+static int
+can_scroll (struct scrollbar_instance* scrollbar)
+{
+ return scrollbar != NULL
+ && IsWindowVisible (SCROLLBAR_MSW_HANDLE (scrollbar))
+ && IsWindowEnabled (SCROLLBAR_MSW_HANDLE (scrollbar));
+}
+
+int
+mswindows_handle_mousewheel_event (Lisp_Object frame, int keys, int delta,
+ POINTS where)
+{
+ int hasVertBar, hasHorzBar; /* Indicates presence of scroll bars */
+ unsigned wheelScrollLines = 0; /* Number of lines per wheel notch */
+ Lisp_Object win, corpore, sano;
+ struct window_mirror *mirror;
+ int mene, _mene, tekel, upharsin;
+ Bufpos mens, sana;
+ Charcount in;
+ struct window *needle_in_haystack = 0;
+ POINT donde_esta;
+
+ donde_esta.x = where.x;
+ donde_esta.y = where.y;
+
+ /* Find the window to scroll */
+
+ /* The mouse event could actually occur outside of the emacs
+ frame. */
+ if (ScreenToClient (FRAME_MSWINDOWS_HANDLE (XFRAME (frame)),
+ &donde_esta) != 0)
+ {
+ /* stderr_out ("donde_esta: %d %d\n", donde_esta.x, donde_esta.y); */
+ pixel_to_glyph_translation (XFRAME (frame), donde_esta.x, donde_esta.y,
+ &mene, &_mene, &tekel, &upharsin,
+ &needle_in_haystack,
+ &mens, &sana, &in, &corpore, &sano);
+
+ if (needle_in_haystack)
+ {
+ XSETWINDOW (win, needle_in_haystack);
+ /* stderr_out ("found needle\n");
+ debug_print (win); */
+ }
+ }
+
+ if (!needle_in_haystack)
+ {
+ win = FRAME_SELECTED_WINDOW (XFRAME (frame));
+ needle_in_haystack = XWINDOW (win);
+ }
+
+ mirror = find_window_mirror (needle_in_haystack);
+
+ /* Check that there is something to scroll */
+ hasVertBar = can_scroll (mirror->scrollbar_vertical_instance);
+ hasHorzBar = can_scroll (mirror->scrollbar_horizontal_instance);
+ if (!hasVertBar && !hasHorzBar)
+ return FALSE;
+
+ /* No support for panning and zooming, so ignore */
+ if (keys & (MK_SHIFT | MK_CONTROL))
+ return FALSE;
+
+ /* Get the number of lines per wheel delta */
+ SystemParametersInfo (SPI_GETWHEELSCROLLLINES, 0, &wheelScrollLines, 0);
+
+ /* Calculate the amount to scroll */
+ if (wheelScrollLines == WHEEL_PAGESCROLL)
+ {
+ /* Scroll by a page */
+ Lisp_Object function;
+ if (hasVertBar)
+ function = delta > 0 ? Qscrollbar_page_up : Qscrollbar_page_down;
+ else
+ function = delta > 0 ? Qscrollbar_page_left : Qscrollbar_page_right;
+ mswindows_enqueue_misc_user_event (frame, function, Fcons (win, Qnil));
+ }
+ else /* Scroll by a number of lines */
+ {
+ /* Calc the number of lines to scroll */
+ int toScroll = MulDiv (delta, wheelScrollLines, WHEEL_DELTA);
+
+ /* Do the scroll */
+ Lisp_Object function;
+ if (hasVertBar)
+ function = delta > 0 ? Qscrollbar_line_up : Qscrollbar_line_down;
+ else
+ function = delta > 0 ? Qscrollbar_char_left : Qscrollbar_char_right;
+ if (toScroll < 0)
+ toScroll = -toScroll;
+ while (toScroll--)
+ mswindows_enqueue_misc_user_event (frame, function, win);
+ }
+
+ return TRUE;
+}
+