[UUM-117002] Fix incorrectly computed transforms and AABBs in UnifiedRayTracing API

Author: YvainRaeymaekers

Packages/com.unity.render-pipelines.core/Runtime/UnifiedRayTracing/Compute/ComputeRayTracingAccelStruct.cs

@@ -508,12 +508,15 @@ TopLevelAccelStruct CpuBuildForTopLevelAccelStruct(CommandBuffer cmd, RadeonRays
 
                 var m = ConvertTranform(instance.localToWorldTransform);
                 var bounds = GeometryUtility.CalculateBounds(new Vector3[]
-                { new Vector3(aabb.Min.x, aabb.Min.y, aabb.Max.z),
-                  new Vector3(aabb.Min.x, aabb.Max.y, aabb.Min.z),
-                  new Vector3(aabb.Min.x, aabb.Max.y, aabb.Max.z),
-                  new Vector3(aabb.Max.x, aabb.Min.y, aabb.Max.z),
-                  new Vector3(aabb.Max.x, aabb.Max.y, aabb.Min.z),
-                  new Vector3(aabb.Max.x, aabb.Max.y, aabb.Max.z)
+                {
+                    new Vector3(aabb.Min.x, aabb.Min.y, aabb.Min.z),
+                    new Vector3(aabb.Min.x, aabb.Min.y, aabb.Max.z),
+                    new Vector3(aabb.Min.x, aabb.Max.y, aabb.Min.z),
+                    new Vector3(aabb.Min.x, aabb.Max.y, aabb.Max.z),
+                    new Vector3(aabb.Max.x, aabb.Min.y, aabb.Min.z),
+                    new Vector3(aabb.Max.x, aabb.Min.y, aabb.Max.z),
+                    new Vector3(aabb.Max.x, aabb.Max.y, aabb.Min.z),
+                    new Vector3(aabb.Max.x, aabb.Max.y, aabb.Max.z)
                   }, m);
 
                 prims[i].primID = (uint)i;

Packages/com.unity.render-pipelines.core/Runtime/UnifiedRayTracing/Compute/RadeonRays/RadeonRaysAPI.cs

@@ -119,18 +119,18 @@ public static Transform TRS(float3 translation, float3 rotation, float3 scale)
 
         public Transform Inverse()
         {
-            float4x4 m = new float4x4();
-            m[0] = new float4(row0.x, row1.x, row2.x, 0);
-            m[1] = new float4(row0.y, row1.y, row2.y, 0);
-            m[2] = new float4(row0.z, row1.z, row2.z, 0);
-            m[3] = new float4(row0.w, row1.w, row2.w, 1);
+            float3x3 m = new float3x3();
+            m[0] = new float3(row0.x, row1.x, row2.x);
+            m[1] = new float3(row0.y, row1.y, row2.y);
+            m[2] = new float3(row0.z, row1.z, row2.z);
 
-            m = math.fastinverse(m);
+            m = math.inverse(m);
+            var t = -math.mul(m, new float3(row0.w, row1.w, row2.w));
 
             Transform res;
-            res.row0 = new float4(m[0].x, m[1].x, m[2].x, m[3].x);
-            res.row1 = new float4(m[0].y, m[1].y, m[2].y, m[3].y);
-            res.row2 = new float4(m[0].z, m[1].z, m[2].z, m[3].z);
+            res.row0 = new float4(m[0].x, m[1].x, m[2].x, t.x);
+            res.row1 = new float4(m[0].y, m[1].y, m[2].y, t.y);
+            res.row2 = new float4(m[0].z, m[1].z, m[2].z, t.z);
 
             return res;
         }

Packages/com.unity.render-pipelines.core/Runtime/UnifiedRayTracing/Compute/RadeonRays/kernels/transform.hlsl

@@ -66,14 +66,14 @@ Transform Inverse(in Transform t)
 
 Aabb TransformAabb(in Aabb aabb, in Transform t)
 {
-    float3 p0 = aabb.pmin;
+    float3 p0 = float3(aabb.pmin.x, aabb.pmin.y, aabb.pmin.z);
     float3 p1 = float3(aabb.pmin.x, aabb.pmin.y, aabb.pmax.z);
     float3 p2 = float3(aabb.pmin.x, aabb.pmax.y, aabb.pmin.z);
     float3 p3 = float3(aabb.pmin.x, aabb.pmax.y, aabb.pmax.z);
-    float3 p4 = float3(aabb.pmax.x, aabb.pmin.y, aabb.pmax.z);
-    float3 p5 = float3(aabb.pmax.x, aabb.pmax.y, aabb.pmin.z);
-    float3 p6 = float3(aabb.pmax.x, aabb.pmax.y, aabb.pmax.z);
-    float3 p7 = aabb.pmax;
+    float3 p4 = float3(aabb.pmax.x, aabb.pmin.y, aabb.pmin.z);
+    float3 p5 = float3(aabb.pmax.x, aabb.pmin.y, aabb.pmax.z);
+    float3 p6 = float3(aabb.pmax.x, aabb.pmax.y, aabb.pmin.z);
+    float3 p7 = float3(aabb.pmax.x, aabb.pmax.y, aabb.pmax.z);
 
     p0 = TransformPointT(p0, t);
     p1 = TransformPointT(p1, t);
@@ -98,4 +98,4 @@ Aabb TransformAabb(in Aabb aabb, in Transform t)
 }
 #endif
 
-#endif  // TRANSFORM_HLSL
+#endif  // TRANSFORM_HLSL