feat: add canvas rework

destrum/include/destrum/AppLayer.h

@@ -1,6 +1,10 @@
 #ifndef DESTRUM_APPLAYER_H
 #define DESTRUM_APPLAYER_H
 
+#include <optional>
+
+#include <destrum/Components/UI/CanvasFrame.h>
+
 class Camera;
 class GameRenderer;
 
@@ -25,6 +29,7 @@ public:
     [[nodiscard]] virtual Camera* viewCamera() { return nullptr; }
     [[nodiscard]] virtual bool hostsViewport() const { return false; }
     [[nodiscard]] virtual InputFocus gameInputFocus() const { return {}; }
+    [[nodiscard]] virtual std::optional<CanvasFrame> canvasFrame() const { return std::nullopt; }
 };
 
 #endif // DESTRUM_APPLAYER_H

destrum/include/destrum/Components/UI/Canvas.h

@@ -1,6 +1,7 @@
 #ifndef DESTRUM_CANVAS_H
 #define DESTRUM_CANVAS_H
 
+#include <destrum/Components/UI/CanvasFrame.h>
 #include <destrum/Components/UI/RectTransform.h>
 #include <destrum/ObjectModel/Component.h>
 
@@ -22,6 +23,7 @@ public:
     void Start() override;
     void Render(const RenderContext& ctx) override;
     void Draw(const glm::vec2& screenSize);
+    void Draw(const CanvasFrame& frame);
 
     void Reflect(FieldVisitor& v) override;
 

destrum/include/destrum/Components/UI/CanvasFrame.h

@@ -0,0 +1,13 @@
+#ifndef DESTRUM_CANVASFRAME_H
+#define DESTRUM_CANVASFRAME_H
+
+#include <glm/glm.hpp>
+
+// Where canvases lay out, in draw image pixels: a resolution sized screen at min, drawn zoom times larger
+struct CanvasFrame {
+    glm::vec2 min{0.0f};
+    glm::vec2 resolution{0.0f};
+    float zoom{1.0f};
+};
+
+#endif // DESTRUM_CANVASFRAME_H

destrum/include/destrum/Components/UI/RectTransform.h

@@ -43,6 +43,8 @@ public:
     // Where the canvas last drew this object
     [[nodiscard]] const UIRect& GetScreenRect() const { return m_ScreenRect; }
     [[nodiscard]] const UIRect& GetParentRect() const { return m_ParentRect; }
+    // Screen pixels per canvas unit at the last draw
+    [[nodiscard]] float GetScreenScale() const { return m_LastScale; }
     void SetScreenRect(const UIRect& rect, const UIRect& parentRect, float scale)
     {
         m_ScreenRect = rect;

destrum/include/destrum/Graphics/RenderContext.h

@@ -1,12 +1,17 @@
 #ifndef RENDERCONTEXT_H
 #define RENDERCONTEXT_H
 
+#include <optional>
+
+#include <destrum/Components/UI/CanvasFrame.h>
 #include <destrum/Graphics/Renderer.h>
 
 struct RenderContext {
     GameRenderer& renderer;
     const Camera& camera;
     const GameRenderer::SceneData& sceneData;
+    // Unset: canvases fill the draw image
+    std::optional<CanvasFrame> canvasFrame{};
 };
 
 #endif //RENDERCONTEXT_H

destrum/src/App.cpp

@@ -378,6 +378,7 @@ void App::renderFrame()
         .renderer = renderer,
         .camera = camera,
         .sceneData = sceneData,
+        .canvasFrame = layer ? layer->canvasFrame() : std::nullopt,
     });
     renderer.endDrawing();
     renderer.draw(cmd, gfxDevice, camera, sceneData);

destrum/src/Components/UI/Canvas.cpp

@@ -54,19 +54,29 @@ Canvas* Canvas::FindFor(GameObject& object)
 
 void Canvas::Render(const RenderContext& ctx)
 {
+    if (ctx.canvasFrame) {
+        Draw(*ctx.canvasFrame);
+        return;
+    }
     const VkExtent3D extent = ctx.renderer.getDrawImage().extent;
     Draw(glm::vec2{static_cast<float>(extent.width), static_cast<float>(extent.height)});
 }
 
 void Canvas::Draw(const glm::vec2& screenSize)
+{
+    Draw(CanvasFrame{.resolution = screenSize});
+}
+
+void Canvas::Draw(const CanvasFrame& frame)
 {
     ZoneScopedN("Canvas::Draw");
 
-    const UIRect screenRect{.min = glm::vec2{0.0f}, .size = screenSize};
+    const UIRect screenRect{.min = frame.min, .size = frame.resolution * frame.zoom};
+    const float scale = GetScale(frame.resolution) * frame.zoom;
     if (auto* rectTransform = GetGameObject()->GetComponent<RectTransform>()) {
-        rectTransform->SetScreenRect(screenRect, screenRect, GetScale(screenSize));
+        rectTransform->SetScreenRect(screenRect, screenRect, scale);
     }
-    DrawObject(*GetGameObject(), screenRect, GetScale(screenSize), true);
+    DrawObject(*GetGameObject(), screenRect, scale, true);
 }
 
 float Canvas::GetScale(const glm::vec2& screenSize) const