Acorn on my iMac screen

Using the last release on my iMac , my screen flashes !!!
Any idea ?
Thanks a lot’é

Well that’s super interesting. If you look a still shot of the flash, it’s not the whole screen, but rather it’s the canvas:

Can you tell me if you have a selection on the canvas when the flash occurs? It doesn’t look like you do, but I can’t think of any reason why the canvas would want to all of a sudden change things up.

And one other thing to try- if you open up Acorn’s Preferences, click on “Fussy Stuff”, and change the Renderer: option from Metal to OpenGL, does the problem still occur?



Hello, I’m evaluating version 6 (currently have 4.5) and I’m experiencing flashing screen when a selection is active as well. Very distracting.

When I switch from OpenGL to Metal (not recommended for my GPU) the flashing seems to stop, but the performance is not very smooth.

This is on a 2013 MacBook Pro i7, 16gb ram, SSD, nvdia 750m running Mojave.

Are my choices deal with the constant screen flash when a selection is active, or deal with poor performance, or upgrade my laptop, or stick to the version I have?

The selection flickering is a known issue with that hardware + OS. I’ve looked for a workaround, but without any luck so far. Unfortunately I think the bug is going to be for Apple to fix (and maybe they have already- I haven’t checked the status of this bug on 10.15… but they also have decided OpenGL and Nvidia isn’t the future for the Mac, and doesn’t seem to be putting too much effort into fixing things with that combo).

So I don’t have a good solution for you right now, but as soon as I can figure out a fix for the OpenGL selection flickering it it’ll be added to Acorn.

Thanks for the clarification. I had figured as much. This isn’t the first time Apple has screwed me over for having an nvidia gpu lately.

If it weren’t for the new keyboards and trackpads being so awful I’d be more tempted to upgrade. Though it’s been more a case of MacOS updates making things stop working and hurting performance than the age of the laptop would suggest.

I like Acorn and would like to upgrade but with the current situation I can’t see it happening.

Thanks for your time.

I’m having the same problem with a GeForce GT 650M in a 2012 (10,1) MacBook Pro, on both in laptop’s display and any external monitors. It really is a flustering behavior.

@meyerweb Can you tell me what version of MacOS you’re running?

@ccgus Sorry, missed this under all my GitHub notifications. I’m on the latest Mojave, 10.14.6. I’ve never run Acorn under any other major OS version (just bought Acorn a week or so back) so unfortunately I can’t compare it with past OS versions.

@meyerweb Thanks for the update. I think I have access to this particular machine somewhere around here… I’ll take a look and see if I can reproduce it.

I don’t know if this helps in any way, but I only see it when using marching-ants selection mode. The clipped-out mode doesn’t seem to have the same problem.

The reason is probably because the ants require constant redrawing, which is going to induce the flickering at some point. The clipped-out version just draws it once when set.