem. Of course,
I'm not 100% sure the new code works anywhere except my PC yet, but if
you could give it a go that would be helpful.

I've pushed to a branch on the Emacs repository called
scratch/ns/performance. Please give it a go and see if it

1. works at all.

2. fixes your issue.

Thanks!
-- 
Alan Third

bug#41187: 28.0.50; Flipped text

[Alan Third]

On Sun, Dec 20, 2020 at 10:50:48AM +0000, Alan Third wrote:
> On Mon, Aug 17, 2020 at 03:17:32PM +0100, Wasim Abbas wrote:
> > Update:
> > 
> > Just managed to reproduce it with `emacs -Q` I just had to scroll
> > for almost 10 minutes for it to kick in. So ignore my init.el red
> > herring.
> 
> Hi Wasim, sorry for the long wait.
> 
> I've been trying to make some improvements to the performance of the
> Emacs NS port, and I think they may help with this problem. Of course,
> I'm not 100% sure the new code works anywhere except my PC yet, but if
> you could give it a go that would be helpful.
> 
> I've pushed to a branch on the Emacs repository called
> scratch/ns/performance. Please give it a go and see if it
> 
> 1. works at all.
> 
> 2. fixes your issue.

I've pushed this fix to the master branch and although I've only seen
the problem Wasim reported once, I expect this to have fixed it.

Wasim, if you're still seeing this problem, please reply to this email
and we'll reopen the bug report.

Thanks!
-- 
Alan Third

bug#41187: 28.0.50; Flipped text

[Wasim Abbas]

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Hi Alan,

Apologies for late reply, been away for a month.

Thanks for looking into this. I see your other email in which you mentioned you have closed the issue so just curious if the branch "scratch/ns/performance” still exists or its gone. I can’t find it `git://git.sv.gnu.org/emacs.git <git://git.sv.gnu.org/emacs.git%60>` <git://git.sv.gnu.org/emacs.git%60> or `https://git.savannah.gnu.org/git/emacs.gi` <https://git.savannah.gnu.org/git/emacs.gi%60> am I looking in the right place? There is also `https://github.com/emacs-mirror/emacs` <https://github.com/emacs-mirror/emacs%60> but it doesn’t have any `scratch/ns`.

Also did a quick search if this branch was merged in but failed to find anything relevant.

//Wasim


> On 20 Dec 2020, at 10:50, Alan Third <alan@idiocy.org> wrote:
> 
> On Mon, Aug 17, 2020 at 03:17:32PM +0100, Wasim Abbas wrote:
>> Update:
>> 
>> Just managed to reproduce it with `emacs -Q` I just had to scroll
>> for almost 10 minutes for it to kick in. So ignore my init.el red
>> herring.
> 
> Hi Wasim, sorry for the long wait.
> 
> I've been trying to make some improvements to the performance of the
> Emacs NS port, and I think they may help with this problem. Of course,
> I'm not 100% sure the new code works anywhere except my PC yet, but if
> you could give it a go that would be helpful.
> 
> I've pushed to a branch on the Emacs repository called
> scratch/ns/performance. Please give it a go and see if it
> 
> 1. works at all.
> 
> 2. fixes your issue.
> 
> Thanks!
> -- 
> Alan Third


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bug#41187: 28.0.50; Flipped text

[Alan Third]

On Wed, Jan 06, 2021 at 02:30:41PM +0000, Wasim Abbas wrote:
> Hi Alan,
> 
> Apologies for late reply, been away for a month.
> 
> Thanks for looking into this. I see your other email in which you mentioned you have closed the issue so just curious if the branch "scratch/ns/performance” still exists or its gone. I can’t find it `git://git.sv.gnu.org/emacs.git <git://git.sv.gnu.org/emacs.git%60>` <git://git.sv.gnu.org/emacs.git%60> or `https://git.savannah.gnu.org/git/emacs.gi` <https://git.savannah.gnu.org/git/emacs.gi%60> am I looking in the right place? There is also `https://github.com/emacs-mirror/emacs` <https://github.com/emacs-mirror/emacs%60> but it doesn’t have any `scratch/ns`.
> 
> Also did a quick search if this branch was merged in but failed to find anything relevant.

It was merged into master, but I squashed the commits so they likely
wouldn't look the same.

So if you could try the master branch and let me know if you still see
the problem, that would be great, thanks.
-- 
Alan Third

bug#41187: 28.0.50; Flipped text

[Wasim Abbas]

I am more than happy to try and test it out. Could you just confirm the repo to use. Thanks a lot. 

//Wasim 

Sent from my iPhone

> On 6 Jan 2021, at 18:33, Alan Third <alan@idiocy.org> wrote:
> 
> On Wed, Jan 06, 2021 at 02:30:41PM +0000, Wasim Abbas wrote:
>> Hi Alan,
>> 
>> Apologies for late reply, been away for a month.
>> 
>> Thanks for looking into this. I see your other email in which you mentioned you have closed the issue so just curious if the branch "scratch/ns/performance” still exists or its gone. I can’t find it `git://git.sv.gnu.org/emacs.git <git://git.sv.gnu.org/emacs.git%60>` <git://git.sv.gnu.org/emacs.git%60> or `https://git.savannah.gnu.org/git/emacs.gi` <https://git.savannah.gnu.org/git/emacs.gi%60> am I looking in the right place? There is also `https://github.com/emacs-mirror/emacs` <https://github.com/emacs-mirror/emacs%60> but it doesn’t have any `scratch/ns`.
>> 
>> Also did a quick search if this branch was merged in but failed to find anything relevant.
> 
> It was merged into master, but I squashed the commits so they likely
> wouldn't look the same.
> 
> So if you could try the master branch and let me know if you still see
> the problem, that would be great, thanks.
> -- 
> Alan Third

bug#41187: 28.0.50; Flipped text

[Alan Third]

On Wed, Jan 06, 2021 at 11:03:17PM +0000, Wasim Abbas wrote:
> I am more than happy to try and test it out. Could you just confirm the repo to use. Thanks a lot. 

git://git.sv.gnu.org/emacs.git
-- 
Alan Third

bug#41187: 28.0.50; Flipped text

[Wasim Abbas]

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Hi Alan,

TL;DR. I have tried master now and I can’t reproduce the issue anymore. Thanks a lot.

Details:

Built and run using
$ ./autogen.sh
$ ./configure
$ make  # this builds GNU Emacs 28.0.50 (build 1, x86_64-apple-darwin19.6.0, NS appkit-1894.60 Version 10.15.7 (Build 19H114)) of 2021-01-07
Ran using
$ ./src/emacs

Scrolled in different windows/frames for a quite a while but I can’t reproduce it anymore. I think we can safely assume its fixed.
I did see a different artefact, when you scroll too fast sometimes the screen looks like its not cleared from the previous text while the new text is printed onto it. But it doesn’t last for long only a fraction of a second. Probably unrelated and normal behaviour?

Thanks a lot again for your time.

//Wasim

> On 6 Jan 2021, at 23:22, Alan Third <alan@idiocy.org> wrote:
> 
> On Wed, Jan 06, 2021 at 11:03:17PM +0000, Wasim Abbas wrote:
>> I am more than happy to try and test it out. Could you just confirm the repo to use. Thanks a lot. 
> 
> git://git.sv.gnu.org/emacs.git
> -- 
> Alan Third


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bug#41187: 28.0.50; Flipped text

[Alan Third]

On Thu, Jan 07, 2021 at 10:47:45AM +0000, Wasim Abbas wrote:
> Hi Alan,
> 
> TL;DR. I have tried master now and I can’t reproduce the issue anymore. Thanks a lot.
> 
> Details:
> 
> Built and run using
> $ ./autogen.sh
> $ ./configure
> $ make  # this builds GNU Emacs 28.0.50 (build 1, x86_64-apple-darwin19.6.0, NS appkit-1894.60 Version 10.15.7 (Build 19H114)) of 2021-01-07
> Ran using
> $ ./src/emacs
> 
> Scrolled in different windows/frames for a quite a while but I can’t
> reproduce it anymore. I think we can safely assume its fixed. I did
> see a different artefact, when you scroll too fast sometimes the
> screen looks like its not cleared from the previous text while the
> new text is printed onto it. But it doesn’t last for long only a
> fraction of a second. Probably unrelated and normal behaviour?

Good to know it's fixed. Thanks.

As for the other problem, it shouldn't do that, but I'm not sure how
that would be happening. If it's a problem please open a new bug report.

-- 
Alan Third