GDK W32: Support smooth scrolling

Set delta_x or delta_y for GdkScrollEvent.
HIWORD (wParam) in WM_MOUSE(H)WHEEL is the scroll delta.
A delta value of WHEEL_DELTA (which is 120) means scrolling
one full unit of something (for example, a line).

The delta should also be multiplied by the value that the
SystemParametersInfo (SPI_GETWHEELSCROLL(LINES|CHARS), 0, &value, 0)
call gives back, unless it gives back 0xffffffff, in which case
it indicates that scrolling is page- or screen-based, not line-based
(GDK doesn't support that at the moment).

Also, all deltas should be inverted, since MS sends negative deltas
when scrolling down (rotating the wheel back, in the direction of
the user).

With deltas set the mode should be set to GDK_SCROLL_SMOOTH.

Fixes issue 1263.

diff --git a/gdk/win32/gdkevents-win32.c b/gdk/win32/gdkevents-win32.c
index c050b9d64c4173a3197d9333fae7842e701885c2..beaac53f49afcb03b2ed3c99f823088771d8ccfc 100644 (file)
--- a/gdk/win32/gdkevents-win32.c
+++ b/gdk/win32/gdkevents-win32.c
@@ -3071,13 +3071,35 @@ gdk_event_translate (MSG  *msg,
 
       event = gdk_event_new (GDK_SCROLL);
       event->scroll.window = window;
+      event->scroll.direction = GDK_SCROLL_SMOOTH;
 
       if (msg->message == WM_MOUSEWHEEL)
-         event->scroll.direction = (((short) HIWORD (msg->wParam)) > 0) ?
-           GDK_SCROLL_UP : GDK_SCROLL_DOWN;
+        {
+          UINT lines_multiplier = 3;
+          event->scroll.delta_y = (gdouble) GET_WHEEL_DELTA_WPARAM (msg->wParam) / (gdouble) WHEEL_DELTA;
+          /* -1 means that we should scroll in screens, not lines.
+           * Right now GDK doesn't support that.
+           */
+          if (SystemParametersInfo (SPI_GETWHEELSCROLLLINES, 0, &lines_multiplier, 0) &&
+              lines_multiplier != (UINT) -1)
+            event->scroll.delta_y *= (gdouble) lines_multiplier;
+        }
       else if (msg->message == WM_MOUSEHWHEEL)
-         event->scroll.direction = (((short) HIWORD (msg->wParam)) > 0) ?
-           GDK_SCROLL_RIGHT : GDK_SCROLL_LEFT;
+        {
+          UINT chars_multiplier = 3;
+          event->scroll.delta_x = (gdouble) GET_WHEEL_DELTA_WPARAM (msg->wParam) / (gdouble) WHEEL_DELTA;
+          /* There doesn't seem to be any indication that
+           * h-scroll has an equivalent of the "screen" mode,
+           * indicated by multiplier being (UINT) -1.
+           */
+          if (SystemParametersInfo (SPI_GETWHEELSCROLLCHARS, 0, &chars_multiplier, 0))
+            event->scroll.delta_x *= (gdouble) chars_multiplier;
+        }
+      /* It seems that delta values given by Windows are
+       * inverted (positive delta scrolls up, not down).
+       */
+      event->scroll.delta_x *= -1.0;
+      event->scroll.delta_y *= -1.0;
       event->scroll.time = _gdk_win32_get_next_tick (msg->time);
       event->scroll.x = (gint16) point.x / impl->window_scale;
       event->scroll.y = (gint16) point.y / impl->window_scale;