add ui and viewport scale option, fix combobox items height from parent

src/node_canvas.h

@@ -19,6 +19,7 @@ public:
     Plane m_grid;
     glm::vec2 m_outline_pan;
     int m_grid_divs = 30;
+    float m_density = 1.f;
     virtual Node* clone_instantiate() const override;
     virtual void init() override;
     virtual void restore_context() override;
@@ -29,4 +30,6 @@ public:
     virtual void destroy_immediate() override;
     virtual void on_tick(float dt) override;
     void reset_camera();
+    void create_buffers();
+    void set_density(float d);
 };