PassthroughFBExt.cs

using System;
using System.Runtime.InteropServices;

namespace StereoKit.Framework
{
	class PassthroughFBExt : IStepper
	{
		bool extAvailable;
		bool enabled;
		bool enabledPassthrough;
		bool enableOnInitialize;
		bool passthroughRunning;
		XrPassthroughFB      activePassthrough = new XrPassthroughFB();
		XrPassthroughLayerFB activeLayer       = new XrPassthroughLayerFB();

		Color oldColor;
		bool  oldSky;

		public bool Available => extAvailable;
		public bool Enabled { get => extAvailable && enabled; set => enabled = value; }
		public bool EnabledPassthrough { get => enabledPassthrough; set {
			if (Available && enabledPassthrough != value) {
				enabledPassthrough = value;
				if ( enabledPassthrough) StartPassthrough();
				if (!enabledPassthrough) EndPassthrough();
			}
		} }

		public PassthroughFBExt() : this(true) { }
		public PassthroughFBExt(bool enabled = true)
		{
			if (SK.IsInitialized)
				Log.Err("PassthroughFBExt must be constructed before StereoKit is initialized!");
			Backend.OpenXR.RequestExt("XR_FB_passthrough");
			enableOnInitialize = enabled;
		}

		public bool Initialize()
		{
			extAvailable =
				Backend.XRType == BackendXRType.OpenXR &&
				Backend.OpenXR.ExtEnabled("XR_FB_passthrough") &&
				LoadBindings();

			if (enableOnInitialize)
				EnabledPassthrough = true;
			return true;
		}

		public void Step()
		{
			if (!EnabledPassthrough) return;

			XrCompositionLayerPassthroughFB layer = new XrCompositionLayerPassthroughFB(
				XrCompositionLayerFlags.BLEND_TEXTURE_SOURCE_ALPHA_BIT, activeLayer);
			Backend.OpenXR.AddCompositionLayer(layer, -1);
		}

		public void Shutdown()
		{
			EnabledPassthrough = false;
		}

		void StartPassthrough()
		{
			if (!extAvailable) return;
			if (passthroughRunning) return;
			passthroughRunning = true;
			
			oldColor = Renderer.ClearColor;
			oldSky   = Renderer.EnableSky;

			XrResult result = xrCreatePassthroughFB(
				Backend.OpenXR.Session,
				new XrPassthroughCreateInfoFB(XrPassthroughFlagsFB.IS_RUNNING_AT_CREATION_BIT_FB),
				out activePassthrough);

			result = xrCreatePassthroughLayerFB(
				Backend.OpenXR.Session,
				new XrPassthroughLayerCreateInfoFB(activePassthrough, XrPassthroughFlagsFB.IS_RUNNING_AT_CREATION_BIT_FB, XrPassthroughLayerPurposeFB.RECONSTRUCTION_FB),
				out activeLayer);

			Renderer.ClearColor = Color.BlackTransparent;
			Renderer.EnableSky  = false;
		}

		void EndPassthrough()
		{
			if (!passthroughRunning) return;
			passthroughRunning = false;
			
			xrPassthroughPauseFB       (activePassthrough);
			xrDestroyPassthroughLayerFB(activeLayer);
			xrDestroyPassthroughFB     (activePassthrough);

			Renderer.ClearColor = oldColor;
			Renderer.EnableSky  = oldSky;
		}

		#region OpenXR native bindings and types
		enum XrStructureType : UInt64
		{
			XR_TYPE_PASSTHROUGH_CREATE_INFO_FB = 1000118001,
			XR_TYPE_PASSTHROUGH_LAYER_CREATE_INFO_FB = 1000118002,
			XR_TYPE_PASSTHROUGH_STYLE_FB = 1000118020,
			XR_TYPE_COMPOSITION_LAYER_PASSTHROUGH_FB = 1000118003,
		}
		enum XrPassthroughFlagsFB : UInt64
		{
			None = 0,
			IS_RUNNING_AT_CREATION_BIT_FB = 0x00000001
		}
		enum XrCompositionLayerFlags : UInt64
		{
			None = 0,
			CORRECT_CHROMATIC_ABERRATION_BIT = 0x00000001,
			BLEND_TEXTURE_SOURCE_ALPHA_BIT = 0x00000002,
			UNPREMULTIPLIED_ALPHA_BIT = 0x00000004,
		}
		enum XrPassthroughLayerPurposeFB : UInt32
		{
			RECONSTRUCTION_FB = 0,
			PROJECTED_FB = 1,
			TRACKED_KEYBOARD_HANDS_FB = 1000203001,
			MAX_ENUM_FB = 0x7FFFFFFF,
		}
		enum XrResult : UInt32
		{
			Success = 0,
		}

#pragma warning disable 0169 // handle is not "used", but required for interop
		struct XrPassthroughFB      { ulong handle; }
		struct XrPassthroughLayerFB { ulong handle; }
#pragma warning restore 0169

		[StructLayout(LayoutKind.Sequential)]
		struct XrPassthroughCreateInfoFB
		{
			private XrStructureType             type;
			public  IntPtr                      next;
			public  XrPassthroughFlagsFB        flags;

			public XrPassthroughCreateInfoFB(XrPassthroughFlagsFB passthroughFlags)
			{
				type  = XrStructureType.XR_TYPE_PASSTHROUGH_CREATE_INFO_FB;
				next  = IntPtr.Zero;
				flags = passthroughFlags;
			}
		}
		[StructLayout(LayoutKind.Sequential)]
		struct XrPassthroughLayerCreateInfoFB
		{
			private XrStructureType             type;
			public  IntPtr                      next;
			public  XrPassthroughFB             passthrough;
			public  XrPassthroughFlagsFB        flags;
			public  XrPassthroughLayerPurposeFB purpose;

			public XrPassthroughLayerCreateInfoFB(XrPassthroughFB passthrough, XrPassthroughFlagsFB flags, XrPassthroughLayerPurposeFB purpose)
			{
				type  = XrStructureType.XR_TYPE_PASSTHROUGH_LAYER_CREATE_INFO_FB;
				next  = IntPtr.Zero;
				this.passthrough = passthrough;
				this.flags       = flags;
				this.purpose     = purpose;
			}
		}
		[StructLayout(LayoutKind.Sequential)]
		struct XrPassthroughStyleFB
		{
			public XrStructureType             type;
			public IntPtr                      next;
			public float                       textureOpacityFactor;
			public Color                       edgeColor;
			public XrPassthroughStyleFB(float textureOpacityFactor, Color edgeColor)
			{
				type = XrStructureType.XR_TYPE_PASSTHROUGH_STYLE_FB;
				next = IntPtr.Zero;
				this.textureOpacityFactor = textureOpacityFactor;
				this.edgeColor            = edgeColor;
			}
		}
		[StructLayout(LayoutKind.Sequential)]
		struct XrCompositionLayerPassthroughFB
		{
			public XrStructureType             type;
			public IntPtr                      next;
			public XrCompositionLayerFlags     flags;
			public ulong                       space;
			public XrPassthroughLayerFB        layerHandle;
			public XrCompositionLayerPassthroughFB(XrCompositionLayerFlags flags, XrPassthroughLayerFB layerHandle)
			{
				type = XrStructureType.XR_TYPE_COMPOSITION_LAYER_PASSTHROUGH_FB;
				next = IntPtr.Zero;
				space = 0;
				this.flags = flags;
				this.layerHandle = layerHandle;
			}
		}

		delegate XrResult del_xrCreatePassthroughFB       (ulong session, [In] XrPassthroughCreateInfoFB createInfo, out XrPassthroughFB outPassthrough);
		delegate XrResult del_xrDestroyPassthroughFB      (XrPassthroughFB passthrough);
		delegate XrResult del_xrPassthroughStartFB        (XrPassthroughFB passthrough);
		delegate XrResult del_xrPassthroughPauseFB        (XrPassthroughFB passthrough);
		delegate XrResult del_xrCreatePassthroughLayerFB  (ulong session, [In] XrPassthroughLayerCreateInfoFB createInfo, out XrPassthroughLayerFB outLayer);
		delegate XrResult del_xrDestroyPassthroughLayerFB (XrPassthroughLayerFB layer);
		delegate XrResult del_xrPassthroughLayerPauseFB   (XrPassthroughLayerFB layer);
		delegate XrResult del_xrPassthroughLayerResumeFB  (XrPassthroughLayerFB layer);
		delegate XrResult del_xrPassthroughLayerSetStyleFB(XrPassthroughLayerFB layer, [In] XrPassthroughStyleFB style);

		del_xrCreatePassthroughFB        xrCreatePassthroughFB;
		del_xrDestroyPassthroughFB       xrDestroyPassthroughFB;
		del_xrPassthroughStartFB         xrPassthroughStartFB;
		del_xrPassthroughPauseFB         xrPassthroughPauseFB;
		del_xrCreatePassthroughLayerFB   xrCreatePassthroughLayerFB;
		del_xrDestroyPassthroughLayerFB  xrDestroyPassthroughLayerFB;
		del_xrPassthroughLayerPauseFB    xrPassthroughLayerPauseFB;
		del_xrPassthroughLayerResumeFB   xrPassthroughLayerResumeFB;
		del_xrPassthroughLayerSetStyleFB xrPassthroughLayerSetStyleFB;

		bool LoadBindings()
		{
			xrCreatePassthroughFB        = Backend.OpenXR.GetFunction<del_xrCreatePassthroughFB>       ("xrCreatePassthroughFB");
			xrDestroyPassthroughFB       = Backend.OpenXR.GetFunction<del_xrDestroyPassthroughFB>      ("xrDestroyPassthroughFB");
			xrPassthroughStartFB         = Backend.OpenXR.GetFunction<del_xrPassthroughStartFB>        ("xrPassthroughStartFB");
			xrPassthroughPauseFB         = Backend.OpenXR.GetFunction<del_xrPassthroughPauseFB>        ("xrPassthroughPauseFB");
			xrCreatePassthroughLayerFB   = Backend.OpenXR.GetFunction<del_xrCreatePassthroughLayerFB>  ("xrCreatePassthroughLayerFB");
			xrDestroyPassthroughLayerFB  = Backend.OpenXR.GetFunction<del_xrDestroyPassthroughLayerFB> ("xrDestroyPassthroughLayerFB");
			xrPassthroughLayerPauseFB    = Backend.OpenXR.GetFunction<del_xrPassthroughLayerPauseFB>   ("xrPassthroughLayerPauseFB");
			xrPassthroughLayerResumeFB   = Backend.OpenXR.GetFunction<del_xrPassthroughLayerResumeFB>  ("xrPassthroughLayerResumeFB");
			xrPassthroughLayerSetStyleFB = Backend.OpenXR.GetFunction<del_xrPassthroughLayerSetStyleFB>("xrPassthroughLayerSetStyleFB");

			return
				xrCreatePassthroughFB        != null &&
				xrDestroyPassthroughFB       != null &&
				xrPassthroughStartFB         != null &&
				xrPassthroughPauseFB         != null &&
				xrCreatePassthroughLayerFB   != null &&
				xrDestroyPassthroughLayerFB  != null &&
				xrPassthroughLayerPauseFB    != null &&
				xrPassthroughLayerResumeFB   != null &&
				xrPassthroughLayerSetStyleFB != null;
		}
		#endregion
	}
}