From 907f3a4f8d83c228a3be3772a3cb7d5079261752 Mon Sep 17 00:00:00 2001
From: Po Lu <luangruo@yahoo.com>
Date: Tue, 14 Jun 2022 09:41:59 +0800
Subject: [PATCH] Use coordinates provided by DND messages if available

This avoids an extra sync, which matters when dropping onto
Emacs running over a slow connection.

* src/xselect.c (x_handle_dnd_message): New args
`root_window_coords', `root_x' and `root_y'.
* src/xterm.c (x_coords_from_dnd_message): New function.
(handle_one_xevent): Pass root window coordinates to
x_handle_dnd_message.
* src/xterm.h: Update prototypes.
---
 src/xselect.c | 14 ++++++++++++--
 src/xterm.c   | 40 +++++++++++++++++++++++++++++++++++++++-
 src/xterm.h   |  3 ++-
 3 files changed, 53 insertions(+), 4 deletions(-)

diff --git a/src/xselect.c b/src/xselect.c
index 490a008dfcb..96c1e9830fb 100644
--- a/src/xselect.c
+++ b/src/xselect.c
@@ -2522,7 +2522,8 @@ FRAME is on.  If FRAME is nil, the selected frame is used.  */)
 
 bool
 x_handle_dnd_message (struct frame *f, const XClientMessageEvent *event,
-                      struct x_display_info *dpyinfo, struct input_event *bufp)
+                      struct x_display_info *dpyinfo, struct input_event *bufp,
+		      bool root_window_coords, int root_x, int root_y)
 {
   Lisp_Object vec;
   Lisp_Object frame;
@@ -2532,6 +2533,7 @@ x_handle_dnd_message (struct frame *f, const XClientMessageEvent *event,
   unsigned char *data = (unsigned char *) event->data.b;
   int idata[5];
   ptrdiff_t i;
+  Window child_return;
 
   for (i = 0; i < dpyinfo->x_dnd_atoms_length; ++i)
     if (dpyinfo->x_dnd_atoms[i] == event->message_type) break;
@@ -2563,7 +2565,15 @@ x_handle_dnd_message (struct frame *f, const XClientMessageEvent *event,
 					 event->format,
 					 size));
 
-  x_relative_mouse_position (f, &x, &y);
+  if (!root_window_coords)
+    x_relative_mouse_position (f, &x, &y);
+  else
+    XTranslateCoordinates (dpyinfo->display,
+			   dpyinfo->root_window,
+			   FRAME_X_WINDOW (f),
+			   root_x, root_y,
+			   &x, &y, &child_return);
+
   bufp->kind = DRAG_N_DROP_EVENT;
   bufp->frame_or_window = frame;
   bufp->timestamp = CurrentTime;
diff --git a/src/xterm.c b/src/xterm.c
index d9dd29ca128..d79871e0210 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -15762,6 +15762,31 @@ x_monitors_changed_cb (GdkScreen *gscr, gpointer user_data)
 }
 #endif
 
+/* Extract the root window coordinates from the client message EVENT
+   if it is a message that we already understand.  Return false if the
+   event was not understood.  */
+static bool
+x_coords_from_dnd_message (struct x_display_info *dpyinfo,
+			   XEvent *event, int *x_out, int *y_out)
+{
+  if (event->type != ClientMessage)
+    return false;
+
+  if (event->xclient.message_type == dpyinfo->Xatom_XdndPosition)
+    {
+      if (event->xclient.format != 32)
+	return false;
+
+      *x_out = (((unsigned long) event->xclient.data.l[2]) >> 16
+		& 0xffff);
+      *y_out = (event->xclient.data.l[2] & 0xffff);
+
+      return true;
+    }
+
+  return false;
+}
+
 /* Handles the XEvent EVENT on display DPYINFO.
 
    *FINISH is X_EVENT_GOTO_OUT if caller should stop reading events.
@@ -15804,6 +15829,7 @@ handle_one_xevent (struct x_display_info *dpyinfo,
   GdkEvent *copy = NULL;
   GdkDisplay *gdpy = gdk_x11_lookup_xdisplay (dpyinfo->display);
 #endif
+  int dx, dy;
   USE_SAFE_ALLOCA;
 
   *finish = X_EVENT_NORMAL;
@@ -15835,6 +15861,8 @@ handle_one_xevent (struct x_display_info *dpyinfo,
     {
     case ClientMessage:
       {
+	int rc;
+
 	if (x_dnd_in_progress
 	    && FRAME_DISPLAY_INFO (x_dnd_frame) == dpyinfo
 	    && event->xclient.message_type == dpyinfo->Xatom_XdndStatus)
@@ -16211,7 +16239,17 @@ handle_one_xevent (struct x_display_info *dpyinfo,
 	f = any;
 	if (!f)
 	  goto OTHER;
-	if (x_handle_dnd_message (f, &event->xclient, dpyinfo, &inev.ie))
+
+	/* These values are always used initialized, but GCC doesn't
+	   know that.  */
+	dx = 0;
+	dy = 0;
+
+	rc = x_coords_from_dnd_message (dpyinfo, (XEvent *) event,
+					&dx, &dy);
+
+	if (x_handle_dnd_message (f, &event->xclient, dpyinfo, &inev.ie,
+				  rc, dx, dy))
 	  *finish = X_EVENT_DROP;
       }
       break;
diff --git a/src/xterm.h b/src/xterm.h
index 25c2453ee78..82b4308041a 100644
--- a/src/xterm.h
+++ b/src/xterm.h
@@ -1540,7 +1540,8 @@ extern Lisp_Object x_atom_to_symbol (struct x_display_info *, Atom);
 extern bool x_handle_dnd_message (struct frame *,
 				  const XClientMessageEvent *,
 				  struct x_display_info *,
-				  struct input_event *);
+				  struct input_event *,
+				  bool, int, int);
 extern int x_check_property_data (Lisp_Object);
 extern void x_fill_property_data (Display *,
                                   Lisp_Object,
-- 
2.39.2