implement document resize with menu and dialog

src/canvas.h

@@ -29,12 +29,27 @@ public:
         std::unique_ptr<uint8_t[]> image[6] = SIXPLETTE(0);
         glm::vec4 m_dirty_box[6] = SIXPLETTE(glm::vec4(0));
         bool m_dirty_face[6] = SIXPLETTE(false);
+        int width = 0;
+        int height = 0;
         void create(int w, int h)
         {
             for (int i = 0; i < 6; i++)
+            {
                 image[i] = std::make_unique<uint8_t[]>(w*h*4);
+                std::fill_n(image[i].get(), w*h*4, 0);
+            }
+        }
+        void clear()
+        {
+            for (int i = 0; i < 6; i++)
+            {
+                m_dirty_face[i] = false;
+                m_dirty_box[i] = glm::vec4(0);
+                std::fill_n(image[i].get(), width*height*4, 0);
+            }
         }
     };
+    void resize(int width, int height);
     bool create(int width, int height, std::string name);
     void clear(const glm::vec4& c);
     Snapshot snapshot(std::string data_path);
@@ -182,6 +197,7 @@ public:
     void stroke_cancel();
     void stroke_commit();
     void clear(const glm::vec4& color = { 1, 1, 1, 0 });
+    void clear_all();
     void pick_start();
     void pick_update(int plane);
     glm::vec4 pick_get(glm::vec2 canvas_loc);