feat: add explicit camera stack ordering

engine/include/XCEngine/Components/CameraComponent.h

@@ -19,6 +19,11 @@ enum class CameraClearMode {
     None
 };
 
+enum class CameraStackType {
+    Base = 0,
+    Overlay
+};
+
 class CameraComponent : public Component {
 public:
     std::string GetName() const override { return "Camera"; }
@@ -47,6 +52,9 @@ public:
     CameraClearMode GetClearMode() const { return m_clearMode; }
     void SetClearMode(CameraClearMode value) { m_clearMode = value; }
 
+    CameraStackType GetStackType() const { return m_stackType; }
+    void SetStackType(CameraStackType value) { m_stackType = value; }
+
     uint32_t GetCullingMask() const { return m_cullingMask; }
     void SetCullingMask(uint32_t value) { m_cullingMask = value; }
 
@@ -68,6 +76,7 @@ private:
     float m_depth = 0.0f;
     bool m_primary = true;
     CameraClearMode m_clearMode = CameraClearMode::Auto;
+    CameraStackType m_stackType = CameraStackType::Base;
     uint32_t m_cullingMask = 0xFFFFFFFFu;
     Math::Rect m_viewportRect = Math::Rect(0.0f, 0.0f, 1.0f, 1.0f);
     Math::Color m_clearColor = Math::Color(0.192f, 0.302f, 0.475f, 1.0f);

engine/include/XCEngine/Rendering/CameraRenderRequest.h

@@ -19,6 +19,7 @@ struct CameraRenderRequest {
     RenderContext context;
     RenderSurface surface;
     float cameraDepth = 0.0f;
+    uint8_t cameraStackOrder = 0;
     RenderClearFlags clearFlags = RenderClearFlags::All;
     RenderPassSequence* preScenePasses = nullptr;
     RenderPassSequence* postScenePasses = nullptr;

engine/src/Components/CameraComponent.cpp

@@ -44,6 +44,7 @@ void CameraComponent::Serialize(std::ostream& os) const {
     os << "depth=" << m_depth << ";";
     os << "primary=" << (m_primary ? 1 : 0) << ";";
     os << "clearMode=" << static_cast<int>(m_clearMode) << ";";
+    os << "stackType=" << static_cast<int>(m_stackType) << ";";
     os << "cullingMask=" << m_cullingMask << ";";
     os << "viewportRect=" << m_viewportRect.x << "," << m_viewportRect.y << "," << m_viewportRect.width << "," << m_viewportRect.height << ";";
     os << "clearColor=" << m_clearColor.r << "," << m_clearColor.g << "," << m_clearColor.b << "," << m_clearColor.a << ";";
@@ -80,6 +81,8 @@ void CameraComponent::Deserialize(std::istream& is) {
             m_primary = (std::stoi(value) != 0);
         } else if (key == "clearMode") {
             m_clearMode = static_cast<CameraClearMode>(std::stoi(value));
+        } else if (key == "stackType") {
+            m_stackType = static_cast<CameraStackType>(std::stoi(value));
         } else if (key == "cullingMask") {
             m_cullingMask = static_cast<uint32_t>(std::stoul(value));
         } else if (key == "viewportRect") {

engine/src/Rendering/SceneRenderer.cpp

@@ -13,6 +13,10 @@ namespace Rendering {
 namespace {
 
 bool CompareCameraRenderRequest(const CameraRenderRequest& lhs, const CameraRenderRequest& rhs) {
+    if (lhs.cameraStackOrder != rhs.cameraStackOrder) {
+        return lhs.cameraStackOrder < rhs.cameraStackOrder;
+    }
+
     if (lhs.cameraDepth != rhs.cameraDepth) {
         return lhs.cameraDepth < rhs.cameraDepth;
     }
@@ -27,7 +31,10 @@ bool IsUsableCamera(const Components::CameraComponent* camera) {
            camera->GetGameObject()->IsActiveInHierarchy();
 }
 
-RenderClearFlags ResolveClearFlags(const Components::CameraComponent& camera, size_t cameraIndex) {
+RenderClearFlags ResolveClearFlags(
+    const Components::CameraComponent& camera,
+    size_t renderedBaseCameraCount,
+    size_t renderedRequestCount) {
     switch (camera.GetClearMode()) {
         case Components::CameraClearMode::ColorAndDepth:
             return RenderClearFlags::All;
@@ -37,7 +44,11 @@ RenderClearFlags ResolveClearFlags(const Components::CameraComponent& camera, si
             return RenderClearFlags::None;
         case Components::CameraClearMode::Auto:
         default:
-            return cameraIndex == 0 ? RenderClearFlags::All : RenderClearFlags::Depth;
+            if (camera.GetStackType() == Components::CameraStackType::Overlay) {
+                return renderedRequestCount == 0 ? RenderClearFlags::All : RenderClearFlags::Depth;
+            }
+
+            return renderedBaseCameraCount == 0 ? RenderClearFlags::All : RenderClearFlags::Depth;
     }
 }
 
@@ -101,6 +112,10 @@ std::vector<CameraRenderRequest> SceneRenderer::BuildRenderRequests(
         cameras.begin(),
         cameras.end(),
         [](const Components::CameraComponent* lhs, const Components::CameraComponent* rhs) {
+            if (lhs->GetStackType() != rhs->GetStackType()) {
+                return static_cast<int>(lhs->GetStackType()) < static_cast<int>(rhs->GetStackType());
+            }
+
             if (lhs->GetDepth() != rhs->GetDepth()) {
                 return lhs->GetDepth() < rhs->GetDepth();
             }
@@ -108,8 +123,8 @@ std::vector<CameraRenderRequest> SceneRenderer::BuildRenderRequests(
             return lhs < rhs;
         });
 
-    for (size_t cameraIndex = 0; cameraIndex < cameras.size(); ++cameraIndex) {
-        Components::CameraComponent* camera = cameras[cameraIndex];
+    size_t renderedBaseCameraCount = 0;
+    for (Components::CameraComponent* camera : cameras) {
 
         CameraRenderRequest request;
         request.scene = &scene;
@@ -118,10 +133,14 @@ std::vector<CameraRenderRequest> SceneRenderer::BuildRenderRequests(
         request.surface = surface;
         request.surface.SetRenderArea(ResolveCameraRenderArea(*camera, surface));
         request.cameraDepth = camera->GetDepth();
-        request.clearFlags = ResolveClearFlags(*camera, cameraIndex);
+        request.cameraStackOrder = static_cast<uint8_t>(camera->GetStackType());
+        request.clearFlags = ResolveClearFlags(*camera, renderedBaseCameraCount, requests.size());
         if (request.surface.GetRenderAreaWidth() > 0 &&
             request.surface.GetRenderAreaHeight() > 0) {
             requests.push_back(request);
+            if (camera->GetStackType() == Components::CameraStackType::Base) {
+                ++renderedBaseCameraCount;
+            }
         }
     }