Panic’s digital A/V adapter teardown inspired me to write down some of my own findings with the adapter that now make a little more sense.
When connected with a passthrough, the device doesn’t show up in Xcode, Image Capture, etc. This is frustrating because I can’t see console messages for debugging but at least I can do most of my testing using an AppleTV which I CAN use while connected to Xcode
The adapter tries to use a display’s native resolution, which it does as long as you’re not using something that accepts higher resolutions (TVs and projectors that are 1366×768 or 1280×800 often accept 1080p input and do their own scaling). When you programmatically try to set it to something else, it resizes the context and stretches it via software.
It doesn’t actually let a developer see a display’s actual resolutions. When I use the old digital A/V adapter on this 1600×1200 display, I get 1280×1024 (5:4 ratio) as a choice. When using the new A/V adapter, I don’t get it anymore, and instead get 1200 x 900 (4:3, like the display actually is). Interestingly, although the new A/V adapter sets its output to 1600×1200, 1600×1200 is not a choice in the list, so no matter what I do things will be scaled.