Avoid server roundtrip on wheel events from scroll bars on XI2

* src/xterm.c (handle_one_xevent): Translate coordinates for
scroll bars correctly when handling XI2 wheel events.

diff --git a/src/xterm.c b/src/xterm.c
index 6d658cf20423197ff5dd1e9d5e9412ef0bf103d3..ea86b7f8033e79a48779ea1db4e84945ff986987 100644 (file)
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -16863,6 +16863,9 @@ handle_one_xevent (struct x_display_info *dpyinfo,
                      double delta, scroll_unit;
                      int scroll_height;
                      Lisp_Object window;
+                     struct scroll_bar *bar;
+
+                     bar = NULL;
 
                      /* See the comment on top of
                         x_init_master_valuators for more details on how
@@ -16880,9 +16883,8 @@ handle_one_xevent (struct x_display_info *dpyinfo,
                              if (!f)
                                {
 #if defined USE_MOTIF || !defined USE_TOOLKIT_SCROLL_BARS
-                                 struct scroll_bar *bar
-                                   = x_window_to_scroll_bar (xi_event->display,
-                                                             xev->event, 2);
+                                 bar = x_window_to_scroll_bar (dpyinfo->display,
+                                                               xev->event, 2);
 
                                  if (bar)
                                    f = WINDOW_XFRAME (XWINDOW (bar->window));
@@ -16899,11 +16901,26 @@ handle_one_xevent (struct x_display_info *dpyinfo,
 #endif
 
                          if (FRAME_X_WINDOW (f) != xev->event)
-                           XTranslateCoordinates (dpyinfo->display,
-                                                  xev->event, FRAME_X_WINDOW (f),
-                                                  lrint (xev->event_x),
-                                                  lrint (xev->event_y),
-                                                  &real_x, &real_y, &dummy);
+                           {
+                             if (!bar)
+                               bar = x_window_to_scroll_bar (dpyinfo->display, xev->event, 2);
+
+                             /* If this is a scroll bar, compute the
+                                actual position directly to avoid an
+                                extra roundtrip.  */
+
+                             if (bar)
+                               {
+                                 real_x = lrint (xev->event_x + bar->left);
+                                 real_y = lrint (xev->event_y + bar->top);
+                               }
+                             else
+                               XTranslateCoordinates (dpyinfo->display,
+                                                      xev->event, FRAME_X_WINDOW (f),
+                                                      lrint (xev->event_x),
+                                                      lrint (xev->event_y),
+                                                      &real_x, &real_y, &dummy);
+                           }
                          else
                            {
                              real_x = lrint (xev->event_x);