MacOS – Where does a screenshot come

displaygpumacosscreen capture

I've a problem with my Mac Mini.
Sometimes, from some time, it displays some glitches, or "graphical problems", for instance the screenshot below shows some bands in a part of the screen with black or "rainbowed" flashing pixel and sometimes, when Mac wake up from sleep, all screen has a green tint. Everything solves sleeping and waking up the Mac.

I was convinced that it's a GPU problem but I went to Genius bar with these screenshot and they told me that "screenshot comes from the screen, not from the GPU, so, if glitch appears even in screenshot, problem is in the screen or the cable, not in the Mac", is it true?

Best Answer

Your Genius was misinformed. When graphical artifacts or distortions show up in a screenshot, they are a product of the graphics card. It is one of the quickest tests, we did it all the time to classify graphics issues. Most geniuses know this, like I said you got someone who was either new or off their game that day.

Long story short, you're absolutely right that it's the GPU.

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MacBook – Scrambled screen when going out of sleep

Although it's likely a hardware issue, you could try a few things if you don't want to get hardware help from Apple yet.

See if this happens when booting in Safe Mode.
Install a clean OS on an external drive to be sure it's not some extension or conflict.
Look in the console logs - see if you can see any obvious errors.
Try with other monitors and cables - it could be a bad cable or display. An EFI or firmware update might be needed to make the mac handle this situation better (it should never freeze) - and a report to Apple with details how to reproduce this might help get a fix sooner unless others have reported this specific combination.
If you have alternate RAM - do try swapping that in for testing. The newest macs use RAM heavily for display buffering - and wake from sleep is a time when you first can see issues with RAM going bad.

I'm lucky to have stores close by and would head there for a diagnostic checkup - so keep that in mind - it could just be a hardware failure / bad RAM, but anything you can do to narrow down the cause or rule out software / accessories by disconnecting everything but the bare minimum could save you a trip to the shop.

How to wake the screen from terminal

That sounds like your Mac is actually sleeping (suspend-to-ram) and not just turning it's screen off. If the screen was just turned off, simulated mouse/keyboard input from Synergy should wake it back up. If it's sleeping it won't, because your Mac isn't listening for Synergy network traffic when asleep.

You can either adjust the power save settings to only turn the screen off, but not actually go to sleep (but then you're sort of already doing that via Caffeine when you remember to) or wake the Mac via a Wake-on-LAN magic packet that will awaken it even from sleep mode, which can be sent from a command-line utility on the Windows machine.

If that doesn't work to your satisfaction you can also wake the Mac up in scheduled intervals via pmset (see man pmset for more information). For example, to wake up every Monday to Friday at 8:30am:

 pmset repeat wake MTWRF 08:30:00

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MacBook – Scrambled screen when going out of sleep

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