After being able to link Vulkan libraries in our Xcode iOS project, we are finally able to write Vulkan code for iOS. To use Vulkan with iOS, we need to give Vulkan the pixel buffer area for the screen. Usually this is done through something like HWND for DirectX, but with iOS we cannot get that low to a raw window pointer. So Vulkan asks for a UIView pointer, but not just any UIView. The one that you give to Vulkan must have a backing layer if CAMetalLayer or something that derives from CAMetalLayer. In MacOS this is an easy thing to achieve, just grab the NSWindow and say that it's backing layer is Metal, but in iOS, it gets a bit messy.
iOS UIviews are layer-backed, meaning that they are given a layer upon creation and you absolutely cannot change it after (unless you write a custom View controller). This creates a conflict for Gateware. We want the user to be able to create a UIView themselves if they wish and still be able to use Vulkan, but we cannot change what they have specified. It is possible to run 2 controllers at the same time, or even just 2 views on the same controller. This solution has its drawbacks too. Since Gateware is usually used for games, this extra view or controller would be unecessarily using system resources. There must be a solution where the user can create a window but have Gateware put Vulkan into it.
This is where I had an idea, if we cannot change the current view, can we change the current view controller? The answer was simple, as long as you present the view once you are done swapping them, the newly created view would be the one that is visible, and on top. So I had decided to create a Gateware View and View controller that had support for Metal. Next was just to detect whether or not the users View was Metal capable and overwrite it if not. This allows easy access for people wanting to develop Vulkan for their games and a level of control for people that already have a game looking to use Gateware.
I am glad to say that the effort paid off. After fiddling around with some of the desktop Unit Tests, (and some incorrect file IO pathing) I was able to run them on iOS Simulator and an iPhone 7 running iOS 13. It feels nice to finally be done with Vulkan and to move on to Audio.
References:
MoltenVK
https://github.com/KhronosGroup/MoltenVK
UIKit UIViewController
https://developer.apple.com/documentation/uikit/uiviewcontroller
UIKit UIView
https://developer.apple.com/documentation/uikit/uiview
Metal CAMetalLayer
https://developer.apple.com/documentation/quartzcore/cametallayer
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