implement zooming

graphics.h

@@ -39,9 +39,15 @@ namespace Mandelbrot {
         Vec2mp to;
         bool running;
 
+        bool mouseDown;
+        Vec2i m_start;
+        Vec2i m_end;
+
         Graphics(int w, int h, std::string title);
         void plot(Mandelbrotc const &m);
         void mainLoop();
         void drawPoint(const Vec2i &pos, const rgb &col);
+        void drawSelectionRectangle();
+        void zoom(Mandelbrotc &m);
     };
 } // namespace Mandelbrot