Expand all graphics retrieval with bitmap and vram

src/gui/canvas.h

@@ -4,6 +4,7 @@
 #include <imgui/imgui.h>
 
 #include <cmath>
+#include <memory>
 #include <string>
 
 namespace yaze {
@@ -11,18 +12,30 @@ namespace gui {
 class Canvas {
  public:
   Canvas() = default;
+  Canvas(ImVec2 canvas_size)
+      : canvas_sz_(canvas_size), custom_canvas_size_(true) {}
 
   void Update();
 
+  void DrawBackground();
+  void UpdateContext();
+  void DrawGrid();
+  void DrawOverlay();  // last
+
  private:
   bool enable_grid_ = true;
   bool enable_context_menu_ = true;
   bool dragging_select_ = false;
+  bool custom_canvas_size_ = false;
 
   std::string title_;
 
+  ImDrawList* draw_list_;
   ImVector<ImVec2> points_;
   ImVec2 scrolling_;
+  ImVec2 canvas_sz_;
+  ImVec2 canvas_p0_;
+  ImVec2 canvas_p1_;
 };
 }  // namespace gui
 }  // namespace yaze