remove direct use of rtt and dirty area from the layer

src/rtt.h

@@ -24,7 +24,7 @@ public:
     void copy(const RTT& source);
     // copy a region
     void copy(const RTT& source, const glm::vec4& rect);
-    void resize(int width, int height);
+    bool resize(int width, int height);
     bool create(int width, int height, int tex = -1, GLint internal_format = GL_RGBA8, bool depth_buffer = false);
     bool recreate() { return create(w, h); }
     void clear(glm::vec4 color = glm::vec4(0));