Scaling Macbook Resolution on an Ultrawide in HiDpi

So bit of background. I like Mac's retina (otherwise known as HiDPI under the hood) display. Even when on a non-native resolution, I feel its sharper than running on the low DPI setting.

I've bought monitors in the past (a lovely Dell, 2560x1440) and had to cave to the fact that I could not run retina/HiDPI at anything more than 1650x1080, and have black bars left and right of the main screen.

Well struggle no more. I have found a solution, and it stems from the fact that I bought a new Iiyama 3440x1440 Ultrawide.

When it runs at native resolution, it looks ok, very slightly blurry fonts, and the terminal never looks quite right to me, so wanted to have another go at trying to go full retina on it.

The secret sauce is located at this github: https://github.com/xzhih/one-key-hidpi

(A couple of links led me to this: https://www.youtube.com/watch?v=SmVjRkgFvII and https://medium.com/@jmiller180/hey-james-came-across-your-article-and-thought-i-would-share-something-that-i-discovered-when-fab4e60abb0. Problem with these is that they were for Catalina and didn't work on Big Sur and needed SwitchResX which I've had issues with before)

The result is I can get about a 135% scaling, with HiDPI and fonts look reasonably clear. Awesome.

So what do we do.

First we clone the github repo:

1git clone https://github.com/xzhih/one-key-hidpi

...then sudo up (I've run this a couple of times now since the intial discovery without having to sudo), and run the script

1sudo -s
2./hidpi.sh

I choose Option 1 to Enable HiDPI

 1  _    _   _____   _____    _____    _____ 
 2 | |  | | |_   _| |  __ \  |  __ \  |_   _|
 3 | |__| |   | |   | |  | | | |__) |   | |  
 4 |  __  |   | |   | |  | | |  ___/    | |  
 5 | |  | |  _| |_  | |__| | | |       _| |_ 
 6 |_|  |_| |_____| |_____/  |_|      |_____|
 7                                           
 8============================================
 9
10(1) Enable HIDPI
11(2) Enable HIDPI (with EDID)
12(3) Disable HIDPI
13
14Enter your choice [1~3]: 1

then Option 6 Do Not Change for the display icon (I think this is the icon Mac chooses to show in display pref)

 1-------------------------------------
 2|********** Display Icon ***********|
 3-------------------------------------
 4
 5(1) iMac
 6(2) MacBook
 7(3) MacBook Pro
 8(4) LG Display
 9(5) Pro Display XDR
10(6) Do not change
11
12Enter your choice [1~6]: 6

...and then finally, option 6 Manual input resolution, entering in 2560x1440 when it asks.

 1------------------------------------------
 2|********** resolution config ***********|
 3------------------------------------------
 4(1) 1920x1080 Display
 5(2) 1920x1080 Display (use 1424x802, fix underscaled after sleep)
 6(3) 1920x1200 Display
 7(4) 2560x1440 Display
 8(5) 3000x2000 Display
 9(6) Manual input resolution
10
11Enter your choice: 6 
12Enter the HIDPI resolution, separated by a space，like this: 1680x945 1600x900 1440x810
13:2560x1080
14Enabled, please reboot.
15Rebooting the logo for the first time will become huge, then it will not be.

and thats it. When I'm on my main ultrawide monitor I can set the display res to 2560x1080 hidpi using RDM!

Not had a problem with it so far on two different Macs. The 2015 does well (altho don't think it can quite hit 100Hz, so I leave it at 60Hz)