zoom using mousewheel

Fltk/Opengl_Window.cpp

-// $Id: Opengl_Window.cpp,v 1.70 2006-08-27 23:10:36 geuzaine Exp $
+// $Id: Opengl_Window.cpp,v 1.71 2006-10-10 01:33:26 geuzaine Exp $
 //
 // Copyright (C) 1997-2006 C. Geuzaine, J.-F. Remacle
 //
@@ -178,8 +178,6 @@ void Opengl_Window::draw()
 
 int Opengl_Window::handle(int event)
 {
-  double dx, dy;
-
   switch (event) {
 
   case FL_FOCUS: // accept the focus when I'm asked if I want it
@@ -282,10 +280,31 @@ int Opengl_Window::handle(int event)
     prev.set();
     return 1;
 
+  case FL_MOUSEWHEEL:
+    curr.set();
+    {
+      double dy = Fl::event_dy();
+      double fact = (5. * CTX.zoom_factor * fabs(dy) + h()) / (double)h();
+      CTX.s[0] *= ((dy > 0) ? fact : 1./fact);
+      CTX.s[1] = CTX.s[0];
+      CTX.s[2] = CTX.s[0];
+      click.recenter();
+      CTX.draw_rotation_center = 1;
+      if(CTX.fast_redraw) {
+	CTX.mesh.draw = 0;
+	CTX.post.draw = 0;
+      }
+      redraw();
+    }
+    prev.set();
+    WID->update_manip_window();
+    return 1;
+
   case FL_DRAG:
     curr.set();
-    dx = curr.win[0] - prev.win[0];
-    dy = curr.win[1] - prev.win[1];
+    {
+      double dx = curr.win[0] - prev.win[0];
+      double dy = curr.win[1] - prev.win[1];
       if(LassoMode) {
 	redraw();
       }
@@ -326,6 +345,7 @@ int Opengl_Window::handle(int event)
 	}
 	redraw();
       }
+    }
     prev.set();
     WID->update_manip_window();
     return 1;