Reuse image data instead of fetching it every time off the GPU

src/graphics/ui/elements/Canvas.hpp

@@ -15,11 +15,15 @@ namespace gui {
 
         void draw(const DrawContext& pctx, const Assets& assets) override;
 
-        [[nodiscard]] std::shared_ptr<::Texture> texture() const {
+        [[nodiscard]] auto texture() const {
             return mTexture;
         }
+
+        [[nodiscard]] auto data() const {
+            return mData;
+        }
     private:
         std::shared_ptr<::Texture> mTexture;
-        std::unique_ptr<ImageData> mData;
+        std::shared_ptr<ImageData> mData;
     };
 }