Formalize GaussianSplat scene extraction

engine/src/Rendering/Extraction/RenderSceneUtility.cpp

@@ -1,6 +1,7 @@
 #include "Rendering/Extraction/RenderSceneUtility.h"
 
 #include "Components/CameraComponent.h"
+#include "Components/GaussianSplatRendererComponent.h"
 #include "Components/GameObject.h"
 #include "Components/LightComponent.h"
 #include "Components/MeshFilterComponent.h"
@@ -175,6 +176,41 @@ void AppendVisibleVolumesForGameObject(
     outVisibleVolumes.push_back(visibleVolume);
 }
 
+void AppendVisibleGaussianSplatsForGameObject(
+    Components::GameObject& gameObject,
+    const Math::Vector3& cameraPosition,
+    std::vector<VisibleGaussianSplatItem>& outVisibleGaussianSplats) {
+    if (!gameObject.IsActiveInHierarchy()) {
+        return;
+    }
+
+    auto* gaussianSplatRenderer = gameObject.GetComponent<Components::GaussianSplatRendererComponent>();
+    if (gaussianSplatRenderer == nullptr || !gaussianSplatRenderer->IsEnabled()) {
+        return;
+    }
+
+    Resources::GaussianSplat* gaussianSplat = gaussianSplatRenderer->GetGaussianSplat();
+    Resources::Material* material = gaussianSplatRenderer->GetMaterial();
+    if (gaussianSplat == nullptr ||
+        !gaussianSplat->IsValid() ||
+        material == nullptr) {
+        return;
+    }
+
+    const Math::Matrix4x4 localToWorld = gameObject.GetTransform()->GetLocalToWorldMatrix();
+    const Math::Vector3 worldPosition = localToWorld.GetTranslation();
+
+    VisibleGaussianSplatItem visibleGaussianSplat = {};
+    visibleGaussianSplat.gameObject = &gameObject;
+    visibleGaussianSplat.gaussianSplatRenderer = gaussianSplatRenderer;
+    visibleGaussianSplat.gaussianSplat = gaussianSplat;
+    visibleGaussianSplat.material = material;
+    visibleGaussianSplat.renderQueue = ResolveMaterialRenderQueue(material);
+    visibleGaussianSplat.cameraDistanceSq = (worldPosition - cameraPosition).SqrMagnitude();
+    visibleGaussianSplat.localToWorld = localToWorld;
+    outVisibleGaussianSplats.push_back(visibleGaussianSplat);
+}
+
 bool CompareVisibleRenderItemsStable(
     const VisibleRenderItem& lhs,
     const VisibleRenderItem& rhs) {
@@ -210,6 +246,29 @@ bool CompareVisibleRenderItemsStable(
     return false;
 }
 
+bool CompareVisibleGaussianSplatsStable(
+    const VisibleGaussianSplatItem& lhs,
+    const VisibleGaussianSplatItem& rhs) {
+    if (lhs.renderQueue != rhs.renderQueue) {
+        return lhs.renderQueue < rhs.renderQueue;
+    }
+
+    const bool isTransparentQueue = IsTransparentRenderQueue(lhs.renderQueue);
+    if (lhs.cameraDistanceSq != rhs.cameraDistanceSq) {
+        return isTransparentQueue
+            ? lhs.cameraDistanceSq > rhs.cameraDistanceSq
+            : lhs.cameraDistanceSq < rhs.cameraDistanceSq;
+    }
+
+    const Core::uint64 lhsObjectId = lhs.gameObject != nullptr ? lhs.gameObject->GetID() : 0u;
+    const Core::uint64 rhsObjectId = rhs.gameObject != nullptr ? rhs.gameObject->GetID() : 0u;
+    if (lhsObjectId != rhsObjectId) {
+        return lhsObjectId < rhsObjectId;
+    }
+
+    return false;
+}
+
 bool CompareVisibleVolumesStable(
     const VisibleVolumeItem& lhs,
     const VisibleVolumeItem& rhs) {