+static gboolean
+ev_view_drag_update_momentum (EvView *view)
+{
+ int i;
+ if (!view->drag_info.in_drag)
+ return FALSE;
+
+ for (i = DRAG_HISTORY - 1; i > 0; i--) {
+ view->drag_info.buffer[i].x = view->drag_info.buffer[i-1].x;
+ view->drag_info.buffer[i].y = view->drag_info.buffer[i-1].y;
+ }
+
+ /* Momentum is a moving average of 10ms granularity over
+ * the last 100ms with each 10ms stored in buffer.
+ */
+
+ view->drag_info.momentum.x = (view->drag_info.buffer[DRAG_HISTORY - 1].x - view->drag_info.buffer[0].x);
+ view->drag_info.momentum.y = (view->drag_info.buffer[DRAG_HISTORY - 1].y - view->drag_info.buffer[0].y);
+
+ return TRUE;
+}
+
+static gboolean
+ev_view_scroll_drag_release (EvView *view)
+{
+ gdouble dhadj_value, dvadj_value;
+ gdouble oldhadjustment, oldvadjustment;
+
+ view->drag_info.momentum.x /= 1.2;
+ view->drag_info.momentum.y /= 1.2; /* Alter these constants to change "friction" */
+
+ dhadj_value = view->hadjustment->page_size *
+ (gdouble)view->drag_info.momentum.x / GTK_WIDGET (view)->allocation.width;
+ dvadj_value = view->vadjustment->page_size *
+ (gdouble)view->drag_info.momentum.y / GTK_WIDGET (view)->allocation.height;
+
+ oldhadjustment = gtk_adjustment_get_value (view->hadjustment);
+ oldvadjustment = gtk_adjustment_get_value (view->vadjustment);
+
+ if (((oldhadjustment + dhadj_value) > (view->hadjustment->upper - view->hadjustment->page_size)) ||
+ ((oldhadjustment + dhadj_value) < 0))
+ view->drag_info.momentum.x *= -0.5; /* 0.5 rather than 1 means the edges absorb some momentum */
+ if (((oldvadjustment + dvadj_value) > (view->vadjustment->upper - view->vadjustment->page_size)) ||
+ ((oldvadjustment + dvadj_value) < 0))
+ view->drag_info.momentum.y *= -0.5;
+
+ gtk_adjustment_set_value (view->hadjustment,
+ MIN (oldhadjustment + dhadj_value,
+ view->hadjustment->upper - view->hadjustment->page_size));
+ gtk_adjustment_set_value (view->vadjustment,
+ MIN (oldvadjustment + dvadj_value,
+ view->vadjustment->upper - view->vadjustment->page_size));
+
+ if (((view->drag_info.momentum.x < 1) && (view->drag_info.momentum.x > -1)) &&
+ ((view->drag_info.momentum.y < 1) && (view->drag_info.momentum.y > -1)))
+ return FALSE;
+ else
+ return TRUE;
+}
+