More changes

editor/main.cpp

@@ -21,16 +21,15 @@ class Editor : public sophia::Application {
 
     sophia::SceneHandle sceneHandle = scenes().create();
     sophia::Scene& scene = scenes().get(sceneHandle);
-    sophia::Entity camera = createDemoScene(scene);
+    createDemoScene(scene);
 
     panels().emplace<SceneHierarchyPanel>(scene, selected);
     panels().emplace<InspectorPanel>(selected, textures);
     panels().emplace<AssetBrowserPanel>();
     sophia::RenderTargetHandle sceneTarget =
         resources().create<sophia::RenderTarget>();
-    views().create(
-        {.scene = sceneHandle, .target = sceneTarget, .camera = camera});
-    panels().emplace<ViewportPanel>(ui(), sceneTarget);
+    views().create({.scene = sceneHandle, .target = sceneTarget});
+    panels().emplace<ViewportPanel>(ui(), sceneTarget, scene, selected);
 
     panels().setDefaultLayout(
         {.left = {"Scene Hierarchy"},
@@ -42,10 +41,8 @@ class Editor : public sophia::Application {
   void onUpdate(const sophia::FrameInfo& frameInfo) override {}
 
  private:
-  sophia::Entity createDemoScene(sophia::Scene& scene) {
-    sophia::Entity camera = scene.createEntity("Main Camera");
-    camera.addComponent<sophia::CameraComponent>();
-    scene.setActiveCamera(camera);
+  void createDemoScene(sophia::Scene& scene) {
+    scene.createCamera("Main Camera");
 
     sophia::Entity checker = scene.createEntity("Checker");
     checker.getComponent<sophia::TransformComponent>().position = {-1.5f, 0.f,
@@ -66,8 +63,6 @@ class Editor : public sophia::Application {
         sophia::SpriteComponent{.color = {0.25f, 0.45f, 0.95f, 0.6f},
                                 .size = {2.f, 2.f},
                                 .sortOrder = 1});
-
-    return camera;
   }
 
   sophia::TextureHandle createCheckerTexture() {

editor/panels/viewport_panel.cpp

@@ -2,7 +2,86 @@
 
 #include <imgui.h>
 
+#include <array>
+#include <optional>
+#include <sophia/components.hpp>
+#include <tuple>
+
+namespace {
+
+// Corners of the unit quad a SpriteComponent's model matrix maps to world.
+constexpr std::array<glm::vec2, 4> UNIT_QUAD{
+    glm::vec2{0.f, 0.f}, glm::vec2{1.f, 0.f}, glm::vec2{1.f, 1.f},
+    glm::vec2{0.f, 1.f}};
+
+const ImU32 SELECTION_COLOR = IM_COL32(255, 170, 40, 255);
+
+}  // namespace
+
+ImVec2 ViewportPanel::ViewportTransform::worldToScreen(
+    const glm::vec3& world) const {
+  glm::vec4 clip = viewProjection * glm::vec4{world, 1.f};
+  glm::vec2 ndc = glm::vec2{clip} / clip.w;
+  // Vulkan NDC has +y pointing down, same as the screen.
+  return {origin.x + (ndc.x * 0.5f + 0.5f) * size.x,
+          origin.y + (ndc.y * 0.5f + 0.5f) * size.y};
+}
+
+glm::vec2 ViewportPanel::ViewportTransform::screenToWorld(
+    const ImVec2& screen) const {
+  glm::vec2 ndc{(screen.x - origin.x) / size.x * 2.f - 1.f,
+                (screen.y - origin.y) / size.y * 2.f - 1.f};
+  glm::vec4 world = inverseViewProjection * glm::vec4{ndc, 0.f, 1.f};
+  return glm::vec2{world} / world.w;
+}
+
 void ViewportPanel::onUpdate(const sophia::FrameInfo&) {
+  drawToolbar();
+  ImGui::Separator();
+
+  const ImVec2 origin = ImGui::GetCursorScreenPos();
+  const ImVec2 size = ImGui::GetContentRegionAvail();
+  if (size.x < 1.0f || size.y < 1.0f) {
+    return;
+  }
+
+  ui.image(target);
+
+  // The image doesn't take mouse input, so without this, dragging in it
+  // would drag the window instead.
+  ImGui::SetCursorScreenPos(origin);
+  ImGui::InvisibleButton("##viewport", size);
+
+  ImDrawList* drawList = ImGui::GetWindowDrawList();
+  drawList->PushClipRect(origin, ImVec2(origin.x + size.x, origin.y + size.y),
+                         true);
+
+  if (showGrid) {
+    drawGrid(origin, size);
+  }
+
+  sophia::Entity camera = scene.getActiveCamera();
+  if (camera && camera.hasComponent<sophia::CameraComponent>()) {
+    // Use the panel's size rather than the target's: the target is resized
+    // a frame late, and the mouse is over the panel.
+    float aspect = size.x / size.y;
+    glm::mat4 viewProjection =
+        camera.getComponent<sophia::CameraComponent>().getViewProjection(
+            camera.getComponent<sophia::TransformComponent>(), aspect);
+
+    ViewportTransform viewport{origin, size, viewProjection,
+                               glm::inverse(viewProjection)};
+    handleInput(viewport);
+    drawSelection(viewport);
+  }
+
+  drawList->PopClipRect();
+
+  ImGui::SetCursorScreenPos(ImVec2(origin.x + 8.0f, origin.y + 8.0f));
+  ImGui::TextDisabled("%.0f x %.0f", size.x, size.y);
+}
+
+void ViewportPanel::drawToolbar() {
   const struct {
     const char* label;
     GizmoMode mode;
@@ -17,20 +96,14 @@ void ViewportPanel::onUpdate(const sophia::FrameInfo&) {
     ImGui::SameLine();
   }
   ImGui::Checkbox("Grid", &showGrid);
+}
 
-  ImGui::Separator();
-
-  const ImVec2 origin = ImGui::GetCursorScreenPos();
-  const ImVec2 size = ImGui::GetContentRegionAvail();
-  const ImVec2 end(origin.x + size.x, origin.y + size.y);
-
-  ui.image(target);
-
-  ImDrawList* drawList = ImGui::GetWindowDrawList();
-
-  if (showGrid) {
+void ViewportPanel::drawGrid(ImVec2 origin, ImVec2 size) {
   constexpr float GRID_STEP = 40.0f;
   const ImU32 gridColor = IM_COL32(255, 255, 255, 18);
+  const ImVec2 end(origin.x + size.x, origin.y + size.y);
+
+  ImDrawList* drawList = ImGui::GetWindowDrawList();
   for (float x = GRID_STEP; x < size.x; x += GRID_STEP) {
     drawList->AddLine(ImVec2(origin.x + x, origin.y),
                       ImVec2(origin.x + x, end.y), gridColor);
@@ -41,6 +114,89 @@ void ViewportPanel::onUpdate(const sophia::FrameInfo&) {
   }
 }
 
-  ImGui::SetCursorScreenPos(ImVec2(origin.x + 8.0f, origin.y + 8.0f));
-  ImGui::TextDisabled("%.0f x %.0f", size.x, size.y);
+void ViewportPanel::handleInput(const ViewportTransform& viewport) {
+  const ImGuiIO& io = ImGui::GetIO();
+
+  if (ImGui::IsItemActivated()) {
+    selected = pick(viewport.screenToWorld(io.MousePos));
+    dragging = selected && gizmoMode == GizmoMode::Move;
+  }
+
+  if (!ImGui::IsItemActive()) {
+    dragging = false;
+    return;
+  }
+
+  if (dragging && (io.MouseDelta.x != 0.f || io.MouseDelta.y != 0.f)) {
+    ImVec2 previous(io.MousePos.x - io.MouseDelta.x,
+                    io.MousePos.y - io.MouseDelta.y);
+    glm::vec2 delta =
+        viewport.screenToWorld(io.MousePos) - viewport.screenToWorld(previous);
+
+    auto& transform = selected.getComponent<sophia::TransformComponent>();
+    transform.position.x += delta.x;
+    transform.position.y += delta.y;
+  }
+}
+
+void ViewportPanel::drawSelection(const ViewportTransform& viewport) {
+  if (!selected) {
+    return;
+  }
+
+  ImDrawList* drawList = ImGui::GetWindowDrawList();
+  const auto& transform = selected.getComponent<sophia::TransformComponent>();
+
+  if (selected.hasComponent<sophia::SpriteComponent>()) {
+    glm::mat4 model =
+        selected.getComponent<sophia::SpriteComponent>().getModel(transform);
+
+    std::array<ImVec2, 4> corners;
+    for (size_t i = 0; i < UNIT_QUAD.size(); i++) {
+      corners[i] = viewport.worldToScreen(
+          glm::vec3{model * glm::vec4{UNIT_QUAD[i], 0.f, 1.f}});
+    }
+    drawList->AddQuad(corners[0], corners[1], corners[2], corners[3],
+                      SELECTION_COLOR, 2.0f);
+  }
+
+  // Mark the transform's position (the sprite's pivot), which is also all
+  // there is to show for entities without a sprite, such as the camera.
+  ImVec2 center = viewport.worldToScreen(transform.position);
+  drawList->AddCircle(center, 4.0f, SELECTION_COLOR, 0, 2.0f);
+}
+
+sophia::Entity ViewportPanel::pick(glm::vec2 world) {
+  sophia::Entity best;
+  std::optional<std::tuple<sophia::s32, float>> bestOrder;
+
+  scene.forEachEntity([&](sophia::Entity entity) {
+    if (!entity.hasComponent<sophia::SpriteComponent>()) {
+      return;
+    }
+
+    const auto& transform = entity.getComponent<sophia::TransformComponent>();
+    const auto& sprite = entity.getComponent<sophia::SpriteComponent>();
+
+    glm::mat4 model = sprite.getModel(transform);
+    // Zero size or scale; nothing to hit.
+    if (glm::determinant(model) == 0.f) {
+      return;
+    }
+
+    glm::vec4 local =
+        glm::inverse(model) * glm::vec4{world, transform.position.z, 1.f};
+    if (local.x < 0.f || local.x > 1.f || local.y < 0.f || local.y > 1.f) {
+      return;
+    }
+
+    // Same ordering the renderer draws in, so this is the one on top.
+    std::tuple order{sprite.sortOrder, transform.position.z};
+    if (!bestOrder || order >= *bestOrder) {
+      best = entity;
+      bestOrder = order;
+    }
+  });
+
+  return best;
 }

editor/panels/viewport_panel.hpp

@@ -1,27 +1,64 @@
 #pragma once
 
+#include <sophia/entity.hpp>
 #include <sophia/frame_info.hpp>
 #include <sophia/handles.hpp>
+#include <sophia/math.hpp>
+#include <sophia/scene.hpp>
 #include <sophia/ui/panel.hpp>
 #include <sophia/ui/ui.hpp>
 
+/**
+ * Shows the scene through its active camera. Click a sprite to select it,
+ * drag it to move it (in Move mode).
+ *
+ * Picking and moving are 2D: they assume an orthographic camera rotated only
+ * around Z, and work in the z = 0 plane.
+ */
 class ViewportPanel : public sophia::Panel {
  public:
-  ViewportPanel(sophia::UI& ui, sophia::RenderTargetHandle target)
+  ViewportPanel(sophia::UI& ui, sophia::RenderTargetHandle target,
+                sophia::Scene& scene, sophia::Entity& selected)
       : Panel{{.name = "Viewport",
                .windowFlags = ImGuiWindowFlags_NoScrollbar |
                               ImGuiWindowFlags_NoScrollWithMouse}},
         ui{ui},
-        target{target} {}
+        target{target},
+        scene{scene},
+        selected{selected} {}
 
   void onUpdate(const sophia::FrameInfo& frameInfo) override;
 
  private:
+  // Where the scene image is on screen this frame, and the camera looking
+  // through it.
+  struct ViewportTransform {
+    ImVec2 origin;
+    ImVec2 size;
+    glm::mat4 viewProjection;
+    glm::mat4 inverseViewProjection;
+
+    ImVec2 worldToScreen(const glm::vec3& world) const;
+    glm::vec2 screenToWorld(const ImVec2& screen) const;
+  };
+
+  void drawToolbar();
+  void drawGrid(ImVec2 origin, ImVec2 size);
+  void handleInput(const ViewportTransform& viewport);
+  void drawSelection(const ViewportTransform& viewport);
+
+  // The top-most sprite under `world`, or a null Entity.
+  sophia::Entity pick(glm::vec2 world);
+
   sophia::UI& ui;
   sophia::RenderTargetHandle target;
+  sophia::Scene& scene;
+  sophia::Entity& selected;
 
   enum class GizmoMode { Move, Rotate, Scale };
 
   GizmoMode gizmoMode = GizmoMode::Move;
   bool showGrid = true;
+  // Set while a drag that started on the selected entity is moving it.
+  bool dragging = false;
 };

engine/include/sophia/components.hpp

@@ -66,6 +66,14 @@ struct SpriteComponent {
 
   // Higher draws on top. Ties are broken by the transform's position.z.
   s32 sortOrder = 0;
+
+  // Maps the unit quad (0, 0)-(1, 1) to world space: to the sprite's
+  // rectangle around its pivot, then by `transform`.
+  glm::mat4 getModel(const TransformComponent& transform) const {
+    return transform.mat4() *
+           glm::translate(glm::mat4{1.f}, glm::vec3{-pivot * size, 0.f}) *
+           glm::scale(glm::mat4{1.f}, glm::vec3{size, 1.f});
+  }
 };
 
 struct CameraComponent {
@@ -98,6 +106,15 @@ struct CameraComponent {
     return glm::ortho(-halfWidth, halfWidth, -halfHeight, halfHeight,
                       ortho.nearPlane, ortho.farPlane);
   }
+
+  // World -> clip space for this camera placed by `transform`. The view
+  // ignores the transform's scale; zoom is the projection's job.
+  glm::mat4 getViewProjection(const TransformComponent& transform,
+                              float aspect) const {
+    glm::mat4 world = glm::translate(glm::mat4{1.f}, transform.position) *
+                      glm::mat4_cast(transform.rotation);
+    return getProjection(aspect) * glm::inverse(world);
+  }
 };
 
 }  // namespace sophia

engine/include/sophia/scene.hpp

@@ -13,18 +13,17 @@ class Scene {
   Scene();
   ~Scene();
 
-  // Every entity gets a TagComponent (named `name`) and a TransformComponent.
   Entity createEntity(const std::string& name = {});
   void destroyEntity(Entity entity);
 
+  Entity createCamera(const std::string& name = "Camera");
+
   /** Calls `fn(Entity)` for every live entity. Defined in entity.hpp. */
   template <typename Fn>
   void forEachEntity(Fn&& fn);
 
-  // The camera a render request uses when it doesn't name one. Null until
-  // set.
-  entt::entity getActiveCamera() const { return activeCamera; }
-  void setActiveCamera(entt::entity camera) { activeCamera = camera; }
+  Entity getActiveCamera();
+  void setActiveCamera(Entity camera);
 
  private:
   friend class Entity;

engine/include/sophia/scene_registry.hpp

@@ -19,6 +19,8 @@ class SceneRegistry {
   const Scene& get(SceneHandle handle) const { return pool.get(handle); }
   Scene& get(SceneHandle handle) { return pool.get(handle); }
 
+  const Scene& peek(SceneHandle handle) const { return pool.get(handle); }
+
   void release(SceneHandle handle) { pool.release(handle); }
   bool isAlive(SceneHandle handle) const { return pool.isAlive(handle); }
 

engine/include/sophia/scene_view.hpp

@@ -17,8 +17,9 @@ enum class ClearFlags : u8 {
 
 struct SceneView {
   SceneHandle scene = INVALID_HANDLE;
-  RenderTargetHandle target = INVALID_HANDLE;
-  Entity camera;
+  RenderTargetHandle target =
+      INVALID_HANDLE;  // null implies render to swapchain
+  Entity camera;       // null implies use scene's active camera
 
   vec4 viewport{0.0f, 0.0f, 1.0f, 1.0f};
 

engine/include/sophia/scene_view_registry.hpp

@@ -35,6 +35,10 @@ class SceneViewRegistry {
     return pool.get(handle);
   }
 
+  const SceneView& peek(SceneViewHandle handle) const {
+    return pool.get(handle);
+  }
+
   void release(SceneViewHandle handle) {
     isRenderQueueDirty = true;
     pool.release(handle);

engine/src/application.cpp

@@ -6,6 +6,7 @@
 #include <cstddef>
 #include <glm/glm.hpp>
 #include <map>
+#include <set>
 #include <sophia/application.hpp>
 #include <sophia/util/logger.hpp>
 #include <string>
@@ -87,11 +88,12 @@ class Application::Impl {
     PanelRegistry& panelRegistry = this->application.panelRegistry;
     SceneRegistry& sceneRegistry = this->application.sceneRegistry;
     SceneViewRegistry& sceneViewRegistry = this->application.sceneViewRegistry;
-    const SceneViewRegistry& sceneViewRegistryConst =
-        this->application.sceneViewRegistry;
 
     imguiRenderer.setDefaultLayout(panelRegistry.getDefaultLayout());
 
+    // Views already warned about having no camera, so each warns once.
+    std::set<SceneViewHandle> viewsWithoutCamera;
+
     auto startTime = std::chrono::high_resolution_clock::now();
     auto currentTime = startTime;
     u32 frameIndex = 0;
@@ -148,8 +150,8 @@ class Application::Impl {
           graph.importImage(renderContext.getCurrentImage(), Access::Present);
 
       std::map<RenderTargetHandle, ImageRef> viewTargets;
-      for (SceneViewHandle handle : sceneViewRegistryConst.GetRenderQueue()) {
-        const SceneView& view = sceneViewRegistryConst.get(handle);
+      for (SceneViewHandle handle : sceneViewRegistry.GetRenderQueue()) {
+        const SceneView& view = sceneViewRegistry.peek(handle);
         if (!sceneRegistry.isAlive(view.scene) ||
             !renderTargetPool.isAlive(view.target)) {
           continue;
@@ -172,12 +174,23 @@ class Application::Impl {
                                   : vk::AttachmentLoadOp::eLoad,
                               {color.r, color.g, color.b, color.a});
             },
-            [&sceneRenderer, &sceneViewRegistryConst,
-             handle](vk::CommandBuffer commandBuffer) {
-              const SceneView& view = sceneViewRegistryConst.get(handle);
-              if (view.camera) {
-                sceneRenderer.render(commandBuffer, view);
+            [&sceneRenderer, &sceneRegistry, &sceneViewRegistry,
+             &viewsWithoutCamera, handle](vk::CommandBuffer commandBuffer) {
+              const SceneView& view = sceneViewRegistry.peek(handle);
+              Entity camera =
+                  view.camera ? view.camera
+                              : sceneRegistry.get(view.scene).getActiveCamera();
+              // No camera to look through: the target is just cleared.
+              if (!camera) {
+                if (viewsWithoutCamera.insert(handle).second) {
+                  log::warning(
+                      "scene view has no camera and its scene has no active "
+                      "camera; it will only be cleared (see "
+                      "Scene::createCamera)");
                 }
+                return;
+              }
+              sceneRenderer.render(commandBuffer, view, camera);
             });
       }
 

engine/src/rendering/imgui_renderer.cpp

@@ -91,12 +91,13 @@ void ImGuiRenderer::beginFrame() {
 }
 
 ImTextureID ImGuiRenderer::getTextureId(RenderTargetHandle handle) {
-  vk::ImageView view =
-      resources.renderTargetPool.get(handle).getImage().getView();
+  const RenderTarget& target = resources.renderTargetPool.get(handle);
+  vk::ImageView view = target.getImage().getView();
 
   auto it = textures.find(handle.index);
   if (it != textures.end()) {
-    if (it->second.generation == handle.generation && it->second.view == view) {
+    if (it->second.generation == handle.generation &&
+        it->second.version == target.getVersion()) {
       return (ImTextureID)it->second.descriptorSet;
     }
     ImGui_ImplVulkan_RemoveTexture(it->second.descriptorSet);
@@ -107,7 +108,8 @@ ImTextureID ImGuiRenderer::getTextureId(RenderTargetHandle handle) {
   // left in once the scene pass has finished.
   VkDescriptorSet descriptorSet = ImGui_ImplVulkan_AddTexture(
       static_cast<VkImageView>(view), VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL);
-  textures[handle.index] = {handle.generation, view, descriptorSet};
+  textures[handle.index] = {handle.generation, target.getVersion(),
+                            descriptorSet};
   return (ImTextureID)descriptorSet;
 }
 
@@ -120,7 +122,7 @@ void ImGuiRenderer::releaseStaleTextures() {
 
     bool stale =
         !renderTargetPool.isAlive(handle) ||
-        renderTargetPool.get(handle).getImage().getView() != it->second.view;
+        renderTargetPool.get(handle).getVersion() != it->second.version;
     if (stale) {
       ImGui_ImplVulkan_RemoveTexture(it->second.descriptorSet);
       it = textures.erase(it);

engine/src/rendering/imgui_renderer.hpp

@@ -37,7 +37,7 @@ class ImGuiRenderer {
 
   struct Texture {
     u32 generation;
-    vk::ImageView view;
+    u32 version;
     VkDescriptorSet descriptorSet;
   };
 

engine/src/rendering/scene_renderer.cpp

@@ -14,19 +14,13 @@ SceneRenderer::SceneRenderer(const SceneRegistry& sceneRegistry,
       resources{resources},
       spriteRenderSystem{device, colorFormat, resources} {}
 
-SceneRenderer::~SceneRenderer() {}
-
 void SceneRenderer::beginFrame(u32 frameIndex) {
   this->spriteRenderSystem.beginFrame(frameIndex);
 }
 
 void SceneRenderer::render(vk::CommandBuffer commandBuffer,
-                           const SceneView& sceneView) {
-  const Scene& scene = this->sceneRegistry.get(sceneView.scene);
-  const entt::registry& registry = scene.registry;
-
-  entt::entity camera = sceneView.camera;
-  SOPHIA_ASSERT(registry.all_of<CameraComponent>(camera),
+                           const SceneView& sceneView, Entity camera) {
+  SOPHIA_ASSERT(camera.hasComponent<CameraComponent>(),
                 "camera does not have camera component!");
 
   vk::Extent2D extent =
@@ -34,17 +28,12 @@ void SceneRenderer::render(vk::CommandBuffer commandBuffer,
   float aspect =
       static_cast<float>(extent.width) / static_cast<float>(extent.height);
 
-  // The view matrix ignores the camera's scale; zoom is the projection's job.
-  glm::mat4 cameraWorld{1.f};
-  if (const auto* transform = registry.try_get<TransformComponent>(camera)) {
-    cameraWorld = glm::translate(glm::mat4{1.f}, transform->position) *
-                  glm::mat4_cast(transform->rotation);
-  }
   glm::mat4 viewProjection =
-      registry.get<CameraComponent>(camera).getProjection(aspect) *
-      glm::inverse(cameraWorld);
+      camera.getComponent<CameraComponent>().getViewProjection(
+          camera.getComponent<TransformComponent>(), aspect);
 
-  renderSprites(commandBuffer, scene, viewProjection);
+  renderSprites(commandBuffer, this->sceneRegistry.get(sceneView.scene),
+                viewProjection);
 
   // TODO: meshes. Group MeshComponent entities by mesh and draw each group
   // (instanced), as sprites are grouped by texture.
@@ -53,8 +42,7 @@ void SceneRenderer::render(vk::CommandBuffer commandBuffer,
 void SceneRenderer::renderSprites(vk::CommandBuffer commandBuffer,
                                   const Scene& scene,
                                   const glm::mat4& viewProjection) {
-  std::vector<SpriteDrawItem>& items = this->spriteDrawItems;
-  items.clear();
+  this->spriteDrawItems.clear();
 
   auto view =
       scene.registry.view<const TransformComponent, const SpriteComponent>();
@@ -63,28 +51,22 @@ void SceneRenderer::renderSprites(vk::CommandBuffer commandBuffer,
                                 ? sprite.texture
                                 : this->resources.whiteTexture;
 
-    // Unit quad -> sprite rectangle around its pivot -> world.
-    glm::mat4 model =
-        transform.mat4() *
-        glm::translate(glm::mat4{1.f},
-                       glm::vec3{-sprite.pivot * sprite.size, 0.f}) *
-        glm::scale(glm::mat4{1.f}, glm::vec3{sprite.size, 1.f});
-
-    items.push_back({sprite.sortOrder,
+    this->spriteDrawItems.push_back(
+        {sprite.sortOrder,
          transform.position.z,
          texture,
-                     {model, sprite.color, sprite.uvRect}});
+         {sprite.getModel(transform), sprite.color, sprite.uvRect}});
   }
 
   // Texture is the last key so that sprites whose order doesn't matter
   // relative to each other still end up in as few batches as possible.
-  std::ranges::sort(items, {}, [](const SpriteDrawItem& item) {
+  std::ranges::sort(this->spriteDrawItems, {}, [](const SpriteDrawItem& item) {
     return std::tuple{item.sortOrder, item.depth, item.texture};
   });
 
   this->spriteInstances.clear();
   this->spriteBatches.clear();
-  for (const SpriteDrawItem& item : items) {
+  for (const SpriteDrawItem& item : this->spriteDrawItems) {
     auto index = static_cast<u32>(this->spriteInstances.size());
     this->spriteInstances.push_back(item.instance);
 

engine/src/rendering/scene_renderer.hpp

@@ -21,14 +21,15 @@ class SceneRenderer {
 
   SceneRenderer(const SceneRegistry& sceneRegistry, ResourceRegistry& resources,
                 Device& device, vk::Format colorFormat);
-  ~SceneRenderer();
 
   // Call once per frame, before any render().
   void beginFrame(u32 frameIndex);
 
-  // Records `sceneView` into `commandBuffer`. Rendering into the view's
-  // target must already have begun.
-  void render(vk::CommandBuffer commandBuffer, const SceneView& sceneView);
+  // Records `sceneView` as seen through `camera` (an entity of the view's
+  // scene with a CameraComponent) into `commandBuffer`. Rendering into the
+  // view's target must already have begun.
+  void render(vk::CommandBuffer commandBuffer, const SceneView& sceneView,
+              Entity camera);
 
  private:
   struct SpriteDrawItem {

engine/src/resources/render_target.cpp

@@ -39,6 +39,7 @@ void RenderTarget::applyPendingResize() {
 }
 
 void RenderTarget::create(u32 width, u32 height) {
+  this->version++;
   this->image = Image::Builder(this->device)
                     .setExtent(width, height)
                     .setFormat(this->format)

engine/src/resources/render_target.hpp

@@ -27,6 +27,7 @@ class RenderTarget {
   Image& getImage() const { return *this->image; }
 
   vk::Extent2D getExtent() const;
+  u32 getVersion() const { return this->version; }
 
   void requestResize(u32 width, u32 height);
 
@@ -46,6 +47,7 @@ class RenderTarget {
   std::unique_ptr<Image> image;
 
   std::optional<vk::Extent2D> pendingExtent;
+  u32 version = 0;
 };
 
 }  // namespace sophia

engine/src/scene/scene.cpp

@@ -16,6 +16,24 @@ Entity Scene::createEntity(const std::string& name) {
   return entity;
 }
 
+Entity Scene::createCamera(const std::string& name) {
+  Entity camera = createEntity(name);
+  camera.addComponent<CameraComponent>();
+  if (this->activeCamera == entt::null) {
+    this->activeCamera = camera;
+  }
+  return camera;
+}
+
+Entity Scene::getActiveCamera() {
+  if (this->activeCamera == entt::null) {
+    return {};
+  }
+  return {this->activeCamera, this};
+}
+
+void Scene::setActiveCamera(Entity camera) { this->activeCamera = camera; }
+
 void Scene::destroyEntity(Entity entity) {
   if (this->activeCamera == entity) {
     this->activeCamera = entt::null;

examples/boids_2d/main.cpp

@@ -87,6 +87,8 @@ class Boids2D : public sophia::Application {
         [this](sophia::KeyReleasedEvent& e) {
           setScrollKeyHeld(e.getKeyCode(), false);
         });
+
+    debugUI().show();
   }
 
   void onCreate() override {
@@ -110,8 +112,7 @@ class Boids2D : public sophia::Application {
     sceneHandle = scenes().create();
     sophia::Scene& scene = scenes().get(sceneHandle);
 
-    cameraEntity = scene.createEntity("Camera");
-    cameraEntity.addComponent<sophia::CameraComponent>();
+    cameraEntity = scene.createCamera();
 
     std::uniform_real_distribution<float> tint{0.0f, 1.0f};
     for (Boid& boid : boids) {
@@ -127,7 +128,6 @@ class Boids2D : public sophia::Application {
     target = resources().create<sophia::RenderTarget>();
     views().create({.scene = sceneHandle,
                     .target = target,
-                    .camera = cameraEntity,
                     .clearColor = {0.01f, 0.01f, 0.02f, 1.0f}});
 
     panels().emplace<ViewportPanel>(ui(), target);

examples/image_viewer/main.cpp

@@ -40,8 +40,7 @@ class ImageViewer : public sophia::Application {
     sophia::SceneHandle sceneHandle = scenes().create();
     sophia::Scene& scene = scenes().get(sceneHandle);
 
-    camera = scene.createEntity("Camera");
-    camera.addComponent<sophia::CameraComponent>();
+    camera = scene.createCamera();
 
     sophia::TextureHandle texture = resources().load<sophia::Texture>(path);
     imageSize = resources().getExtent(texture);
@@ -54,7 +53,6 @@ class ImageViewer : public sophia::Application {
     target = resources().create<sophia::RenderTarget>();
     views().create({.scene = sceneHandle,
                     .target = target,
-                    .camera = camera,
                     .clearColor = {0.1f, 0.1f, 0.15f, 1.f}});
 
     panels().emplace<ViewportPanel>(ui(), target);