Fix: support URP on Unity 2022 LTS

package/Runtime/GaussianSplatURPFeature.cs

@@ -1,14 +1,104 @@
 // SPDX-License-Identifier: MIT
 #if GS_ENABLE_URP
 
-#if !UNITY_6000_0_OR_NEWER
-#error Unity Gaussian Splatting URP support only works in Unity 6 or later
-#endif
-
 using UnityEngine;
 using UnityEngine.Experimental.Rendering;
 using UnityEngine.Rendering;
 using UnityEngine.Rendering.Universal;
+
+#if !UNITY_6000_0_OR_NEWER
+
+namespace GaussianSplatting.Runtime
+{
+    // Note: I have no idea what is the purpose of ScriptableRendererFeature vs ScriptableRenderPass, which one of those
+    // is supposed to do resource management vs logic, etc. etc. Code below "seems to work" but I'm just fumbling along,
+    // without understanding any of it.
+    //
+    // ReSharper disable once InconsistentNaming
+    class GaussianSplatURPFeature : ScriptableRendererFeature
+    {
+        class GSRenderPass : ScriptableRenderPass
+        {
+            RTHandle m_RenderTarget;
+            internal ScriptableRenderer m_Renderer = null;
+            internal CommandBuffer m_Cmb = null;
+
+            public void Dispose()
+            {
+                m_RenderTarget?.Release();
+            }
+
+            public override void OnCameraSetup(CommandBuffer cmd, ref RenderingData renderingData)
+            {
+                RenderTextureDescriptor rtDesc = renderingData.cameraData.cameraTargetDescriptor;
+                rtDesc.depthBufferBits = 0;
+                rtDesc.msaaSamples = 1;
+                rtDesc.graphicsFormat = GraphicsFormat.R16G16B16A16_SFloat;
+                RenderingUtils.ReAllocateIfNeeded(ref m_RenderTarget, rtDesc, FilterMode.Point, TextureWrapMode.Clamp, name: "_GaussianSplatRT");
+                cmd.SetGlobalTexture(m_RenderTarget.name, m_RenderTarget.nameID);
+
+                ConfigureTarget(m_RenderTarget, m_Renderer.cameraDepthTargetHandle);
+                ConfigureClear(ClearFlag.Color, new Color(0,0,0,0));
+            }
+
+            public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
+            {
+                if (m_Cmb == null)
+                    return;
+
+                // add sorting, view calc and drawing commands for each splat object
+                Material matComposite = GaussianSplatRenderSystem.instance.SortAndRenderSplats(renderingData.cameraData.camera, m_Cmb);
+
+                // compose
+                m_Cmb.BeginSample(GaussianSplatRenderSystem.s_ProfCompose);
+                Blitter.BlitCameraTexture(m_Cmb, m_RenderTarget, m_Renderer.cameraColorTargetHandle, RenderBufferLoadAction.Load, RenderBufferStoreAction.Store, matComposite, 0);
+                m_Cmb.EndSample(GaussianSplatRenderSystem.s_ProfCompose);
+                context.ExecuteCommandBuffer(m_Cmb);
+            }
+        }
+
+        GSRenderPass m_Pass;
+        bool m_HasCamera;
+
+        public override void Create()
+        {
+            m_Pass = new GSRenderPass
+            {
+                renderPassEvent = RenderPassEvent.BeforeRenderingTransparents
+            };
+        }
+
+        public override void OnCameraPreCull(ScriptableRenderer renderer, in CameraData cameraData)
+        {
+            m_HasCamera = false;
+            var system = GaussianSplatRenderSystem.instance;
+            if (!system.GatherSplatsForCamera(cameraData.camera))
+                return;
+
+            CommandBuffer cmb = system.InitialClearCmdBuffer(cameraData.camera);
+            m_Pass.m_Cmb = cmb;
+            m_HasCamera = true;
+        }
+
+        public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData)
+        {
+            if (!m_HasCamera)
+                return;
+            m_Pass.m_Renderer = renderer;
+            renderer.EnqueuePass(m_Pass);
+        }
+
+        protected override void Dispose(bool disposing)
+        {
+            m_Pass?.Dispose();
+            m_Pass = null;
+        }
+    }
+}
+
+
+#else
+
 using UnityEngine.Rendering.RenderGraphModule;
 
 namespace GaussianSplatting.Runtime
@@ -107,4 +197,6 @@ protected override void Dispose(bool disposing)
     }
 }
 
+#endif
+
 #endif // #if GS_ENABLE_URP