VR support (PR #146 from ninjamode/vr-support)

- Replace projection and view-projection matrices with Unity built-ins
- Update DeviceRadixSort to an newer version that has better GPU support (needed for Quest 3)
- Uses the eye texture size in screen size calculations when available

Reportedly this makes the URP version work on Desktop Steam VR (HTC Vive), Varjo devices (Aero), Quest 3 and Quest Pro via link and standalone. Note that Apple Vision Pro is not supported due to lack of single pass instanced rendering.

package/Runtime/GaussianSplatRenderer.cs

@@ -10,6 +10,7 @@
 using UnityEngine;
 using UnityEngine.Experimental.Rendering;
 using UnityEngine.Rendering;
+using UnityEngine.XR;
 
 namespace GaussianSplatting.Runtime
 {
@@ -301,9 +302,7 @@ internal static class Props
             public static readonly int SrcBuffer = Shader.PropertyToID("_SrcBuffer");
             public static readonly int DstBuffer = Shader.PropertyToID("_DstBuffer");
             public static readonly int BufferSize = Shader.PropertyToID("_BufferSize");
-            public static readonly int MatrixVP = Shader.PropertyToID("_MatrixVP");
             public static readonly int MatrixMV = Shader.PropertyToID("_MatrixMV");
-            public static readonly int MatrixP = Shader.PropertyToID("_MatrixP");
             public static readonly int MatrixObjectToWorld = Shader.PropertyToID("_MatrixObjectToWorld");
             public static readonly int MatrixWorldToObject = Shader.PropertyToID("_MatrixWorldToObject");
             public static readonly int VecScreenParams = Shader.PropertyToID("_VecScreenParams");
@@ -552,15 +551,14 @@ internal void CalcViewData(CommandBuffer cmb, Camera cam, Matrix4x4 matrix)
             Matrix4x4 matO2W = tr.localToWorldMatrix;
             Matrix4x4 matW2O = tr.worldToLocalMatrix;
             int screenW = cam.pixelWidth, screenH = cam.pixelHeight;
-            Vector4 screenPar = new Vector4(screenW, screenH, 0, 0);
+            int eyeW = XRSettings.eyeTextureWidth, eyeH = XRSettings.eyeTextureHeight;
+            Vector4 screenPar = new Vector4(eyeW != 0 ? eyeW : screenW, eyeH != 0 ? eyeH : screenH, 0, 0);
             Vector4 camPos = cam.transform.position;
 
             // calculate view dependent data for each splat
             SetAssetDataOnCS(cmb, KernelIndices.CalcViewData);
 
-            cmb.SetComputeMatrixParam(m_CSSplatUtilities, Props.MatrixVP, matProj * matView);
             cmb.SetComputeMatrixParam(m_CSSplatUtilities, Props.MatrixMV, matView * matO2W);
-            cmb.SetComputeMatrixParam(m_CSSplatUtilities, Props.MatrixP, matProj);
             cmb.SetComputeMatrixParam(m_CSSplatUtilities, Props.MatrixObjectToWorld, matO2W);
             cmb.SetComputeMatrixParam(m_CSSplatUtilities, Props.MatrixWorldToObject, matW2O);
 
@@ -784,9 +782,7 @@ public void EditUpdateSelection(Vector2 rectMin, Vector2 rectMax, Camera cam, bo
             using var cmb = new CommandBuffer { name = "SplatSelectionUpdate" };
             SetAssetDataOnCS(cmb, KernelIndices.SelectionUpdate);
 
-            cmb.SetComputeMatrixParam(m_CSSplatUtilities, Props.MatrixVP, matProj * matView);
             cmb.SetComputeMatrixParam(m_CSSplatUtilities, Props.MatrixMV, matView * matO2W);
-            cmb.SetComputeMatrixParam(m_CSSplatUtilities, Props.MatrixP, matProj);
             cmb.SetComputeMatrixParam(m_CSSplatUtilities, Props.MatrixObjectToWorld, matO2W);
             cmb.SetComputeMatrixParam(m_CSSplatUtilities, Props.MatrixWorldToObject, matW2O);
 

package/Runtime/GpuSorting.cs

@@ -5,7 +5,7 @@
 namespace GaussianSplatting.Runtime
 {
     // GPU (uint key, uint payload) 8 bit-LSD radix sort, using reduce-then-scan
-    // Copyright Thomas Smith 2023, MIT license
+    // Copyright Thomas Smith 2024, MIT license
     // https://github.com/b0nes164/GPUSorting
 
     public class GpuSorting
@@ -22,6 +22,13 @@ public class GpuSorting
         //Number of sorting passes required to sort a 32bit key, KEY_BITS / DEVICE_RADIX_SORT_BITS
         const uint DEVICE_RADIX_SORT_PASSES = 4;
 
+        //Keywords to enable for the shader
+        private LocalKeyword m_keyUintKeyword;
+        private LocalKeyword m_payloadUintKeyword;
+        private LocalKeyword m_ascendKeyword;
+        private LocalKeyword m_sortPairKeyword;
+        private LocalKeyword m_vulkanKeyword;
+
         public struct Args
         {
             public uint             count;
@@ -104,6 +111,21 @@ public GpuSorting(ComputeShader cs)
                     m_Valid = false;
                 }
             }
+
+            m_keyUintKeyword = new LocalKeyword(cs, "KEY_UINT");
+            m_payloadUintKeyword = new LocalKeyword(cs, "PAYLOAD_UINT");
+            m_ascendKeyword = new LocalKeyword(cs, "SHOULD_ASCEND");
+            m_sortPairKeyword = new LocalKeyword(cs, "SORT_PAIRS");
+            m_vulkanKeyword = new LocalKeyword(cs, "VULKAN");
+
+            cs.EnableKeyword(m_keyUintKeyword);
+            cs.EnableKeyword(m_payloadUintKeyword);
+            cs.EnableKeyword(m_ascendKeyword);
+            cs.EnableKeyword(m_sortPairKeyword);
+            if (SystemInfo.graphicsDeviceType == UnityEngine.Rendering.GraphicsDeviceType.Vulkan)
+                cs.EnableKeyword(m_vulkanKeyword);
+            else
+                cs.DisableKeyword(m_vulkanKeyword);
         }
 
         static uint DivRoundUp(uint x, uint y) => (x + y - 1) / y;