(Help needed) External USB Screen Blanking On Mouse Pointer Change

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2019-06-15 20:58:38

MacBook (Retina, 12-inch, Early 2015) (Integrated Intel HD Graphics 5300)
MacOS 10.14.5
Pixelmator Pro 1.3.4
LG Ultrafine Display 24MD4KL connected over USB

I've found the weirdest/most specific bug/interrop problem and I thought I'd see if pick the brains of both Pixelmator support and the Pixelmator Pro community at the same time and see if anybody can help me troubleshoot/reproduce this. If you have a second monitor I'd really appreciate it if you could test it on your setup and let me know if you see the problem.

When I'm using a 50px brush and am zoomed in to 400% and the mouse pointer changes from a brush to a mouse pointer the external screen blanks for about three seconds (as if the monitor has just been connected). Moving the mouse pointer off the canvas or hitting the command button triggers this. It doesn't happen every time but does happen consistently enough that 15 presses of the command key should indicate the problem (the most I've got to so far has been eight).

To reproduce:
1. Open Pixelmator Pro.
2. Move the Pixelmator Pro window onto the extenal screen (if using a laptop). If you're using a desktop with multiple screens, just try wherever.
3. Create a new 1000px by 1000px image at 72ppi with 8-bit colour (I've seen it with various resolutions but I can confirm that it happens with these settings).
4. Select the brush tool and the 50px basic brush (I've seen it with various brushes and brush sizes between 40px and 60px so 50px should trigger it if it's going to happen)
5. Zoom into 400%.
6. Move the mouse onto the canvas so that the brush circle shows.
7. Keeping the mouse over the canvas, press the Command key (⌘) to show the mouse pointer then release to return to the paint circle. Press ⌘ once a second for about fifteen seconds. That should either show the problem or give you the all clear.

1. It really is about the size of the circle as it appears on screen. If It reduce the brush size to 25 pixels at a zoom of 400% the problem no longer occurs but if I zoom in to 800% with a 25px brush I see the problem again.
2. If I move the Pixelmator Pro window back to my laptop screen I no longer see the problem.
3. I've got my external screen scaled to show a bit more content (the middle of the size options), but I just switched it to default and the problem was still there.

Any advice or results with different hardware much appreciated. I'll update this if I find out more.
Hope you can help.
- Stef.
Update: Also happens with the Clone tool at 29% to 59% regardless of zoom. Strangely, larger sizes are fine.
Update: I’m not seeing anything happening in Console but I’m not really sure what I should be looking for.
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2019-06-17 10:00:54

Hey Stef, thanks for the very detailed bug report! This is actually a known, fairly long-standing system cursor issue that is periodically fixed and then reappears again. We've reported this to the good folks at Apple but it would help if you could also file a report using the Feedback Assistant and give us the reference number you get so we can add it to our report.
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2019-06-17 10:16:30

Thanks for the quick response, Andrius. I'll file a report with Apple.
Can you let me know what kind of hardware that has caused this problem in the past? Is it Intel embedded graphics? Second displays? USB/Firewire displays? Or some combination?
(Because I'm on the verge of sending the display back, cancelling my order of a Mac Mini and ordering an iMac instead. I'd just like to choose the hardware that is least likely to see a problem like this.)
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2019-06-17 10:40:22

We're not 100% sure though we suspect it's related to Intel integrated graphics as we haven't been able to reproduce this particular bug with other set-ups (Radeon/Nvidia GPUs). So if you've ordered yourself a new Mac mini, it's possible you might have this. However, that mini has a 9th gen GPU and my colleague just tried it on her new MacBook Air (also with a 9th gen GPU) and couldn't reproduce it. So we've only been able to repro this on 7th and 8th gen Intel integrated GPUs. With all that in mind, I'd say you don't need to worry about sending the display back and you'll probably be fine with the mini. But, you know, it's your call.
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2019-06-17 10:57:07

Oh, another important point — it doesn't have to be an external display, it's a matter of the resolution, though we're not certain whether that's the resolution of the screen or the image. But basically, it's related to the physical size of the cursor on the screen and the resolution of one of those two things. That might be why you're not seeing it on your MacBook display, though there are probably some conditions that might make the bug happen. And the screen flashing duration varies. On some systems, it's as long as you're seeing, on others, it can be under a second.
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2019-06-17 11:04:28

My Apple feedback number is FB6161401
we haven't been able to reproduce this particular bug with other set-ups (Radeon/Nvidia GPUs)
iMac it is, then. I can get a similarly specced iMac (only with a Radeon GPU instead of Intel Graphics) for less than the Mini plus monitor. The thing that finally tipped the scales onto the Mini was the ability to use the display with other devices (including my MacBook).

I hate interop problems. Wishing you and the devs the best of luck and lots of patience.
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2019-06-17 11:57:32

Cheers for that number — I've passed it on to our lead dev.

I have a feeling you would've been fine with the mini (again, 9th gen GPUs don't appear to have this issue). We're also looking for workarounds in the meantime. But it's totally your call, I just don't want to feel like we've scared you into getting a different set-up.
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2019-06-17 13:28:32

It's a healthy mix of caution and pragmatism (with just a small dash of fear). I've never been a fan of on-board video but the interop problem has made me want a separate graphics card/chip more than before. The balance of the equation has changed and a Mac Mini is no longer the right machine for me.

Thanks again for your replies. I've spent the weekend alternating between trying to figure out the problem and being annoyed/upset about it. Time to order myself an iMac.