So this doesn't seem like a productive avenue. It also introduces a lot of bugs-layers on macOS are not as fully baked as they are on iOS. You also lose the ability to blur the contents behind the window, which is very popular.

Using layers helps on some machines and hurts on others. The deprecated core graphics API is significantly faster, but it does a not-so-great job at anything but ASCII text, doesn't support ligatures, etc. Using Core Text, it can easily take over 150ms to draw a single frame for a 4k display on a 2015 macbook pro. If I could draw a whole frame in a reasonable amount of time, this problem would be much easier! But I can't. So it's tricky to get right, especially considering how slow macOS's text drawing is. But there have also been a handful of complaints that latency was too low-when you hit return at the shell prompt, the next frame drawn should include the next shell prompt, not the cursor on the next line before the new shell prompt has been read. I'm sure there are some low-hanging fruit here. I'll spend some time looking into iTerm2's latency.

Online terminal emulator mac