diff -up fltk-1.3.x-r8732/src/Fl_win32.cxx.hwheel fltk-1.3.x-r8732/src/Fl_win32.cxx

--- fltk-1.3.x-r8732/src/Fl_win32.cxx.hwheel	2011-05-21 23:55:59.000000000 +0200

+++ fltk-1.3.x-r8732/src/Fl_win32.cxx	2011-05-24 13:37:31.109341034 +0200

@@ -1125,12 +1286,28 @@ static LRESULT CALLBACK WndProc(HWND hWn

   case WM_MOUSEWHEEL: {

     static int delta = 0; // running total of all motion

     delta += (SHORT)(HIWORD(wParam));

+    Fl::e_dx = 0;

     Fl::e_dy = -delta / WHEEL_DELTA;

     delta += Fl::e_dy * WHEEL_DELTA;

     if (Fl::e_dy) Fl::handle(FL_MOUSEWHEEL, window);

     return 0;

   }

+// This is only defined on Vista and upwards...

+#ifndef WM_MOUSEHWHEEL

+#define WM_MOUSEHWHEEL 0x020E

+#endif

+

+  case WM_MOUSEHWHEEL: {

+    static int delta = 0; // running total of all motion

+    delta += (SHORT)(HIWORD(wParam));

+    Fl::e_dy = 0;

+    Fl::e_dx = delta / WHEEL_DELTA;

+    delta -= Fl::e_dx * WHEEL_DELTA;

+    if (Fl::e_dx) Fl::handle(FL_MOUSEWHEEL, window);

+    return 0;

+  }

+

   case WM_GETMINMAXINFO:

     Fl_X::i(window)->set_minmax((LPMINMAXINFO)lParam);

     break;

diff -up fltk-1.3.x-r8732/src/Fl_x.cxx.hwheel fltk-1.3.x-r8732/src/Fl_x.cxx

--- fltk-1.3.x-r8732/src/Fl_x.cxx.hwheel	2011-05-23 21:40:23.000000000 +0200

+++ fltk-1.3.x-r8732/src/Fl_x.cxx	2011-05-24 13:36:49.635113914 +0200

@@ -1441,12 +1608,19 @@ int fl_handle(const XEvent& thisevent)

   case ButtonPress:

     Fl::e_keysym = FL_Button + xevent.xbutton.button;

     set_event_xy();

+    Fl::e_dx = Fl::e_dy = 0;

     if (xevent.xbutton.button == Button4) {

       Fl::e_dy = -1; // Up

       event = FL_MOUSEWHEEL;

     } else if (xevent.xbutton.button == Button5) {

       Fl::e_dy = +1; // Down

       event = FL_MOUSEWHEEL;

+    } else if (xevent.xbutton.button == 6) {

+      Fl::e_dx = -1; // Left

+      event = FL_MOUSEWHEEL;

+    } else if (xevent.xbutton.button == 7) {

+      Fl::e_dx = +1; // Right

+      event = FL_MOUSEWHEEL;

     } else {

       Fl::e_state |= (FL_BUTTON1 << (xevent.xbutton.button-1));

       event = FL_PUSH;