save and restore layers image when context is lost in Android

engine/canvas.h

@@ -20,44 +20,11 @@ public:
     {
         std::unique_ptr<uint8_t[]> image[6];
     };
-    bool create(int width, int height, std::string name)
-    {
-        for (int i = 0; i < 6; i++)
-        {
-            m_rtt[i].create(width, height);
-            m_rtt[i].bindFramebuffer();
-            m_rtt[i].clear();
-            m_rtt[i].unbindFramebuffer();
-        }
-        return true;
-    }
-    void clear(const glm::vec4& c)
-    {
-        // push clear color state
-        GLfloat cc[4];
-        glGetFloatv(GL_COLOR_CLEAR_VALUE, cc);
-        glClearColor(c.r, c.g, c.b, c.a);
-        
-        for (int i = 0; i < 6; i++)
-        {
-            m_rtt[i].bindFramebuffer();
-            glClear(GL_COLOR_BUFFER_BIT);
-            m_rtt[i].unbindFramebuffer();
-        }
-        
-        // restore clear color state
-        glClearColor(cc[0], cc[1], cc[2], cc[3]);
-    }
-    Snapshot snapshot()
-    {
-        Snapshot snap;
-        for (int i = 0; i < 6; i++)
-        {
-            snap.image[i] = std::make_unique<uint8_t[]>(m_rtt[i].bytes());
-            m_rtt[i].readTextureData(snap.image[i].get());
-        }
-        return snap;
-    }
+    bool create(int width, int height, std::string name);
+    void clear(const glm::vec4& c);
+    Snapshot snapshot(std::string data_path);
+    void restore(const Snapshot& snap);
+    void destroy();
 };
 
 class Canvas
@@ -105,8 +72,9 @@ public:
     void stroke_end();
     void stroke_commit();
     void clear(const glm::vec4& color = { 1, 1, 1, 1 });
-    void snapshot_save();
+    void snapshot_save(std::string data_path);
     void snapshot_restore();
+    void clear_context();
 };