Will this result in double the monitor output performance?（dummy and real）

[li0926]

[waydabber]

Hi @li0926 - the app does not physically increases the number of pixels on your display - if you use a dummy with HiDPI resolution and mirror it to your non-HiDPI display, the number of pixels on your display will remain the same, only the framebuffer (the representation of the screen inside your Mac's memory) will increase in quality. This is useful for scaling purposes (when you want to have an in-between resolution, one that does not match your display's physical resolution exactly), creating snapshots, zooming etc.

[li0926]

I know what you said.
What I want to ask is, macbook output image to the display, it takes CPU/GPU/framebuffer resources, if I use dummy, will this lead to more resource consumption?
(I mean：
Do not use dummy: output one physical display;
Use dummy: output one dummy and one physical display？？ right？double cpu/gpu/framebuffer resource consumption？)
Thanks！

[waydabber]

If you are not mirroring the dummy, then yes, you'll use double the framebuffer. If you mirror the dummy the system should be using a single common framebuffer on M1 (as the OS reports this mirror as a hardware mirror) but I did not do actual tests regarding to this. The reason is that framebuffer memory usage is rather low in practice actually since even a 5K 32 bit framebuffer will consume about 56 megabytes of RAM and even if there is buffering it will be 100-150 megabytes tops which is negligible (even on the lowest specced 8GB M1 systems). Desktop composition might require more GPU memory but even that is not that taxing on M1 as the GPU is super efficient in doing metal things. Handling and copying from framebuffer to framebuffer (or framebuffer to a window view surface) also requires minimal resources as on M1 everything happens inside the chip. So even if you are not mirroring but streaming or use a PIP window, you should not notice any serious performance impact (maybe the input lag will increase a bit which might affect high performance gaming). On Intel machines things are different though and performance impact varies from machine to machine. Intel UHD generally struggles even at rendering basic macOS effects (like transparency) on a 4K desktop running at 60Hz. With discrete graphics much more inter CPU-GPU communication is necessary but AMD drivers don't seem to implement virtual display mirroring properly anyway.

[li0926]

Ok, I got it, thank you for your serious reply