In my measurements, I've found that the mirror app can take up to 11ms of time on a per-frame basis. For many games, its performance may be fine, but for action games (often running at 40+ FPS (50 in my case), with full screen redraws), it isn't usable in my opinion.
To this end, it would be useful to have a programmatic way to detect mirror usage, either to disable it as a developer, or to tweak game behavior to accommodate its poor performance.
+1 on this. The game I'm working on now runs at 50 fps on hardware and its performance is very sub-par with Mirror. I'm considering adding a "mirror mode" option to compensate for the reduced frame rate, but even then the game does not shine running under Mirror's limitations.
Hmm, I wonder.
If its possible to have separate screens for both Playdate and the Mirror app.
Kinda like a proto Game Boy Advance to GameCube adapter. However, I doubt its possible to render two screens at once and plus ruins the simplicity of the Mirror app. But yes, Mirror performance is a bit... heavy. I played Boogie Loops from Season 1 and it is, extremely slow on Mirror. Mostly due to particles.