Derive gaussian splat SH order from resource layout

engine/include/XCEngine/Resources/GaussianSplat/GaussianSplat.h

@@ -43,6 +43,11 @@ enum class GaussianSplatSectionFormat : Core::uint32 {
 };
 
 constexpr Core::uint32 kGaussianSplatSHCoefficientCount = 45;
+constexpr Core::uint32 kGaussianSplatSHColorChannelCount = 3;
+constexpr Core::uint32 kGaussianSplatMaxSHOrder = 3;
+
+Core::uint32 ResolveGaussianSplatSHOrderFromCoefficientCount(Core::uint32 coefficientCount);
+Core::uint32 ResolveGaussianSplatSHOrderFromSectionStride(Core::uint32 elementStride);
 
 struct GaussianSplatPositionRecord {
     Math::Vector3 position = Math::Vector3::Zero();
@@ -113,6 +118,7 @@ public:
     GaussianSplatSectionFormat GetOtherFormat() const { return m_metadata.otherFormat; }
     GaussianSplatSectionFormat GetColorFormat() const { return m_metadata.colorFormat; }
     GaussianSplatSectionFormat GetSHFormat() const { return m_metadata.shFormat; }
+    Core::uint32 GetSHOrder() const;
     GaussianSplatSectionFormat GetChunkFormat() const { return m_metadata.chunkFormat; }
     GaussianSplatSectionFormat GetCameraFormat() const { return m_metadata.cameraFormat; }
     const Containers::Array<GaussianSplatSection>& GetSections() const { return m_sections; }

engine/src/Rendering/Passes/BuiltinGaussianSplatPass.cpp

@@ -1064,6 +1064,11 @@ bool BuiltinGaussianSplatPass::PrepareVisibleGaussianSplat(
 
     commandList->SetPipelineState(pipelineState);
 
+    const float shOrder =
+        visibleGaussianSplat.gaussianSplat != nullptr
+            ? static_cast<float>(visibleGaussianSplat.gaussianSplat->GetSHOrder())
+            : 0.0f;
+
     const PerObjectConstants perObjectConstants = {
         sceneData.cameraData.projection,
         sceneData.cameraData.view,
@@ -1080,7 +1085,7 @@ bool BuiltinGaussianSplatPass::PrepareVisibleGaussianSplat(
         Math::Vector4(
             static_cast<float>(cachedGaussianSplat->splatCount),
             static_cast<float>(workingSet->sortCapacity),
-            3.0f,
+            shOrder,
             0.0f)
     };
 

engine/src/Resources/GaussianSplat/GaussianSplat.cpp

@@ -3,6 +3,38 @@
 namespace XCEngine {
 namespace Resources {
 
+Core::uint32 ResolveGaussianSplatSHOrderFromCoefficientCount(Core::uint32 coefficientCount) {
+    if (coefficientCount == 0u || (coefficientCount % kGaussianSplatSHColorChannelCount) != 0u) {
+        return 0u;
+    }
+
+    Core::uint32 remainingTriplets = coefficientCount / kGaussianSplatSHColorChannelCount;
+    Core::uint32 resolvedOrder = 0u;
+    for (Core::uint32 order = 1u; order <= kGaussianSplatMaxSHOrder; ++order) {
+        const Core::uint32 bandTriplets = (2u * order) + 1u;
+        if (remainingTriplets < bandTriplets) {
+            break;
+        }
+
+        remainingTriplets -= bandTriplets;
+        resolvedOrder = order;
+    }
+
+    return resolvedOrder;
+}
+
+Core::uint32 ResolveGaussianSplatSHOrderFromSectionStride(Core::uint32 elementStride) {
+    if (elementStride < sizeof(float)) {
+        return 0u;
+    }
+
+    const Core::uint32 floatCount = elementStride / static_cast<Core::uint32>(sizeof(float));
+    const Core::uint32 coefficientCount = floatCount > kGaussianSplatSHCoefficientCount
+                                              ? kGaussianSplatSHCoefficientCount
+                                              : floatCount;
+    return ResolveGaussianSplatSHOrderFromCoefficientCount(coefficientCount);
+}
+
 GaussianSplat::GaussianSplat() = default;
 
 GaussianSplat::~GaussianSplat() = default;
@@ -69,6 +101,11 @@ const GaussianSplatSHRecord* GaussianSplat::GetSHRecords() const {
     return static_cast<const GaussianSplatSHRecord*>(GetSectionData(GaussianSplatSectionType::SH));
 }
 
+Core::uint32 GaussianSplat::GetSHOrder() const {
+    const GaussianSplatSection* shSection = FindSection(GaussianSplatSectionType::SH);
+    return shSection != nullptr ? ResolveGaussianSplatSHOrderFromSectionStride(shSection->elementStride) : 0u;
+}
+
 bool GaussianSplat::ValidateSections(const Containers::Array<GaussianSplatSection>& sections,
                                      size_t payloadSize) const {
     for (size_t index = 0; index < sections.Size(); ++index) {

tests/Rendering/integration/gaussian_splat_scene/main.cpp

@@ -328,6 +328,7 @@ void GaussianSplatSceneTest::PrepareRuntimeProject() {
     ASSERT_NE(m_gaussianSplat.Get(), nullptr);
     ASSERT_TRUE(m_gaussianSplat->IsValid());
     ASSERT_GT(m_gaussianSplat->GetSplatCount(), 0u);
+    ASSERT_EQ(m_gaussianSplat->GetSHOrder(), 3u);
     m_subsetGaussianSplat = CreateGaussianSplatSubset(
         *m_gaussianSplat.Get(),
         kBaselineSubsetSplatCount,
@@ -335,6 +336,7 @@ void GaussianSplatSceneTest::PrepareRuntimeProject() {
     ASSERT_NE(m_subsetGaussianSplat, nullptr);
     ASSERT_TRUE(m_subsetGaussianSplat->IsValid());
     ASSERT_GT(m_subsetGaussianSplat->GetSplatCount(), 0u);
+    ASSERT_EQ(m_subsetGaussianSplat->GetSHOrder(), 3u);
 }
 
 void GaussianSplatSceneTest::BuildScene() {

tests/Resources/GaussianSplat/test_gaussian_splat.cpp

@@ -8,6 +8,14 @@ using namespace XCEngine::Math;
 
 namespace {
 
+TEST(GaussianSplat, ResolvesSHOrderFromCoefficientCount) {
+    EXPECT_EQ(ResolveGaussianSplatSHOrderFromCoefficientCount(0u), 0u);
+    EXPECT_EQ(ResolveGaussianSplatSHOrderFromCoefficientCount(9u), 1u);
+    EXPECT_EQ(ResolveGaussianSplatSHOrderFromCoefficientCount(24u), 2u);
+    EXPECT_EQ(ResolveGaussianSplatSHOrderFromCoefficientCount(45u), 3u);
+    EXPECT_EQ(ResolveGaussianSplatSHOrderFromCoefficientCount(46u), 0u);
+}
+
 TEST(GaussianSplat, CreateOwnedStoresMetadataSectionsAndPayload) {
     GaussianSplat gaussianSplat;
 
@@ -48,6 +56,29 @@ TEST(GaussianSplat, CreateOwnedStoresMetadataSectionsAndPayload) {
     EXPECT_NE(gaussianSplat.GetSectionData(GaussianSplatSectionType::Positions), nullptr);
 }
 
+TEST(GaussianSplat, GetSHOrderUsesSHSectionStride) {
+    GaussianSplat gaussianSplat;
+
+    GaussianSplatMetadata metadata;
+    metadata.splatCount = 1u;
+
+    XCEngine::Containers::Array<GaussianSplatSection> sections;
+    sections.PushBack(GaussianSplatSection{
+        GaussianSplatSectionType::SH,
+        GaussianSplatSectionFormat::SHFloat32,
+        0u,
+        96u,
+        1u,
+        96u
+    });
+
+    XCEngine::Containers::Array<XCEngine::Core::uint8> payload;
+    payload.Resize(96u);
+
+    ASSERT_TRUE(gaussianSplat.CreateOwned(metadata, std::move(sections), std::move(payload)));
+    EXPECT_EQ(gaussianSplat.GetSHOrder(), 2u);
+}
+
 TEST(GaussianSplat, RejectsInvalidSectionLayout) {
     GaussianSplat gaussianSplat;