implement pen and erase as strategy pattern introducing the CanvasMode classes

engine/canvas.h

@@ -5,6 +5,7 @@
 #include "shape.h"
 #include "brush.h"
 #include "action.h"
+#include "canvas_modes.h"
 
 NS_START
 
@@ -66,8 +67,17 @@ public:
     Sampler m_sampler_mask;
     glm::vec2 m_cam_rot;
     float m_cam_fov = 85;
-    enum class kPenState { Draw, Erase, Line, Camera };
-    kPenState m_state{ kPenState::Draw };
+
+    enum class kCanvasMode { Draw, Erase, Line, Camera };
+    kCanvasMode m_state{ kCanvasMode::Draw };
+    static CanvasMode* modes[];
+    CanvasMode* m_mode;
+    static void set_mode(kCanvasMode mode)
+    {
+        I->m_mode = modes[(int)mode];
+        I->m_state = mode;
+        I->m_mode->canvas = I;
+    }
 
     GLuint cube_id;
     RTT m_latlong;
@@ -96,7 +106,6 @@ public:
     void preview_generate();
 };
 
-
 class ActionStroke : public Action
 {
 public: