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Red flashing screen around viewport after switching displays on Mac
Needs Triage, NormalPublic


System Information
Operating system: Mac OS MoJave
Graphics card: Radeon Pro 560X 4 GB

Blender Version
Broken: v2.82a
Worked: N/A

When using blender 3d on a mac laptop, with a secondary monitor plugged in, I often use my HDMI switch to swap to and from my laptop to my PC. When I go to my PC, then back to my laptop, blender has a flashing strobing red area around my viewport. And also I cannot click into the area of blender, since my mouse is off focus. (can't click the actions in the dialog box to quit blender)

Exact steps for others to reproduce the error

  1. Open Blender 3D on mac, using it on a secondary monitor connected on a HDMI switch.
  2. Switch to another computer using the hdmi switch.
  3. Switch back to mac os using the hdml switch.
  4. Open Blender 3d.
  5. flashing red appears.

Based on the default startup or an attached .blend file (as simple as possible).

Event Timeline

Try a newer version
There have already been fixes for similar issues.

Germano Cavalcante (mano-wii) changed the task status from Needs Triage to Needs Information from User.EditedDec 3 2020, 2:25 PM

Blender v2.82a is no longer being maintained.
Please "test with the latest official release from and daily build from"

I have downloaded and installed the daily build and the error is still happening. Here is screenshot proof. December 3rd, 2020. Can upload video recording if you require it.

Germano Cavalcante (mano-wii) changed the task status from Needs Information from User to Needs Triage.Dec 3 2020, 8:30 PM
  • Are there any issues when you turn the monitor off and on?
  • When you switch your monitor to PC, how does macOS see it? (The monitor is not connected, or something else.)
  • 2560px is the resolution for Mac, is 1680px the screen resolution when you use a PC?

I can't test it, but it seems that Blender doesn't respond to changes in monitor settings or on/off. And probably when automatically (not manually by the user) the window is moved to another screen. So I would just try, similar to what we do for windowDidChangeBackingProperties, the same for NSApplicationDidChangeScreenParametersNotification and NSWindowDidChangeScreenNotification. Or something like that.

NSApplicationDidChangeScreenParametersNotification. The system posts this notification when the Mac's display configuration changes; for example, when the user connects or disconnects an external display from the system.

NSWindowDidChangeScreenNotification. The system posts this notification when any window, including the window containing your view, moves to a different display.

There are very similar reports T73373 T67923 T57069 ... closed but I'm not sure they are resolved though.

Sorry I've been a little delayed on this ticket.

Will it help if i film my screen to show you the errors?