This is going to disrupt a lot of developers and game engines that are built on OpenGL. Many are scrambling to start porting over now as they fear the inevitable that Apple will discontinue support entirely come iOS 13.
@Paul, a couple potential solutions that other engines and developers have discussed but neither sound too good to me:
1.) Integrate Vulkan renderer and then explore
MoltenVK which provides transparent translation to Metal on iOS devices. The obvious downsides being this solution requires OpenGL ES 3.1, Android 7.0 etc. so older devices will no longer be supported (only about 37% of Android devices support it currently). Metal itself also is only supported on the A7 and newer Apple chips so also won't be as compatible as AppGameKit currently is with older devices. I think integrating Vulkan might be a huge undertaking to an existing OpenGL framework like AGK.
2.) Check into
MoltenGL - This sounds like a good solution to ease porting as it seamlessly switches to Metal on supported devices without affecting OpenGL syntax. However, it is a commercial product and very expensive ($600 for a five-seat license although they do also offer volume/OEM licensing but no details of how expensive that is). A free trial is available.
Most of the frameworks have worked to manually integrate Metal and fallback to OpenGL on non-Apple and unsupported devices. But it really is a large undertaking I'm afraid.
