Added the DoubleSidedCollisions property to the ACesium3DTileset actors

CHANGES.md

@@ -1,5 +1,11 @@
 # Change Log {#changes}
 
+### v?.??.? - ????-??-??
+
+##### Additions :tada:
+
+- Added the `DoubleSidedCollisions` boolean property to the `ACesium3DTileset` actor, allowing intersections and collisions with geometry to also work when hitting "back" faces.
+
 ### v2.21.0 - 2025-11-03
 
 ##### Additions :tada:

Source/CesiumRuntime/Private/Cesium3DTileset.cpp

@@ -492,6 +492,13 @@ void ACesium3DTileset::SetCreatePhysicsMeshes(bool bCreatePhysicsMeshes) {
   }
 }
 
+void ACesium3DTileset::SetDoubleSidedCollisions(bool bDoubleSidedCollisions) {
+  if (this->DoubleSidedCollisions != bDoubleSidedCollisions) {
+    this->DoubleSidedCollisions = bDoubleSidedCollisions;
+    this->DestroyTileset();
+  }
+}
+
 void ACesium3DTileset::SetCreateNavCollision(bool bCreateNavCollision) {
   if (this->CreateNavCollision != bCreateNavCollision) {
     this->CreateNavCollision = bCreateNavCollision;

Source/CesiumRuntime/Private/CesiumGltfComponent.cpp

@@ -3021,6 +3021,7 @@ static void loadPrimitiveGameThreadPart(
     const glm::dmat4x4& cesiumToUnrealTransform,
     const Cesium3DTilesSelection::Tile& tile,
     bool createNavCollision,
+    bool doubleSidedCollisions,
     ACesium3DTileset* pTilesetActor,
     const std::vector<FTransform>& instanceTransforms,
     const TSharedPtr<FCesiumPrimitiveFeatures>& pInstanceFeatures) {
@@ -3431,6 +3432,7 @@ static void loadPrimitiveGameThreadPart(
         ECollisionTraceFlag::CTF_UseComplexAsSimple;
 
     if (loadResult.pCollisionMesh) {
+      pBodySetup->bDoubleSidedGeometry = doubleSidedCollisions;
       pBodySetup->TriMeshGeometries.Add(loadResult.pCollisionMesh);
     }
 
@@ -3485,7 +3487,8 @@ UCesiumGltfComponent::CreateOffGameThread(
     UMaterialInterface* pBaseWaterMaterial,
     FCustomDepthParameters CustomDepthParameters,
     const Cesium3DTilesSelection::Tile& tile,
-    bool createNavCollision) {
+    bool createNavCollision,
+    bool doubleSidedCollisions) {
   TRACE_CPUPROFILER_EVENT_SCOPE(Cesium::LoadModel)
 
   HalfConstructedReal* pReal =
@@ -3538,6 +3541,7 @@ UCesiumGltfComponent::CreateOffGameThread(
             cesiumToUnrealTransform,
             tile,
             createNavCollision,
+            doubleSidedCollisions,
             pTilesetActor,
             node.InstanceTransforms,
             node.pInstanceFeatures);
@@ -3883,5 +3887,11 @@ static Chaos::FTriangleMeshImplicitObjectPtr BuildChaosTriangleMeshes(
       MoveTemp(materials),
       MoveTemp(pFaceRemap),
       nullptr,
-      false);
+      // Not sure what this is for: in my experience, whatever you pass here is
+      // overridden later on by a call to SetCullsBackFaceRaycast (from
+      // RegisterComponent) which will reset the property depending on the value
+      // of UBodySetup::bDoubleSidedGeometry.
+      // See ACesium3DTileset::DoubleSidedCollisions to effectively enable
+      // backface hits.
+      /*bInCullsBackFaceRaycast*/false);
 }

Source/CesiumRuntime/Private/CesiumGltfComponent.h

@@ -90,7 +90,8 @@ class UCesiumGltfComponent : public USceneComponent, public ICesiumLoadedTile {
       UMaterialInterface* BaseWaterMaterial,
       FCustomDepthParameters CustomDepthParameters,
       const Cesium3DTilesSelection::Tile& tile,
-      bool createNavCollision);
+      bool createNavCollision,
+      bool doubleSidedCollisions);
 
   UCesiumGltfComponent();
 

Source/CesiumRuntime/Private/UnrealPrepareRendererResources.cpp

@@ -85,7 +85,8 @@ void* UnrealPrepareRendererResources::prepareInMainThread(
         this->_pActor->GetWaterMaterial(),
         this->_pActor->GetCustomDepthParameters(),
         tile,
-        this->_pActor->GetCreateNavCollision());
+        this->_pActor->GetCreateNavCollision(),
+        this->_pActor->GetDoubleSidedCollisions());
   }
   // UE_LOG(LogCesium, VeryVerbose, TEXT("No content for tile"));
   return nullptr;

Source/CesiumRuntime/Public/Cesium3DTileset.h

@@ -799,6 +799,17 @@ class CESIUMRUNTIME_API ACesium3DTileset : public AActor {
       Category = "Cesium|Physics")
   bool CreatePhysicsMeshes = true;
 
+  /**
+   * Whether to enable doubled-sided collisions (both "front" and "back" faces)
+   * on the physics meshes created when CreatePhysicsMeshes is true.
+   */
+  UPROPERTY(
+      EditAnywhere,
+      BlueprintGetter = GetDoubleSidedCollisions,
+      BlueprintSetter = SetDoubleSidedCollisions,
+      Category = "Cesium|Physics")
+  bool DoubleSidedCollisions = false;
+
   /**
    * Whether to generate navigation collisions for this tileset.
    *
@@ -1095,6 +1106,12 @@ class CESIUMRUNTIME_API ACesium3DTileset : public AActor {
   UFUNCTION(BlueprintSetter, Category = "Cesium|Physics")
   void SetCreatePhysicsMeshes(bool bCreatePhysicsMeshes);
 
+  UFUNCTION(BlueprintGetter, Category = "Cesium|Physics")
+  bool GetDoubleSidedCollisions() const { return DoubleSidedCollisions; }
+
+  UFUNCTION(BlueprintSetter, Category = "Cesium|Physics")
+  void SetDoubleSidedCollisions(bool bCreatePhysicsMeshes);
+
   UFUNCTION(BlueprintGetter, Category = "Cesium|Navigation")
   bool GetCreateNavCollision() const { return CreateNavCollision; }