From 0a0544cbe4743e36922ae44b2c69fbd6844b11aa Mon Sep 17 00:00:00 2001
From: ssdfasd <2156608475@qq.com>
Date: Wed, 1 Apr 2026 22:28:07 +0800
Subject: [PATCH] fix: compose camera viewport within parent render area

---
 engine/src/Rendering/SceneRenderer.cpp        | 17 ++++---
 .../unit/test_camera_scene_renderer.cpp       | 48 +++++++++++++++++++
 2 files changed, 59 insertions(+), 6 deletions(-)

diff --git a/engine/src/Rendering/SceneRenderer.cpp b/engine/src/Rendering/SceneRenderer.cpp
index b2af9df8..b4e44bc8 100644
--- a/engine/src/Rendering/SceneRenderer.cpp
+++ b/engine/src/Rendering/SceneRenderer.cpp
@@ -56,13 +56,18 @@ Math::RectInt ResolveCameraRenderArea(
     const Components::CameraComponent& camera,
     const RenderSurface& surface) {
     const Math::Rect viewportRect = camera.GetViewportRect();
-    const float surfaceWidth = static_cast<float>(surface.GetWidth());
-    const float surfaceHeight = static_cast<float>(surface.GetHeight());
+    const Math::RectInt parentRenderArea = surface.GetRenderArea();
+    const float parentWidth = static_cast<float>(std::max(parentRenderArea.width, 0));
+    const float parentHeight = static_cast<float>(std::max(parentRenderArea.height, 0));
 
-    const int32_t left = static_cast<int32_t>(std::floor(viewportRect.x * surfaceWidth));
-    const int32_t top = static_cast<int32_t>(std::floor(viewportRect.y * surfaceHeight));
-    const int32_t right = static_cast<int32_t>(std::ceil((viewportRect.x + viewportRect.width) * surfaceWidth));
-    const int32_t bottom = static_cast<int32_t>(std::ceil((viewportRect.y + viewportRect.height) * surfaceHeight));
+    const int32_t left = parentRenderArea.x +
+        static_cast<int32_t>(std::floor(viewportRect.x * parentWidth));
+    const int32_t top = parentRenderArea.y +
+        static_cast<int32_t>(std::floor(viewportRect.y * parentHeight));
+    const int32_t right = parentRenderArea.x +
+        static_cast<int32_t>(std::ceil((viewportRect.x + viewportRect.width) * parentWidth));
+    const int32_t bottom = parentRenderArea.y +
+        static_cast<int32_t>(std::ceil((viewportRect.y + viewportRect.height) * parentHeight));
     return Math::RectInt(left, top, right - left, bottom - top);
 }
 
diff --git a/tests/Rendering/unit/test_camera_scene_renderer.cpp b/tests/Rendering/unit/test_camera_scene_renderer.cpp
index e64085ad..404a7fa7 100644
--- a/tests/Rendering/unit/test_camera_scene_renderer.cpp
+++ b/tests/Rendering/unit/test_camera_scene_renderer.cpp
@@ -537,6 +537,54 @@ TEST(SceneRenderer_Test, ResolvesNormalizedCameraViewportRectToPerRequestRenderA
     EXPECT_EQ(renderArea.height, 240);
 }
 
+TEST(SceneRenderer_Test, ComposesCameraViewportRectWithinExistingSurfaceRenderArea) {
+    Scene scene("SceneRendererNestedViewportRectScene");
+
+    GameObject* cameraObject = scene.CreateGameObject("Camera");
+    auto* camera = cameraObject->AddComponent<CameraComponent>();
+    camera->SetPrimary(true);
+    camera->SetDepth(2.0f);
+    camera->SetViewportRect(XCEngine::Math::Rect(0.25f, 0.1f, 0.5f, 0.4f));
+
+    RenderSurface surface(800, 600);
+    surface.SetRenderArea(XCEngine::Math::RectInt(100, 50, 400, 300));
+
+    SceneRenderer renderer;
+    const std::vector<CameraRenderRequest> requests =
+        renderer.BuildRenderRequests(scene, nullptr, CreateValidContext(), surface);
+
+    ASSERT_EQ(requests.size(), 1u);
+    const XCEngine::Math::RectInt renderArea = requests[0].surface.GetRenderArea();
+    EXPECT_EQ(renderArea.x, 200);
+    EXPECT_EQ(renderArea.y, 80);
+    EXPECT_EQ(renderArea.width, 200);
+    EXPECT_EQ(renderArea.height, 120);
+}
+
+TEST(SceneRenderer_Test, PreservesExistingSurfaceRenderAreaForFullViewportCamera) {
+    Scene scene("SceneRendererFullViewportNestedSurfaceScene");
+
+    GameObject* cameraObject = scene.CreateGameObject("Camera");
+    auto* camera = cameraObject->AddComponent<CameraComponent>();
+    camera->SetPrimary(true);
+    camera->SetDepth(2.0f);
+    camera->SetViewportRect(XCEngine::Math::Rect(0.0f, 0.0f, 1.0f, 1.0f));
+
+    RenderSurface surface(1024, 768);
+    surface.SetRenderArea(XCEngine::Math::RectInt(80, 120, 320, 240));
+
+    SceneRenderer renderer;
+    const std::vector<CameraRenderRequest> requests =
+        renderer.BuildRenderRequests(scene, nullptr, CreateValidContext(), surface);
+
+    ASSERT_EQ(requests.size(), 1u);
+    const XCEngine::Math::RectInt renderArea = requests[0].surface.GetRenderArea();
+    EXPECT_EQ(renderArea.x, 80);
+    EXPECT_EQ(renderArea.y, 120);
+    EXPECT_EQ(renderArea.width, 320);
+    EXPECT_EQ(renderArea.height, 240);
+}
+
 TEST(CameraRenderer_Test, UsesResolvedRenderAreaForCameraViewportDimensions) {
     Scene scene("CameraRendererViewportRectScene");