HiDPI Resolution Limited with HDMI 1.4 - Bandwidth Question

[redapple0204]

I'm trying to enable HiDPI on my external 2K (2560x1440) display connected to my Mac via an HDMI 1.4 cable. My goal is to achieve a HiDPI resolution of 2048x1152.

However, I've encountered a limitation. I can successfully enable HiDPI up to around 1400x800. When I try to select a higher resolution (like 2048x1152) and click the HiDPI toggle in BetterDisplay, it doesn't seem to work. The HiDPI mode doesn't activate, and the display remains in a non-HiDPI mode.

I've noticed that the maximum resolution where HiDPI does work (around 1400x800) is roughly half the maximum bandwidth capacity of HDMI 1.4. For example, 1400x800 doubled is approximately 2800x1600, which seems to be close to the limit of what HDMI 1.4 can handle at a reasonable refresh rate (60Hz in my case).

My main question is: Does enabling HiDPI for a specific resolution effectively require double the bandwidth of that resolution?

In other words, if I want to use 2048x1152 in HiDPI mode, does BetterDisplay (or macOS's display scaling) require the GPU and the HDMI connection to output a resolution equivalent to 4096x2304 (2048x1152 * 2)? If this is the case, it would explain why I'm hitting a limit with HDMI 1.4, as it likely cannot support the bandwidth required for the doubled resolution.

[waydabber]

No, HiDPI rendering affects the framebuffer (video memory) only, so timing bandwidth constraints are not relevant. If you are using an Intel Mac with Intel iGPU, some custom HiDPI resolutions might randomly not work sometimes (other times they might work). It's a known driver bug with Intel iGPU Macs.