Am currently debugging compatibility issues with my OpenGL ES 2.0 shaders across several different Android devices.
One of the biggest problems I'm finding is how the different precisions in GLSL (lowp, mediump, highp) equate to actual precisions in the hardware. To that end I've been using glGetShaderPrecisionFormat to get the log2 of each precision for vertex and fragment shaders, and outputting this in-game to the game screen.
On my PC the precision is coming back as 23, 23, 23 for all 3 (lo, medium, high), running under linux natively, or the Android Studio emulator. On my tablet, it is 23, 23, 23 also. On my phone it comes back with 8, 10, 23. If I get a precision issue on the phone I can always bump it up to the next level to cure it. However, the fun comes on my android TV box (Amlogic S905X) which seems to only support 10, 10, 0 for fragment shaders. That is, it doesn't even support high precision in fragment shaders.
However being the only device with this problem it is incredibly difficult to debug the shaders, as I can't attach it via USB (unless I can get it connected via the LAN which I haven't tried yet). I'm having to compile the APK, put it on a usb stick, take into the other room, install and run. Which is ridiculous.
My question is what method do other people use to debug these precision issues? Is there a way to get the emulator to emulate having rubbish precision? That would seem the most convenient solution (and if not, why haven't they implemented this?). Other than that it seems like I need to buy some old phones / tablets off Ebay, or 'downgrade' the precision in the shader (to mediump) and debug it on my phone...