[Metal] SwiftShot porting issues

[mykyta-bondarenko]

The original sample: https://developer.apple.com/documentation/arkit/swiftshot_creating_a_game_for_augmented_reality
Ported sample: https://github.com/xamarin/private-samples/tree/swift-shot/ios12/SwiftShot

• Download the ported sample
• Uncomment at least next lines:
  • 95
  • 118
  • 713
• Run the sample on a device

There is no changes on UI (flags should be animated). If you close the current game and start another one (without quiting the app) - scene view is stuck.
If you comment next line: flag.ParentNode.ReplaceChildNode(flag, clothNode); it will works as always.
I didn't find the reason of it. Could you help me with this issue?

[VincentDondain]

Hi, you sample have build issues with the latest commit 5b98738a53059eafd8ca898bb53cb1ca3bd97d98:

/Users/vince/Documents/private-samples/ios12/SwiftShot/SwiftShot/obj/iPhone/Debug/device-builds/iphone10.6-12.1/actool/cloned-assets/Assets.xcassets : actool warning : The image set "closePressed" has an unassigned child.
/Users/vince/Documents/private-samples/ios12/SwiftShot/SwiftShot/obj/iPhone/Debug/device-builds/iphone10.6-12.1/actool/cloned-assets/Assets.xcassets : actool warning : The image set "closePressed" has an unassigned child.
Core/Interactions/Projectile.cs(99,25,99,31): warning CS0108: 'Projectile.Create<T>(SCNNode)' hides inherited member 'GameObject.Create<T>(SCNNode)'. Use the new keyword if hiding was intended.
Core/Gameplay State/GameManager.cs(1474,25,1474,39): error CS1061: 'GameManager' does not contain a definition for 'flagSimulation' and no extension method 'flagSimulation' accepting a first argument of type 'GameManager' could be found (are you missing a using directive or an assembly reference?)
Core/Gameplay State/GameManager.cs(1476,26,1476,40): error CS1061: 'GameManager' does not contain a definition for 'flagSimulation' and no extension method 'flagSimulation' accepting a first argument of type 'GameManager' could be found (are you missing a using directive or an assembly reference?)
Core/Gameplay State/GameManager.cs(1477,26,1477,40): error CS1061: 'GameManager' does not contain a definition for 'flagSimulation' and no extension method 'flagSimulation' accepting a first argument of type 'GameManager' could be found (are you missing a using directive or an assembly reference?)
    3 Warning(s)
    3 Error(s)

Full build log: https://gist.github.com/VincentDondain/d7e10730814320609044b4fe33790550

[VincentDondain]

Ok didn't realize there was code to uncomment. Got it building, it makes my device restart... So yea I can confirm there's an issue. Investigating.

[VincentDondain]

I see some C3DMeshElementSetPrimitives invalid index buffer size and Execution of the command buffer was aborted due to an error during execution. <private>. Those seem to be the cause of the crashes.

Probably from https://github.com/xamarin/private-samples/blob/swift-shot/ios12/SwiftShot/SwiftShot/Core/Gameplay%20State/Flag.cs#L300-L339

[VincentDondain]

Mmh all the values in CreateFlagSimulationFromNode seem correct to me (was looking for matrices issues compared to the native code).

[VincentDondain]

Ok so I think it has to do with meshData.Geometry: https://github.com/xamarin/private-samples/blob/swift-shot/ios12/SwiftShot/SwiftShot/Core/Gameplay%20State/Flag.cs#L303 and probably https://github.com/xamarin/private-samples/blob/swift-shot/ios12/SwiftShot/SwiftShot/Core/Gameplay%20State/Flag.cs#L76-L168 (still pretty vague).

Doing var clothNode = SCNNode.FromGeometry (SCNPlane.Create (Width, Height)); (while not giving us the desired outcome) helps us avoid the errors I noted in
#4970 (comment).

[VincentDondain]

Ok progress, the buffers have some incorrect length due to the fact you're using SCNVector3.SizeInBytes (12 bytes) instead of Marshal.SizeOf (typeof (NVector3)) (16 bytes).

So 1 fix is to replace all SCNVector3 by NVector3 in https://github.com/xamarin/private-samples/blob/swift-shot/ios12/SwiftShot/SwiftShot/Core/Gameplay%20State/Flag.cs#L76-L168 but unfortunately that's not enough to fix the entire problem.

Need to investigate more.

[mykyta-bondarenko]

@VincentDondain shouldn't we convert it to the bug?

[VincentDondain]

Hi, no sorry we still need to investigate more to pinpoint specific issues (bug), I haven't had time to get back to it.