From 4d17c5ab27be6adb8437d7a685b1a9f8fee0ade5 Mon Sep 17 00:00:00 2001
From: Jared Finder <jared@finder.org>
Date: Sat, 4 Jan 2025 13:55:05 -0800
Subject: [PATCH] Support TTY child frames with GPM mouse

* src/term.c (frame_at): New C function, wraps Lisp `frame-at'.
(handle_one_term_event): Call frame_at to get frame under mouse,
store it in last_mouse_frame.  Alter event coordinates based on
mouse frame.
(term_mouse_position): Use last_mouse_frame when it is set.
(syms_of_term): Add Qframe_at.
* src/termhooks.h: Make Gpm_Event parameter const.
---
 src/term.c      | 52 +++++++++++++++++++++++++++++++++++++------------
 src/termhooks.h |  2 +-
 2 files changed, 41 insertions(+), 13 deletions(-)

diff --git a/src/term.c b/src/term.c
index 368e20803e1..bbf0bafb93f 100644
--- a/src/term.c
+++ b/src/term.c
@@ -141,6 +141,7 @@ #define OUTPUT1_IF(tty, a) \
 struct tty_display_info *gpm_tty = NULL;
 
 /* Last recorded mouse coordinates.  */
+static Lisp_Object last_mouse_frame;
 static int last_mouse_x, last_mouse_y;
 #endif /* HAVE_GPM */
 
@@ -2638,7 +2639,11 @@ term_mouse_position (struct frame **fp, int insist, Lisp_Object *bar_window,
 		     enum scroll_bar_part *part, Lisp_Object *x,
 		     Lisp_Object *y, Time *timeptr)
 {
-  *fp = SELECTED_FRAME ();
+  /* This code runs even when `gpm-mouse-mode' was never active, like
+     inside an xterm.  In such cases, last_mouse_frame will never be
+     set, so fallback to SELECTED_FRAME. */
+  *fp = FRAMEP (last_mouse_frame) ? XFRAME (last_mouse_frame)
+    : SELECTED_FRAME ();
   (*fp)->mouse_moved = 0;
 
   *bar_window = Qnil;
@@ -2712,10 +2717,28 @@ term_mouse_click (struct input_event *result, Gpm_Event *event,
   return Qnil;
 }
 
+static Lisp_Object
+frame_at(int x, int y)
+{
+  Lisp_Object frame = CALLN (Ffuncall, Qframe_at,
+			     make_fixnum (x), make_fixnum (y));
+  if (NILP (frame))
+    {
+      frame = selected_frame;
+    }
+
+  return frame;
+}
+
 int
-handle_one_term_event (struct tty_display_info *tty, Gpm_Event *event)
+handle_one_term_event (struct tty_display_info *tty, const Gpm_Event *event_in)
 {
-  struct frame *f = XFRAME (tty->top_frame);
+  Lisp_Object frame = frame_at(event_in->x, event_in->y);
+  struct frame *f = XFRAME (frame);
+  Gpm_Event event = *event_in;
+  event.x -= f->left_pos;
+  event.y -= f->top_pos;
+
   struct input_event ie;
   int count = 0;
 
@@ -2723,30 +2746,34 @@ handle_one_term_event (struct tty_display_info *tty, Gpm_Event *event)
   ie.kind = NO_EVENT;
   ie.arg = Qnil;
 
-  if (event->type & (GPM_MOVE | GPM_DRAG))
+  if (event.type & (GPM_MOVE | GPM_DRAG))
     {
-      Gpm_DrawPointer (event->x, event->y, fileno (tty->output));
+      /* The pointer must be drawn using screen coordinates (x,y), not
+	 frame coordinates. Use event_in which has an unmodified event
+	 directly from GPM. */
+      Gpm_DrawPointer (event_in->x, event_in->y, fileno (tty->output));
 
       /* Has the mouse moved off the glyph it was on at the last
          sighting?  */
-      if (event->x != last_mouse_x || event->y != last_mouse_y)
+      if (event.x != last_mouse_x || event.y != last_mouse_y)
         {
-          /* FIXME: These three lines can not be moved into
+          /* FIXME: These four lines can not be moved into
              update_mouse_position unless xterm-mouse gets updated to
              generate mouse events via C code.  See
              https://lists.gnu.org/archive/html/emacs-devel/2020-11/msg00163.html */
-          last_mouse_x = event->x;
-          last_mouse_y = event->y;
+          last_mouse_frame = frame;
+          last_mouse_x = event.x;
+          last_mouse_y = event.y;
           f->mouse_moved = 1;
 
-          count += update_mouse_position (f, event->x, event->y);
+          count += update_mouse_position (f, event.x, event.y);
         }
     }
   else
     {
       f->mouse_moved = 0;
-      term_mouse_click (&ie, event, f);
-      ie.arg = tty_handle_tab_bar_click (f, event->x, event->y,
+      term_mouse_click (&ie, &event, f);
+      ie.arg = tty_handle_tab_bar_click (f, event.x, event.y,
 					 (ie.modifiers & down_modifier) != 0, &ie);
       kbd_buffer_store_event (&ie);
       count++;
@@ -4970,6 +4997,7 @@ syms_of_term (void)
 #ifdef HAVE_GPM
   defsubr (&Sgpm_mouse_start);
   defsubr (&Sgpm_mouse_stop);
+  DEFSYM (Qframe_at, "frame-at");
 #endif /* HAVE_GPM */
 
   defsubr (&Stty_frame_geometry);
diff --git a/src/termhooks.h b/src/termhooks.h
index b32804a57b3..0795148f1af 100644
--- a/src/termhooks.h
+++ b/src/termhooks.h
@@ -458,7 +458,7 @@ #define EVENT_INIT(event) (memset (&(event), 0, sizeof (struct input_event)), \
 
 #ifdef HAVE_GPM
 #include <gpm.h>
-extern int handle_one_term_event (struct tty_display_info *, Gpm_Event *);
+extern int handle_one_term_event (struct tty_display_info *, const Gpm_Event *);
 extern void term_mouse_moveto (int, int);
 
 /* The device for which we have enabled gpm support.  */
-- 
2.39.5