AppleARKit forces view projection matrix according to device viewport

[Link Removed]

 

Per UDN case: 

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As of UE 5.4.3 hot-fix release. On iOS, using ARKit.

We can't change the Camera Component's FOV. Ultimately, this is because FAppleARKitCamera::SetupViewProjectionMatrix() now /always/ forces the view projection matrix according to the device's viewport dimensions.  

But in our app here, we simulate different cameras, filmbacks, focal lengths.. ultimately our own FOV. So we need to be able to arbitrarily change the FOV of the Camera Component. We alter the live video ourselves to match - scaling it up or down - and dealing with any "out of FOV" regions of the live video image in a particular manner, as needed.  

 

My hack isn't great, but gets the job done for now -  

AppleARKitSystem.h - Add a public bool on FAppleARKitSystem to control whether to allow this new behaviour, or skip it. Set to true by default.  

 

AppleARKitSystem.cpp - In FAppleARKitXRCamera::SetupViewProjectionMatrix(), checking this new bool on FAppleARKitSystem.. f true - works as current implementation. If false - returns immediately (like previous implementation, which called FDefaultXRCamera::SetupViewProjectionMatrix() which did nothing.. but I should in fact call this function too, even though it does nothing.)  

In my app, I get the ARKitSystem and set this new bool to false.```