Enhancement: basic support for glTF LINES primitive mode

ie list of segments: wouldn't be hard to support line loops and strips I
guess, but I'd need a dataset to test that.

No support for rendering with "attenuation" like point clouds: haven't
looked at the custom vertex factory and shader yet to see how hard it
would be to support lines.

Probably need to change the name of CesiumGltfPointsComponent and proxy,
unless it makes more sense to duplicate them.

Author: GhisBntly

Source/CesiumRuntime/Private/CesiumGltfComponent.cpp

@@ -1328,6 +1328,7 @@ getIndices(const TIndexAccessor& indicesView, int32 primitiveMode) {
     break;
   case CesiumGltf::MeshPrimitive::Mode::TRIANGLES:
   case CesiumGltf::MeshPrimitive::Mode::POINTS:
+  case CesiumGltf::MeshPrimitive::Mode::LINES:
   default:
     indices.SetNum(static_cast<TArray<uint32>::SizeType>(indicesView.size()));
     for (int32 i = 0; i < indicesView.size(); ++i) {
@@ -1360,6 +1361,7 @@ static void loadPrimitive(
 
   switch (primitive.mode) {
   case CesiumGltf::MeshPrimitive::Mode::POINTS:
+  case CesiumGltf::MeshPrimitive::Mode::LINES:
   case CesiumGltf::MeshPrimitive::Mode::TRIANGLES:
   case CesiumGltf::MeshPrimitive::Mode::TRIANGLE_STRIP:
   case CesiumGltf::MeshPrimitive::Mode::TRIANGLE_FAN:
@@ -1540,8 +1542,10 @@ static void loadPrimitive(
   bool needToGenerateFlatNormals = normalsAreRequired && !hasNormals;
   bool needToGenerateTangents = needsTangents && !hasTangents;
   bool duplicateVertices = needToGenerateFlatNormals || needToGenerateTangents;
-  duplicateVertices = duplicateVertices &&
-                      primitive.mode != CesiumGltf::MeshPrimitive::Mode::POINTS;
+  duplicateVertices =
+      duplicateVertices &&
+      primitive.mode != CesiumGltf::MeshPrimitive::Mode::POINTS &&
+      primitive.mode != CesiumGltf::MeshPrimitive::Mode::LINES;
 
   uint32 numVertices =
       duplicateVertices ? uint32(indices.Num()) : uint32(positionView.size());
@@ -1759,7 +1763,8 @@ static void loadPrimitive(
   section.MinVertexIndex = 0;
   section.MaxVertexIndex = numVertices - 1;
   section.bEnableCollision =
-      primitive.mode != CesiumGltf::MeshPrimitive::Mode::POINTS;
+      primitive.mode != CesiumGltf::MeshPrimitive::Mode::POINTS &&
+      primitive.mode != CesiumGltf::MeshPrimitive::Mode::LINES;
   section.bCastShadow = true;
   section.MaterialIndex = 0;
 
@@ -1786,7 +1791,8 @@ static void loadPrimitive(
 #if ENGINE_VERSION_5_5_OR_HIGHER
   // UE 5.5 requires that we do this in order to avoid a crash when ray
   // tracing is enabled.
-  if (primitive.mode != CesiumGltf::MeshPrimitive::Mode::POINTS) {
+  if (primitive.mode != CesiumGltf::MeshPrimitive::Mode::POINTS &&
+      primitive.mode != CesiumGltf::MeshPrimitive::Mode::LINES) {
     // UE 5.5 requires that we do this in order to avoid a crash when ray
     // tracing is enabled.
     RenderData->InitializeRayTracingRepresentationFromRenderingLODs();
@@ -1800,7 +1806,7 @@ static void loadPrimitive(
 
   primitiveResult.transform = transform * yInvertMatrix * scaleMatrix;
 
-  if (primitive.mode != CesiumGltf::MeshPrimitive::Mode::POINTS &&
+  if (section.bEnableCollision &&
       options.pMeshOptions->pNodeOptions->pModelOptions->createPhysicsMeshes) {
     if (numVertices != 0 && indices.Num() != 0) {
       TRACE_CPUPROFILER_EVENT_SCOPE(Cesium::ChaosCook)
@@ -3040,9 +3046,12 @@ static void loadPrimitiveGameThreadPart(
 
   UStaticMeshComponent* pMesh = nullptr;
   ICesiumPrimitive* pCesiumPrimitive = nullptr;
-  if (meshPrimitive.mode == CesiumGltf::MeshPrimitive::Mode::POINTS) {
+  if (meshPrimitive.mode == CesiumGltf::MeshPrimitive::Mode::POINTS ||
+      meshPrimitive.mode == CesiumGltf::MeshPrimitive::Mode::LINES) {
     UCesiumGltfPointsComponent* pPointMesh =
         NewObject<UCesiumGltfPointsComponent>(pGltf, componentName);
+    pPointMesh->bLinesList =
+        (meshPrimitive.mode == CesiumGltf::MeshPrimitive::Mode::LINES);
     pPointMesh->UsesAdditiveRefinement =
         tile.getRefine() == Cesium3DTilesSelection::TileRefine::Add;
     pPointMesh->GeometricError = static_cast<float>(tile.getGeometricError());
@@ -3114,7 +3123,8 @@ static void loadPrimitiveGameThreadPart(
     // sense, but if Unreal will crash trying to generate ray tracing
     // information for a static mesh without triangles.
     pStaticMesh->bSupportRayTracing =
-        meshPrimitive.mode != CesiumGltf::MeshPrimitive::Mode::POINTS;
+        meshPrimitive.mode != CesiumGltf::MeshPrimitive::Mode::POINTS &&
+        meshPrimitive.mode != CesiumGltf::MeshPrimitive::Mode::LINES;
     pMesh->SetStaticMesh(pStaticMesh);
 
     pStaticMesh->SetFlags(

Source/CesiumRuntime/Private/CesiumGltfPointsComponent.cpp

@@ -18,7 +18,7 @@ FPrimitiveSceneProxy* UCesiumGltfPointsComponent::CreateSceneProxy() {
   }
 
   FCesiumGltfPointsSceneProxy* Proxy =
-      new FCesiumGltfPointsSceneProxy(this, GetScene()->GetFeatureLevel());
+      new FCesiumGltfPointsSceneProxy(this, GetScene()->GetFeatureLevel(), bLinesList);
 
   FCesiumGltfPointsSceneProxyTilesetData TilesetData;
   TilesetData.UpdateFromComponent(this);

Source/CesiumRuntime/Private/CesiumGltfPointsComponent.h

@@ -28,6 +28,8 @@ class UCesiumGltfPointsComponent : public UCesiumGltfPrimitiveComponent {
   // error.
   glm::vec3 Dimensions;
 
+  bool bLinesList = false;
+
   // Override UPrimitiveComponent interface.
   virtual FPrimitiveSceneProxy* CreateSceneProxy() override;
 };

Source/CesiumRuntime/Private/CesiumGltfPointsSceneProxy.cpp

@@ -26,6 +26,7 @@ void FCesiumGltfPointsSceneProxyTilesetData::UpdateFromComponent(
   UsesAdditiveRefinement = Component->UsesAdditiveRefinement;
   GeometricError = Component->GeometricError;
   Dimensions = Component->Dimensions;
+  bLinesList = Component->bLinesList;
 }
 
 SIZE_T FCesiumGltfPointsSceneProxy::GetTypeHash() const {
@@ -35,11 +36,12 @@ SIZE_T FCesiumGltfPointsSceneProxy::GetTypeHash() const {
 
 FCesiumGltfPointsSceneProxy::FCesiumGltfPointsSceneProxy(
     UCesiumGltfPointsComponent* InComponent,
-    ERHIFeatureLevel::Type InFeatureLevel)
+    ERHIFeatureLevel::Type InFeatureLevel,
+    bool bLinesList)
     : FPrimitiveSceneProxy(InComponent),
       RenderData(InComponent->GetStaticMesh()->GetRenderData()),
       NumPoints(RenderData->LODResources[0].IndexBuffer.GetNumIndices()),
-      bAttenuationSupported(
+      bAttenuationSupported(!bLinesList &&
           RHISupportsManualVertexFetch(GetScene().GetShaderPlatform())),
       TilesetData(),
       AttenuationVertexFactory(
@@ -116,6 +118,7 @@ uint32 FCesiumGltfPointsSceneProxy::GetMemoryFootprint(void) const {
 void FCesiumGltfPointsSceneProxy::UpdateTilesetData(
     const FCesiumGltfPointsSceneProxyTilesetData& InTilesetData) {
   TilesetData = InTilesetData;
+  ensure(!TilesetData.bLinesList || !bAttenuationSupported); // see ctor
 }
 
 float FCesiumGltfPointsSceneProxy::GetGeometricError() const {
@@ -208,17 +211,22 @@ void FCesiumGltfPointsSceneProxy::CreateMesh(FMeshBatch& Mesh) const {
   Mesh.VertexFactory = &RenderData->LODVertexFactories[0].VertexFactory;
   Mesh.MaterialRenderProxy = Material->GetRenderProxy();
   Mesh.ReverseCulling = IsLocalToWorldDeterminantNegative();
-  Mesh.Type = PT_PointList;
+  Mesh.Type = TilesetData.bLinesList ? PT_LineList : PT_PointList;
   Mesh.DepthPriorityGroup = SDPG_World;
   Mesh.LODIndex = 0;
   Mesh.bCanApplyViewModeOverrides = false;
   Mesh.bUseAsOccluder = false;
-  Mesh.bWireframe = false;
+  Mesh.bWireframe = TilesetData.bLinesList;
 
   FMeshBatchElement& BatchElement = Mesh.Elements[0];
   BatchElement.IndexBuffer = &RenderData->LODResources[0].IndexBuffer;
-  BatchElement.NumPrimitives = NumPoints;
   BatchElement.FirstIndex = 0;
   BatchElement.MinVertexIndex = 0;
-  BatchElement.MaxVertexIndex = BatchElement.NumPrimitives - 1;
+  BatchElement.MaxVertexIndex = NumPoints - 1;
+  if (TilesetData.bLinesList) {
+    ensure((NumPoints % 2) == 0);
+    BatchElement.NumPrimitives = NumPoints / 2;
+  } else {
+    BatchElement.NumPrimitives = NumPoints;
+  }
 }

Source/CesiumRuntime/Private/CesiumGltfPointsSceneProxy.h

@@ -19,6 +19,7 @@ struct FCesiumGltfPointsSceneProxyTilesetData {
   bool UsesAdditiveRefinement;
   float GeometricError;
   glm::vec3 Dimensions;
+  bool bLinesList;
 
   FCesiumGltfPointsSceneProxyTilesetData();
 
@@ -36,7 +37,8 @@ class FCesiumGltfPointsSceneProxy final : public FPrimitiveSceneProxy {
 
   FCesiumGltfPointsSceneProxy(
       UCesiumGltfPointsComponent* InComponent,
-      ERHIFeatureLevel::Type InFeatureLevel);
+      ERHIFeatureLevel::Type InFeatureLevel,
+      bool bLinesList);
 
   virtual ~FCesiumGltfPointsSceneProxy();