bug#3468: drag and drop text

bug#3468: drag and drop text

[Erdkern Erdkern]

I use windows as operating system. I want to drag text from text editor or browser (say Wordpad or Firefox) and drop it in emacs, but this is not possible, drop is not allowed. On the other side, if I drag an unknown filetype (say, an *.rdp-File) into emacs, it is dropped as text. 

In GNU Emacs 22.3.1 (i386-mingw-nt5.1.2600)
 of 2008-09-06 on SOFT-MJASON
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4)'

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: DEU
  locale-coding-system: cp1252
  default-enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  cua-mode: t
  encoded-kbd-mode: t
  tooltip-mode: t
  tool-bar-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  unify-8859-on-encoding-mode: t
  utf-translate-cjk-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <down> 
<down-mouse-1> <mouse-1> <down-mouse-1> <mouse-1> <down-mouse-1> 
<mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> 
<mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> <mouse-1> 
<mouse-1> <mouse-1> <mouse-1> <mouse-1> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <tool-bar> 
<kill-buffer> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<menu-bar> <help-menu> <send-emacs-bug-report>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Loading emacsbug...
Loading regexp-opt...done
Loading emacsbug...done
Loading help-mode...done
Auto-saving...done
Undo! [29 times]
Auto-saving...done
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bug#3468: drag and drop text

[Lars Ingebrigtsen]

"Erdkern Erdkern" <Erdkern2000@gmx.de> writes:

> I use windows as operating system. I want to drag text from text
> editor or browser (say Wordpad or Firefox) and drop it in emacs, but
> this is not possible, drop is not allowed. On the other side, if I
> drag an unknown filetype (say, an *.rdp-File) into emacs, it is
> dropped as text.

(I'm going through old bug reports that unfortunately didn't get any
response at the time.)

I tried this in Emacs 27, but on GNU/Linux, and it worked fine for me
there.  Are you still seeing this problem?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#3468: drag and drop text

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Mon, 30 Sep 2019 17:29:54 +0200
> Cc: 3468@debbugs.gnu.org
> 
> I tried this in Emacs 27, but on GNU/Linux, and it worked fine for me
> there.  Are you still seeing this problem?

Emacs on MS-Windows doesn't support drag-n-drop of arbitrary text, it
only supports drag-n-drop of file names.  This is indicated by the
"you can't do that" icon shown as the mouse pointer when you attempt
to drop the text onto the Emacs frame.

The Emacs User manual says in "Drag and Drop":

     The XDND and Motif drag and drop protocols, and the old KDE 1.x
  protocol, are currently supported.

which doesn't include any MS-Windows protocols.

The reason for not supporting this on MS-Windows is that the relevant
system APIs are only available for C++ programs.  If someone knows how
to work around this limitation, I'm sure we will welcome patches or at
least an explanation for how to do that in plain C.

bug#3468: drag and drop text

[Cecilio Pardo]

[-- Attachment #1: Type: text/plain, Size: 428 bytes --]

This patch implements drag-and-drop for w32 for files and text, using C,
not C++.
This should work from Windows 95, but I can't test it.  Because of this,
the prior implementation with WM_DROPFILES has been removed with '#if
0', and can probably be completely removed.

I tested with mingw-w64 and mingw on Windows 11.

Text is inserted at point position, not at drop position.  I don't know
how this works on other platforms.


[-- Attachment #2: 0001-Implement-drag-n-drop-for-w32-with-support-for-files.patch --]
[-- Type: text/plain, Size: 13699 bytes --]

From 1712ab3ba109b2beafa418f0b12d09c836590b2c Mon Sep 17 00:00:00 2001
From: Cecilio Pardo <cpardo@imayhem.com>
Date: Fri, 27 Sep 2024 23:58:02 +0200
Subject: [PATCH] Implement drag-n-drop for w32 with support for files and text

Implement dnd with IDropTarget

* lisp/term/w32-win.el (w32-drag-n-drop): changed to handle files or strings
* src/w32fns.c
(process_dropfiles): new, convert DROPFILES struct to array of strings
(w32_createwindow): assign an IDropTarget to each new frame
(w32_name_of_message): added new messages
(w32_msg_pump): Changed CoInitialize to OleInitialize, needed by the
drag-n-drop functions
(w32_wnd_proc): new struct w32_drop_target, and w32_drop_target_*
functions to implement the IDropTarget interface
* src/w32term.c (w32_read_socket): handle WM_EMACS_DROPFILES,
WM_EMACS_DROPSTRING, skip WM_EMACS_DROPFILES
* src/w32term.h (): add WM_EMACS_DROPFILES, WM_EMACS_DROPSTRING
---
 lisp/term/w32-win.el |  19 ++--
 src/w32fns.c         | 202 ++++++++++++++++++++++++++++++++++++++++++-
 src/w32term.c        |  46 ++++++++++
 src/w32term.h        |   4 +-
 4 files changed, 260 insertions(+), 11 deletions(-)

diff --git a/lisp/term/w32-win.el b/lisp/term/w32-win.el
index b57b3dd3bef..ac85ec8d945 100644
--- a/lisp/term/w32-win.el
+++ b/lisp/term/w32-win.el
@@ -131,8 +131,11 @@ w32-dropped-file-to-url
    file-name))
 
 (defun w32-drag-n-drop (event &optional new-frame)
-  "Edit the files listed in the drag-n-drop EVENT.
-Switch to a buffer editing the last file dropped."
+  "If the drag-n-drop EVENT is for a file or files, edit those
+files. Switch to a buffer editing the last file dropped.
+
+If the EVENT is for text, insert the text at point on the buffer shown
+in the target window, or add to kill ring if that buffer is read-only."
   (interactive "e")
   (save-excursion
     ;; Make sure the drop target has positive co-ords
@@ -140,6 +143,7 @@ w32-drag-n-drop
     ;; won't work.  <skx@tardis.ed.ac.uk>
     (let* ((window (posn-window (event-start event)))
 	   (coords (posn-x-y (event-start event)))
+           (arg (car (cdr (cdr event))))
 	   (x (car coords))
 	   (y (cdr coords)))
       (if (and (> x 0) (> y 0))
@@ -150,11 +154,12 @@ w32-drag-n-drop
       (raise-frame)
       (setq window (selected-window))
 
-      (dnd-handle-multiple-urls
-       window
-       (mapcar #'w32-dropped-file-to-url
-               (car (cdr (cdr event))))
-       'private))))
+      (if (stringp arg)
+          (dnd-insert-text window 'copy arg)
+        (dnd-handle-multiple-urls
+         window
+         (mapcar #'w32-dropped-file-to-url arg)
+         'private)))))
 
 (defun w32-drag-n-drop-other-frame (event)
   "Edit the files listed in the drag-n-drop EVENT, in other frames.
diff --git a/src/w32fns.c b/src/w32fns.c
index 0a3f5c38a58..fdba3524846 100644
--- a/src/w32fns.c
+++ b/src/w32fns.c
@@ -34,6 +34,12 @@ #define _WIN32_WINNT 0x0600
 
 #include <c-ctype.h>
 
+#define COBJMACROS /* Ask for C definitions for COM.  */
+#include <shlobj.h>
+#include <oleidl.h>
+#include <objidl.h>
+#include <ole2.h>
+
 #include "lisp.h"
 #include "w32term.h"
 #include "frame.h"
@@ -359,6 +365,10 @@ #define WS_EX_NOACTIVATE 0x08000000L
 
 static struct w32_display_info *w32_display_info_for_name (Lisp_Object);
 
+static void my_post_msg (W32Msg*, HWND, UINT, WPARAM, LPARAM);
+static unsigned int w32_get_modifiers (void);
+
+
 /* Let the user specify a display with a frame.
    nil stands for the selected frame--or, if that is not a w32 frame,
    the first display on the list.  */
@@ -2464,6 +2474,168 @@ w32_createhscrollbar (struct frame *f, struct scroll_bar * bar)
   return hwnd;
 }
 
+/* From the DROPFILES struct, extract the list of filenames.  Returns a
+   NULL terminated malloc array of malloc strings that should be freed
+   by the caller.  */
+static char **
+process_dropfiles (DROPFILES *files)
+{
+  char *start_of_files = (char*)files + files->pFiles;
+  int count = 0;
+  char filename[MAX_PATH];
+  char **filenames;
+
+  if (files->fWide)
+    {
+      WCHAR *p = (WCHAR*)start_of_files;
+      for ( ; *p; count ++, p += wcslen (p) + 1)
+	;
+      filenames = malloc ((count+1) * sizeof (char*));
+      filenames [count] = NULL;
+      p = (WCHAR*)start_of_files;
+      for ( int i = 0; *p; p += wcslen (p) + 1, i++)
+	{
+	  filename_from_utf16 (p, filename);
+	  filenames [i] = xstrdup (filename);
+	}
+    }
+  else
+    {
+      char *p = start_of_files;
+      for ( ; *p; count ++, p += strlen (p) + 1)
+	;
+      filenames = malloc ((count + 1) * sizeof (char*));
+      filenames [count] = NULL;
+      p = start_of_files;
+      for ( int i = 0; *p; p += strlen(p) + 1, i++)
+	{
+	  filename_from_ansi (p, filename);
+	  filenames[i] = xstrdup (filename);
+	}
+    }
+  return filenames;
+}
+
+struct w32_drop_target {
+  /* i_drop_target must be the first member.  */
+  IDropTarget i_drop_target;
+  HWND hwnd;
+};
+
+static HRESULT STDMETHODCALLTYPE
+w32_drop_target_QueryInterface (IDropTarget *t, REFIID ri, void **r)
+{
+  return E_NOINTERFACE;
+}
+
+static ULONG STDMETHODCALLTYPE
+w32_drop_target_AddRef (IDropTarget *This)
+{
+  return 1;
+}
+
+static ULONG STDMETHODCALLTYPE
+w32_drop_target_Release (IDropTarget *This)
+{
+  struct w32_drop_target *target = (struct w32_drop_target *)This;
+  xfree( target->i_drop_target.lpVtbl );
+  xfree( target );
+  return 0;
+}
+
+static HRESULT STDMETHODCALLTYPE
+w32_drop_target_DragEnter( IDropTarget *This, IDataObject *pDataObj, DWORD grfKeyState, POINTL pt, DWORD *pdwEffect)
+{
+  *pdwEffect = DROPEFFECT_COPY;
+  return S_OK;
+}
+
+static HRESULT STDMETHODCALLTYPE
+w32_drop_target_DragOver ( IDropTarget *This, DWORD grfKeyState, POINTL pt, DWORD *pdwEffect)
+{
+  *pdwEffect = DROPEFFECT_COPY;
+  return S_OK;
+}
+
+static HRESULT STDMETHODCALLTYPE
+w32_drop_target_DragLeave( IDropTarget *This )
+{
+  return S_OK;
+}
+
+static HRESULT STDMETHODCALLTYPE
+w32_drop_target_Drop (IDropTarget *This, IDataObject *pDataObj,
+		      DWORD grfKeyState, POINTL pt, DWORD *pdwEffect)
+{
+  struct w32_drop_target *target = (struct w32_drop_target *)This;
+  *pdwEffect = DROPEFFECT_COPY;
+
+  W32Msg msg = {0};
+  msg.dwModifiers = w32_get_modifiers();
+  msg.msg.time = GetMessageTime ();
+  msg.msg.pt.x = pt.x;
+  msg.msg.pt.y = pt.y;
+
+  STGMEDIUM stgmedium;
+
+  /* Try for dropped files (CF_HDROP).  */
+  FORMATETC formatetc = { CF_HDROP, NULL, DVASPECT_CONTENT, -1, TYMED_HGLOBAL };
+  if (SUCCEEDED (IDataObject_GetData (pDataObj, &formatetc, &stgmedium)))
+    {
+      if (stgmedium.tymed == TYMED_HGLOBAL)
+	{
+	  DROPFILES *files = (DROPFILES*)GlobalLock (stgmedium.hGlobal);
+	  if (files)
+	      my_post_msg (&msg, target->hwnd, WM_EMACS_DROPFILES,
+			   0, (LPARAM)process_dropfiles (files) );
+	  GlobalUnlock (stgmedium.hGlobal);
+	}
+      ReleaseStgMedium (&stgmedium);
+      return S_OK;
+    }
+
+  formatetc.cfFormat = CF_UNICODETEXT;
+  if (SUCCEEDED (IDataObject_GetData (pDataObj, &formatetc, &stgmedium)))
+    {
+      if (stgmedium.tymed == TYMED_HGLOBAL)
+	{
+	  WCHAR *text = (WCHAR*)GlobalLock (stgmedium.hGlobal);
+	  Lisp_Object text_string = from_unicode_buffer (text);
+	  char *utf8 = xstrdup (SSDATA (ENCODE_UTF_8 (text_string)));
+	  my_post_msg (&msg, target->hwnd, WM_EMACS_DROPSTRING,
+		       0, (LPARAM)utf8 );
+	  GlobalUnlock (stgmedium.hGlobal);
+	}
+      ReleaseStgMedium (&stgmedium);
+      return S_OK;
+    }
+
+  formatetc.cfFormat = CF_TEXT;
+  if (SUCCEEDED (IDataObject_GetData (pDataObj, &formatetc, &stgmedium)))
+    {
+      if (stgmedium.tymed == TYMED_HGLOBAL)
+	{
+	  char *text = (char*)GlobalLock (stgmedium.hGlobal);
+
+	  int l = strlen (text);
+	  WCHAR *text_utf16 = xmalloc (sizeof (WCHAR) * l + 1 );;
+	  if (MultiByteToWideChar (CP_ACP, 0, text, l, text_utf16, l + 1))
+	    {
+	      Lisp_Object text_string = from_unicode_buffer (text_utf16);
+	      char *utf8 = xstrdup (SSDATA (ENCODE_UTF_8 (text_string)));
+	      my_post_msg (&msg, target->hwnd, WM_EMACS_DROPSTRING,
+			   0, (LPARAM)utf8 );
+	    }
+	  xfree (text_utf16);
+	  GlobalUnlock (stgmedium.hGlobal);
+	}
+      ReleaseStgMedium (&stgmedium);
+      return S_OK;
+    }
+
+  return S_OK;
+}
+
 static void
 w32_createwindow (struct frame *f, int *coords)
 {
@@ -2548,7 +2720,23 @@ w32_createwindow (struct frame *f, int *coords)
       SetWindowLong (hwnd, WND_BACKGROUND_INDEX, FRAME_BACKGROUND_PIXEL (f));
 
       /* Enable drag-n-drop.  */
+      struct w32_drop_target *drop_target = xmalloc (sizeof (struct w32_drop_target));
+      drop_target-> hwnd = hwnd;
+
+      IDropTargetVtbl *vtbl = xmalloc (sizeof (IDropTargetVtbl));
+      drop_target->i_drop_target.lpVtbl = vtbl;
+      vtbl->QueryInterface = w32_drop_target_QueryInterface;
+      vtbl->AddRef = w32_drop_target_AddRef;
+      vtbl->Release = w32_drop_target_Release;
+      vtbl->DragEnter = w32_drop_target_DragEnter;
+      vtbl->DragOver = w32_drop_target_DragOver;
+      vtbl->DragLeave = w32_drop_target_DragLeave;
+      vtbl->Drop = w32_drop_target_Drop;
+      RegisterDragDrop (hwnd, &drop_target->i_drop_target);
+
+#if 0
       DragAcceptFiles (hwnd, TRUE);
+#endif
 
       /* Enable system light/dark theme.  */
       w32_applytheme (hwnd);
@@ -3399,6 +3587,8 @@ #define M(msg) { msg, # msg }
       M (WM_EMACS_PAINT),
       M (WM_EMACS_IME_STATUS),
       M (WM_CHAR),
+      M (WM_EMACS_DROPFILES),
+      M (WM_EMACS_DROPSTRING),
 #undef M
       { 0, 0 }
   };
@@ -3465,13 +3655,14 @@ w32_msg_pump (deferred_msg * msg_buf)
 	      /* Produced by complete_deferred_msg; just ignore.  */
 	      break;
 	    case WM_EMACS_CREATEWINDOW:
-	      /* Initialize COM for this window. Even though we don't use it,
-		 some third party shell extensions can cause it to be used in
+	      /* Initialize COM for this window. Needed for RegisterDragDrop.
+		 Some third party shell extensions can cause it to be used in
 		 system dialogs, which causes a crash if it is not initialized.
 		 This is a known bug in Windows, which was fixed long ago, but
 		 the patch for XP is not publicly available until XP SP3,
 		 and older versions will never be patched.  */
-	      CoInitialize (NULL);
+	      OleInitialize (NULL);
+
 	      w32_createwindow ((struct frame *) msg.wParam,
 				(int *) msg.lParam);
 	      if (!PostThreadMessage (dwMainThreadId, WM_EMACS_DONE, 0, 0))
@@ -5106,7 +5297,9 @@ #define MOUSEEVENTF_FROMTOUCH 0xFF515700
       return 0;
 
     case WM_MOUSEWHEEL:
+#if 0
     case WM_DROPFILES:
+#endif
       wmsg.dwModifiers = w32_get_modifiers ();
       my_post_msg (&wmsg, hwnd, msg, wParam, lParam);
       signal_user_input ();
@@ -5597,7 +5790,10 @@ #define WM_TOUCH 576
       }
 
     case WM_EMACS_DESTROYWINDOW:
+	RevokeDragDrop ((HWND) wParam);
+#if 0
       DragAcceptFiles ((HWND) wParam, FALSE);
+#endif
       return DestroyWindow ((HWND) wParam);
 
     case WM_EMACS_HIDE_CARET:
diff --git a/src/w32term.c b/src/w32term.c
index 62037e3b2cd..e1ff4112a7b 100644
--- a/src/w32term.c
+++ b/src/w32term.c
@@ -3576,6 +3576,7 @@ w32_construct_mouse_wheel (struct input_event *result, W32Msg *msg,
   return Qnil;
 }
 
+#if 0
 static Lisp_Object
 w32_construct_drag_n_drop (struct input_event *result, W32Msg *msg,
                            struct frame *f)
@@ -3651,6 +3652,7 @@ w32_construct_drag_n_drop (struct input_event *result, W32Msg *msg,
   return Qnil;
 }
 
+#endif
 \f
 #if HAVE_W32NOTIFY
 
@@ -5682,12 +5684,56 @@ w32_read_socket (struct terminal *terminal,
 	  }
 	  break;
 
+#if 0
 	case WM_DROPFILES:
 	  f = w32_window_to_frame (dpyinfo, msg.msg.hwnd);
 
 	  if (f)
 	    w32_construct_drag_n_drop (&inev, &msg, f);
 	  break;
+#endif
+
+	case WM_EMACS_DROPSTRING:
+	    f = w32_window_to_frame (dpyinfo, msg.msg.hwnd);
+	    if (!f)
+	      break;
+	    XSETFRAME (inev.frame_or_window, f);
+	    inev.kind = DRAG_N_DROP_EVENT;
+	    inev.code = 0;
+	    inev.timestamp = msg.msg.time;
+	    inev.modifiers = msg.dwModifiers;
+	    ScreenToClient (msg.msg.hwnd, &msg.msg.pt);
+	    XSETINT (inev.x, msg.msg.pt.x);
+	    XSETINT (inev.y, msg.msg.pt.y);
+	    inev.arg = make_string ((char*)msg.msg.lParam, strlen((char*)msg.msg.lParam));
+	    xfree ((void*)msg.msg.lParam);
+	    break;
+
+	case WM_EMACS_DROPFILES:
+	  {
+	    f = w32_window_to_frame (dpyinfo, msg.msg.hwnd);
+	    if (!f)
+	      break;
+	    XSETFRAME (inev.frame_or_window, f);
+	    inev.kind = DRAG_N_DROP_EVENT;
+	    inev.code = 0;
+	    inev.timestamp = msg.msg.time;
+	    inev.modifiers = msg.dwModifiers;
+	    ScreenToClient (msg.msg.hwnd, &msg.msg.pt);
+	    XSETINT (inev.x, msg.msg.pt.x);
+	    XSETINT (inev.y, msg.msg.pt.y);
+
+	    Lisp_Object files = Qnil;
+	    char **filenames = (char**)msg.msg.lParam;
+	    for (int n = 0; filenames[n]; n++ )
+	      {
+		files = Fcons (DECODE_FILE (build_string (filenames[n])), files );
+		xfree (filenames[n]);
+	      }
+	    xfree (filenames);
+	    inev.arg = files;
+	    break;
+	  }
 
 	case WM_HSCROLL:
 	  {
diff --git a/src/w32term.h b/src/w32term.h
index 47be542f570..c1253af47c4 100644
--- a/src/w32term.h
+++ b/src/w32term.h
@@ -710,7 +710,9 @@ #define WM_EMACS_BRINGTOTOP            (WM_EMACS_START + 23)
 #define WM_EMACS_INPUT_READY           (WM_EMACS_START + 24)
 #define WM_EMACS_FILENOTIFY            (WM_EMACS_START + 25)
 #define WM_EMACS_IME_STATUS            (WM_EMACS_START + 26)
-#define WM_EMACS_END                   (WM_EMACS_START + 27)
+#define WM_EMACS_DROPFILES             (WM_EMACS_START + 27)
+#define WM_EMACS_DROPSTRING            (WM_EMACS_START + 28)
+#define WM_EMACS_END                   (WM_EMACS_START + 29)
 
 #define WND_FONTWIDTH_INDEX    (0)
 #define WND_LINEHEIGHT_INDEX   (4)
-- 
2.35.1.windows.2

bug#3468: drag and drop text

[Eli Zaretskii]

> Date: Sat, 28 Sep 2024 23:52:45 +0200
> From: Cecilio Pardo <cpardo@imayhem.com>
> 
> This patch implements drag-and-drop for w32 for files and text, using C,
> not C++.
> This should work from Windows 95, but I can't test it.  Because of this,
> the prior implementation with WM_DROPFILES has been removed with '#if
> 0', and can probably be completely removed.

I think we should remove those "#if 0" parts, yes.  If and when
someone is able to test this on Windows 9X, they will report problems
they encounter, and we can take it from there.  The removed code is
available in Git, so it is not lost.

> Text is inserted at point position, not at drop position.  I don't know
> how this works on other platforms.

Po Lu, any comments to this particular aspect?

I have some comments to the code below.

> Implement dnd with IDropTarget

This should explicitly mention MS-Windows.

> * lisp/term/w32-win.el (w32-drag-n-drop): changed to handle files or strings
> * src/w32fns.c
> (process_dropfiles): new, convert DROPFILES struct to array of strings
> (w32_createwindow): assign an IDropTarget to each new frame
> (w32_name_of_message): added new messages
> (w32_msg_pump): Changed CoInitialize to OleInitialize, needed by the
> drag-n-drop functions
> (w32_wnd_proc): new struct w32_drop_target, and w32_drop_target_*
> functions to implement the IDropTarget interface
> * src/w32term.c (w32_read_socket): handle WM_EMACS_DROPFILES,
> WM_EMACS_DROPSTRING, skip WM_EMACS_DROPFILES
> * src/w32term.h (): add WM_EMACS_DROPFILES, WM_EMACS_DROPSTRING

Some of these lines are too long (try limiting to 64 columns).  Also,
descriptions of changes should be complete sentences: start with a
capital letter and end in a period, like this:

 (w32_createwindow): Assign an IDropTarget to each new frame.

>  (defun w32-drag-n-drop (event &optional new-frame)
> -  "Edit the files listed in the drag-n-drop EVENT.
> -Switch to a buffer editing the last file dropped."
> +  "If the drag-n-drop EVENT is for a file or files, edit those
> +files. Switch to a buffer editing the last file dropped.

The first line of a doc string should be a single complete sentence.
In this case, I suggest:

    Perform drag-n-drop action according to data in EVENT.
  If EVENT is for one or more files, visit those files in corresponding
  buffers, and switch to the buffer that visits the last dropped file.
  If EVENT is for text, insert that text at point into the buffer
  shown in the window that is the target of the drop; if that buffer is
  read-only, add the dropped text to kill-ring.
  If the optional argument NEW-FRAME is non-nil, perform the
  drag-n-drop action in a newly-created frame using its selected-window
  and that window's buffer.

> +      (if (stringp arg)
> +          (dnd-insert-text window 'copy arg)
> +        (dnd-handle-multiple-urls
> +         window
> +         (mapcar #'w32-dropped-file-to-url arg)
> +         'private)))))

Please add a comment here saying that the payload in the EVENT should
be either a string (meaning the text to drop) or a list of strings
(meaning names of files to drop).  This is important because a file
name is also a string, so it is not obvious how we distinguish between
the two possible payloads.

> +/* From the DROPFILES struct, extract the list of filenames.  Returns a
> +   NULL terminated malloc array of malloc strings that should be freed
                      ^^^^^^          ^^^^^^
"malloced"

> +static char **
> +process_dropfiles (DROPFILES *files)
> +{
> +  char *start_of_files = (char*)files + files->pFiles;
                            ^^^^^^^^^^^^
Style: "(char *) files".

> +  int count = 0;
> +  char filename[MAX_PATH];
                   ^^^^^^^^
This should be MAX_UTF8_PATH, since filename[] is UTF-8 encoded.

> +  if (files->fWide)

What determines whether we get "wide" file names or ANSI file names?
We want to get "wide" file names where possible, but I don't see where
we request that?

> +    {
> +      WCHAR *p = (WCHAR*)start_of_files;
                    ^^^^^^^^^^^^^^^^^^^^^^
"(WCHAR *) start_of_files".

> +      p = (WCHAR*)start_of_files;

Likewise.

> +      for ( int i = 0; *p; p += wcslen (p) + 1, i++)
             ^^
Style: no space there.

> +      filenames = malloc ((count+1) * sizeof (char*));

You call malloc here, but the function which frees uses xfree.
We should probably call xmalloc here, but xmalloc could signal an
error, and this code runs in a non-main thread, doesn't it?  If so, I
think the function which frees needs to call 'free', nor 'xfree'.  And
we need to handle the case malloc returns NULL.

> +	  filenames [i] = xstrdup (filename);

For the same reason, we cannot call xstrdup here, and neither can we
call strdup (because it comes from MSVCRT, and will call a different
version of malloc).  We need to provide a private version of strdup.
But see below about moving all this processing to the main thread.

Also, "filenames[i]", without the space before the brackets.

> +  struct w32_drop_target *target = (struct w32_drop_target *)This;
> +  xfree( target->i_drop_target.lpVtbl );
> +  xfree( target );
         ^^^^
Style: missing and extra space again.

> +static HRESULT STDMETHODCALLTYPE
> +w32_drop_target_DragEnter( IDropTarget *This, IDataObject *pDataObj, DWORD grfKeyState, POINTL pt, DWORD *pdwEffect)

Please break this long list of arguments into several lines.
Also, our style is to write

  w32_drop_target_DragEnter (IDropTarget *This,

That is, one space between the function name and the opening
parenthesis, and no space between the parenthesis and the first
argument.

> +static HRESULT STDMETHODCALLTYPE
> +w32_drop_target_DragOver ( IDropTarget *This, DWORD grfKeyState, POINTL pt, DWORD *pdwEffect)

Likewise here (and elsewhere in the patch).

> +  formatetc.cfFormat = CF_UNICODETEXT;
> +  if (SUCCEEDED (IDataObject_GetData (pDataObj, &formatetc, &stgmedium)))
> +    {
> +      if (stgmedium.tymed == TYMED_HGLOBAL)
> +	{
> +	  WCHAR *text = (WCHAR*)GlobalLock (stgmedium.hGlobal);
> +	  Lisp_Object text_string = from_unicode_buffer (text);
> +	  char *utf8 = xstrdup (SSDATA (ENCODE_UTF_8 (text_string)));
> +	  my_post_msg (&msg, target->hwnd, WM_EMACS_DROPSTRING,
> +		       0, (LPARAM)utf8 );
> +	  GlobalUnlock (stgmedium.hGlobal);
> +	}
> +      ReleaseStgMedium (&stgmedium);
> +      return S_OK;
> +    }

If this runs in a non-main thread, then we cannot do this: calling
functions that manipulate Lisp data in non-main threads is a no-no.
Can we instead delegate the actual processing to where
WM_EMACS_DROPSTRING is processed?  If not, why not?

To tell the truth, I'd be happier if we could do the same with
WM_EMACS_DROPFILES, i.e. convert the file names and allocate memory
for them in the main thread: that would remove all the issues
mentioned above with xmalloc, xstrdup, etc., and be in general much
safer.

Also, there's no need to call ENCODE_UTF_8, since from_unicode_buffer
already returns the text in the internal representation.  You are
basically decoding strings from UTF-16, then encode them in UTF-8,
only to decode them again in the main thread.  (This will also be
avoided if we do everything in the main thread.)

> +  formatetc.cfFormat = CF_TEXT;
> +  if (SUCCEEDED (IDataObject_GetData (pDataObj, &formatetc, &stgmedium)))
> +    {
> +      if (stgmedium.tymed == TYMED_HGLOBAL)
> +	{
> +	  char *text = (char*)GlobalLock (stgmedium.hGlobal);
> +
> +	  int l = strlen (text);
> +	  WCHAR *text_utf16 = xmalloc (sizeof (WCHAR) * l + 1 );;
> +	  if (MultiByteToWideChar (CP_ACP, 0, text, l, text_utf16, l + 1))

We cannot call MultiByteToWideChar directly: it will prevent Emacs
from running on Windows 9X, where that function is available only
after loading a special DLL.  We need to call this function via a
function pointer, pMultiByteToWideChar.

> +	    {
> +	      Lisp_Object text_string = from_unicode_buffer (text_utf16);
> +	      char *utf8 = xstrdup (SSDATA (ENCODE_UTF_8 (text_string)));
> +	      my_post_msg (&msg, target->hwnd, WM_EMACS_DROPSTRING,
> +			   0, (LPARAM)utf8 );

This is a very convoluted way of converting ANSI encoded string to
UTF-8.  I would simply use DECODE_SYSTEM here (subject to the same
restriction regarding doing that in a non-main thread).

> @@ -2548,7 +2720,23 @@ w32_createwindow (struct frame *f, int *coords)
>        SetWindowLong (hwnd, WND_BACKGROUND_INDEX, FRAME_BACKGROUND_PIXEL (f));
>  
>        /* Enable drag-n-drop.  */
> +      struct w32_drop_target *drop_target = xmalloc (sizeof (struct w32_drop_target));
> +      drop_target-> hwnd = hwnd;
> +
> +      IDropTargetVtbl *vtbl = xmalloc (sizeof (IDropTargetVtbl));
                                 ^^^^^^^
w32_createwindow runs in the input thread, so it cannot safely call
xmalloc.

>  	    case WM_EMACS_CREATEWINDOW:
> -	      /* Initialize COM for this window. Even though we don't use it,
> -		 some third party shell extensions can cause it to be used in
> +	      /* Initialize COM for this window. Needed for RegisterDragDrop.
                                               ^^
Two spaces between sentences, please.

> +	case WM_EMACS_DROPSTRING:
> +	    f = w32_window_to_frame (dpyinfo, msg.msg.hwnd);
> +	    if (!f)
> +	      break;
> +	    XSETFRAME (inev.frame_or_window, f);
> +	    inev.kind = DRAG_N_DROP_EVENT;
> +	    inev.code = 0;
> +	    inev.timestamp = msg.msg.time;
> +	    inev.modifiers = msg.dwModifiers;
> +	    ScreenToClient (msg.msg.hwnd, &msg.msg.pt);
> +	    XSETINT (inev.x, msg.msg.pt.x);
> +	    XSETINT (inev.y, msg.msg.pt.y);
> +	    inev.arg = make_string ((char*)msg.msg.lParam, strlen((char*)msg.msg.lParam));

Since we are (hopefully) going to move the prcessing and decoding of
the dropped string to this place, just decoding it from UTF-18 or ANSI
(via DECODE_SYSTEM) should be enough.

> +	    xfree ((void*)msg.msg.lParam);

This may need to be 'free', see above.

> +	case WM_EMACS_DROPFILES:
> +	  {
> +	    f = w32_window_to_frame (dpyinfo, msg.msg.hwnd);
> +	    if (!f)
> +	      break;
> +	    XSETFRAME (inev.frame_or_window, f);
> +	    inev.kind = DRAG_N_DROP_EVENT;
> +	    inev.code = 0;
> +	    inev.timestamp = msg.msg.time;
> +	    inev.modifiers = msg.dwModifiers;
> +	    ScreenToClient (msg.msg.hwnd, &msg.msg.pt);
> +	    XSETINT (inev.x, msg.msg.pt.x);
> +	    XSETINT (inev.y, msg.msg.pt.y);
> +
> +	    Lisp_Object files = Qnil;
> +	    char **filenames = (char**)msg.msg.lParam;
> +	    for (int n = 0; filenames[n]; n++ )
> +	      {
> +		files = Fcons (DECODE_FILE (build_string (filenames[n])), files );
> +		xfree (filenames[n]);
> +	      }
> +	    xfree (filenames);

Similarly here.

Finally, we need a NEWS entry (near the end of NEWS) announcing this
new capability.

Thanks!

bug#3468: drag and drop text

[Cecilio Pardo]

On 29/09/2024 9:19, Eli Zaretskii wrote:

>> +  if (files->fWide)
> 
> What determines whether we get "wide" file names or ANSI file names?
> We want to get "wide" file names where possible, but I don't see where
> we request that?

We can't request it, I suppose it depends on the OS version or the 
program sending the drop.

> If this runs in a non-main thread, then we cannot do this: calling
> functions that manipulate Lisp data in non-main threads is a no-no.
> Can we instead delegate the actual processing to where
> WM_EMACS_DROPSTRING is processed?  If not, why not?

It runs indeed on the "shell thread". I'll move all the processing to 
the message handler.

Thanks a lot for your review, and sorry for all the style mistakes.

bug#3468: drag and drop text

[Eli Zaretskii]

> Date: Sun, 29 Sep 2024 13:17:26 +0200
> Cc: 3468@debbugs.gnu.org
> From: Cecilio Pardo <cpardo@imayhem.com>
> 
> On 29/09/2024 9:19, Eli Zaretskii wrote:
> 
> >> +  if (files->fWide)
> > 
> > What determines whether we get "wide" file names or ANSI file names?
> > We want to get "wide" file names where possible, but I don't see where
> > we request that?
> 
> We can't request it, I suppose it depends on the OS version or the 
> program sending the drop.

What did you see on Windows 11?  Do we always receive "wide" file
names?  Did you try dragging file names whose characters are not
supported by the current ANSI codepage, and if so, did it work?

> > If this runs in a non-main thread, then we cannot do this: calling
> > functions that manipulate Lisp data in non-main threads is a no-no.
> > Can we instead delegate the actual processing to where
> > WM_EMACS_DROPSTRING is processed?  If not, why not?
> 
> It runs indeed on the "shell thread". I'll move all the processing to 
> the message handler.

Thanks.  By "message handler" you mean w32_read_socket, yes?

> Thanks a lot for your review, and sorry for all the style mistakes.

No need to apologize, it takes time to learn the subtleties of our
conventions.

bug#3468: drag and drop text

[Cecilio Pardo]

On 29/09/2024 13:36, Eli Zaretskii wrote:

> What did you see on Windows 11?  Do we always receive "wide" file
> names?  

Yes, always wide on Windows 11 on my tests.

 > Did you try dragging file names whose characters are not supported by 
 > the current ANSI codepage, and if so, did it work?

I just tried and it works fine.

>> It runs indeed on the "shell thread". I'll move all the processing to
>> the message handler.
> 
> Thanks.  By "message handler" you mean w32_read_socket, yes?

Yes.

bug#3468: drag and drop text

[Cecilio Pardo]

[-- Attachment #1: Type: text/plain, Size: 173 bytes --]

Here is the reworked version.

Now the processing of the drop data is delayed until we process the 
WM_EMACS_DROP message at w32_read_socket.

There is no malloc/strdup.




[-- Attachment #2: 0001-Implement-drag-n-drop-for-w32-with-support-for-files.patch --]
[-- Type: text/plain, Size: 15200 bytes --]

From c20e8e3e4880eb65257020ee88298f5697b1dfc3 Mon Sep 17 00:00:00 2001
From: Cecilio Pardo <cpardo@imayhem.com>
Date: Fri, 27 Sep 2024 23:58:02 +0200
Subject: [PATCH] Implement drag-n-drop for w32 with support for files and text

Implement drag-n-drop with IDropTarget for MS-Windows. This
allows for dropping files or text.

* lisp/term/w32-win.el (w32-drag-n-drop): Changed to handle
files or strings.
* src/w32fns.c (process_dropfiles): New function to convert
DROPFILES struct to array of strings.
(w32_process_dnd_data): New function to process drop data.
(w32_try_get_data): Extract data from IDataObject.
(w32_createwindow): Assign an IDropTarget to each new frame.
(w32_name_of_message): Added new message.
(w32_msg_pump): Changed CoInitialize to OleInitialize, needed
by the drag-n-drop functions.
(w32_wnd_proc): New struct w32_drop_target, and
w32_drop_target_* functions to implement the IDropTarget
interface.
* src/w32term.c (w32_read_socket): Handle WM_EMACS_DROP and
remove WM_EMACS_DROPFILES.
* src/w32term.h (): Added new message WM_EMACS_DROP.

..
---
 etc/NEWS             |   5 ++
 lisp/term/w32-win.el |  25 ++++--
 src/w32fns.c         | 203 +++++++++++++++++++++++++++++++++++++++++--
 src/w32term.c        |  98 ++++-----------------
 src/w32term.h        |   4 +-
 5 files changed, 242 insertions(+), 93 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index 37568ffdbea..7c9f6f559ec 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -584,6 +584,11 @@ In particular, it is now possible to show text with embedded newlines in
 a dialog popped by 'message-box'.  This is supported on Windows Vista
 and later versions.
 
+---
+** Emacs on MS-Windows now supports drag-n-drop of text into a buffer.
+This is in addition to drag-n-drop of files, that was already supported.
+
+
 \f
 ----------------------------------------------------------------------
 This file is part of GNU Emacs.
diff --git a/lisp/term/w32-win.el b/lisp/term/w32-win.el
index b57b3dd3bef..541fef2ced3 100644
--- a/lisp/term/w32-win.el
+++ b/lisp/term/w32-win.el
@@ -131,8 +131,15 @@ w32-dropped-file-to-url
    file-name))
 
 (defun w32-drag-n-drop (event &optional new-frame)
-  "Edit the files listed in the drag-n-drop EVENT.
-Switch to a buffer editing the last file dropped."
+  "Perform drag-n-drop action according to data in EVENT.
+If EVENT is for one or more files, visit those files in corresponding
+buffers, and switch to the buffer that visits the last dropped file.
+If EVENT is for text, insert that text at point into the buffer
+shown in the window that is the target of the drop; if that buffer is
+read-only, add the dropped text to kill-ring.
+If the optional argument NEW-FRAME is non-nil, perform the
+drag-n-drop action in a newly-created frame using its selected-window
+and that window's buffer."
   (interactive "e")
   (save-excursion
     ;; Make sure the drop target has positive co-ords
@@ -140,6 +147,7 @@ w32-drag-n-drop
     ;; won't work.  <skx@tardis.ed.ac.uk>
     (let* ((window (posn-window (event-start event)))
 	   (coords (posn-x-y (event-start event)))
+           (arg (car (cdr (cdr event))))
 	   (x (car coords))
 	   (y (cdr coords)))
       (if (and (> x 0) (> y 0))
@@ -150,11 +158,14 @@ w32-drag-n-drop
       (raise-frame)
       (setq window (selected-window))
 
-      (dnd-handle-multiple-urls
-       window
-       (mapcar #'w32-dropped-file-to-url
-               (car (cdr (cdr event))))
-       'private))))
+      ;; arg (the payload of the event) is a string when the drop is
+      ;; text, and a list of strings when the drop is one or more files.
+      (if (stringp arg)
+          (dnd-insert-text window 'copy arg)
+        (dnd-handle-multiple-urls
+         window
+         (mapcar #'w32-dropped-file-to-url arg)
+         'private)))))
 
 (defun w32-drag-n-drop-other-frame (event)
   "Edit the files listed in the drag-n-drop EVENT, in other frames.
diff --git a/src/w32fns.c b/src/w32fns.c
index 0a3f5c38a58..dc69a398019 100644
--- a/src/w32fns.c
+++ b/src/w32fns.c
@@ -34,6 +34,12 @@ #define _WIN32_WINNT 0x0600
 
 #include <c-ctype.h>
 
+#define COBJMACROS /* Ask for C definitions for COM.  */
+#include <shlobj.h>
+#include <oleidl.h>
+#include <objidl.h>
+#include <ole2.h>
+
 #include "lisp.h"
 #include "w32term.h"
 #include "frame.h"
@@ -359,6 +365,9 @@ #define WS_EX_NOACTIVATE 0x08000000L
 
 static struct w32_display_info *w32_display_info_for_name (Lisp_Object);
 
+static void my_post_msg (W32Msg*, HWND, UINT, WPARAM, LPARAM);
+static unsigned int w32_get_modifiers (void);
+
 /* Let the user specify a display with a frame.
    nil stands for the selected frame--or, if that is not a w32 frame,
    the first display on the list.  */
@@ -2464,6 +2473,174 @@ w32_createhscrollbar (struct frame *f, struct scroll_bar * bar)
   return hwnd;
 }
 
+/* From the DROPFILES struct, extract the filenames and return as a list
+   of strings.  */
+static Lisp_Object
+process_dropfiles (DROPFILES *files)
+{
+  char *start_of_files = (char *) files + files->pFiles;
+  char filename[MAX_UTF8_PATH];
+  Lisp_Object lisp_files = Qnil;
+
+  if (files->fWide)
+    {
+      WCHAR *p = (WCHAR *) start_of_files;
+      for (; *p; p += wcslen (p) + 1)
+	{
+	  filename_from_utf16(p, filename);
+	  lisp_files = Fcons (DECODE_FILE (build_string (filename)),
+			      lisp_files );
+	}
+    }
+  else
+    {
+      char *p = start_of_files;
+      for (; *p; p += strlen(p) + 1)
+	{
+	  filename_from_ansi (p, filename);
+	  lisp_files = Fcons (DECODE_FILE (build_string (filename)),
+			      lisp_files );
+	}
+    }
+  return lisp_files;
+}
+
+Lisp_Object
+w32_process_dnd_data (int format, void *hGlobal)
+{
+  Lisp_Object result = Qnil;
+  HGLOBAL hg = (HGLOBAL) hGlobal;
+
+  switch (format)
+    {
+    case CF_HDROP:
+      {
+	DROPFILES *files = (DROPFILES *) GlobalLock (hg);
+	if (files)
+	  result = process_dropfiles (files);
+	GlobalUnlock (hg);
+	break;
+      }
+    case CF_UNICODETEXT:
+      {
+	WCHAR *text = (WCHAR *) GlobalLock (hg);
+	result = from_unicode_buffer (text);
+	GlobalUnlock (hg);
+	break;
+      }
+    case CF_TEXT:
+      {
+	char *text = (char *) GlobalLock (hg);
+	result = DECODE_SYSTEM (build_unibyte_string (text));
+	GlobalUnlock (hg);
+	break;
+      }
+    }
+
+  GlobalFree (hg);
+
+  return result;
+}
+
+struct w32_drop_target {
+  /* i_drop_target must be the first member.  */
+  IDropTarget i_drop_target;
+  HWND hwnd;
+};
+
+static HRESULT STDMETHODCALLTYPE
+w32_drop_target_QueryInterface (IDropTarget *t, REFIID ri, void **r)
+{
+  return E_NOINTERFACE;
+}
+
+static ULONG STDMETHODCALLTYPE
+w32_drop_target_AddRef (IDropTarget *This)
+{
+  return 1;
+}
+
+static ULONG STDMETHODCALLTYPE
+w32_drop_target_Release (IDropTarget *This)
+{
+  struct w32_drop_target *target = (struct w32_drop_target * ) This;
+  free (target->i_drop_target.lpVtbl);
+  free (target);
+  return 0;
+}
+
+static HRESULT STDMETHODCALLTYPE
+w32_drop_target_DragEnter (IDropTarget *This, IDataObject *pDataObj,
+			   DWORD grfKeyState, POINTL pt, DWORD *pdwEffect)
+{
+  *pdwEffect = DROPEFFECT_COPY;
+  return S_OK;
+}
+
+static HRESULT STDMETHODCALLTYPE
+w32_drop_target_DragOver (IDropTarget *This, DWORD grfKeyState, POINTL pt,
+			  DWORD *pdwEffect)
+{
+  *pdwEffect = DROPEFFECT_COPY;
+  return S_OK;
+}
+
+static HRESULT STDMETHODCALLTYPE
+w32_drop_target_DragLeave (IDropTarget *This)
+{
+  return S_OK;
+}
+
+static HGLOBAL w32_try_get_data (IDataObject *pDataObj, int format)
+{
+  FORMATETC formatetc = { format, NULL, DVASPECT_CONTENT, -1,
+			  TYMED_HGLOBAL };
+  STGMEDIUM stgmedium;
+  HRESULT r = IDataObject_GetData (pDataObj, &formatetc, &stgmedium);
+  if (SUCCEEDED (r))
+    {
+      if (stgmedium.tymed == TYMED_HGLOBAL)
+	return stgmedium.hGlobal;
+      ReleaseStgMedium (&stgmedium);
+    }
+  return NULL;
+}
+
+static HRESULT STDMETHODCALLTYPE
+w32_drop_target_Drop (IDropTarget *This, IDataObject *pDataObj,
+		      DWORD grfKeyState, POINTL pt, DWORD *pdwEffect)
+{
+  struct w32_drop_target *target = (struct w32_drop_target *)This;
+  *pdwEffect = DROPEFFECT_COPY;
+
+  W32Msg msg = {0};
+  msg.dwModifiers = w32_get_modifiers();
+  msg.msg.time = GetMessageTime ();
+  msg.msg.pt.x = pt.x;
+  msg.msg.pt.y = pt.y;
+
+  int format = CF_HDROP;
+  HGLOBAL hGlobal = w32_try_get_data (pDataObj, format);
+
+  if (!hGlobal)
+    {
+      format = CF_UNICODETEXT;
+      hGlobal = w32_try_get_data (pDataObj, format);
+    }
+
+  if (!hGlobal)
+    {
+      format = CF_TEXT;
+      hGlobal = w32_try_get_data (pDataObj, format);
+    }
+
+  if (hGlobal)
+      my_post_msg (&msg, target->hwnd, WM_EMACS_DROP, format,
+		   (LPARAM) hGlobal);
+
+  return S_OK;
+}
+
 static void
 w32_createwindow (struct frame *f, int *coords)
 {
@@ -2548,7 +2725,20 @@ w32_createwindow (struct frame *f, int *coords)
       SetWindowLong (hwnd, WND_BACKGROUND_INDEX, FRAME_BACKGROUND_PIXEL (f));
 
       /* Enable drag-n-drop.  */
-      DragAcceptFiles (hwnd, TRUE);
+      struct w32_drop_target *drop_target =
+	malloc (sizeof (struct w32_drop_target));
+      drop_target->hwnd = hwnd;
+
+      IDropTargetVtbl *vtbl = malloc (sizeof (IDropTargetVtbl));
+      drop_target->i_drop_target.lpVtbl = vtbl;
+      vtbl->QueryInterface = w32_drop_target_QueryInterface;
+      vtbl->AddRef = w32_drop_target_AddRef;
+      vtbl->Release = w32_drop_target_Release;
+      vtbl->DragEnter = w32_drop_target_DragEnter;
+      vtbl->DragOver = w32_drop_target_DragOver;
+      vtbl->DragLeave = w32_drop_target_DragLeave;
+      vtbl->Drop = w32_drop_target_Drop;
+      RegisterDragDrop (hwnd, &drop_target->i_drop_target);
 
       /* Enable system light/dark theme.  */
       w32_applytheme (hwnd);
@@ -3399,6 +3589,7 @@ #define M(msg) { msg, # msg }
       M (WM_EMACS_PAINT),
       M (WM_EMACS_IME_STATUS),
       M (WM_CHAR),
+      M (WM_EMACS_DROP),
 #undef M
       { 0, 0 }
   };
@@ -3465,13 +3656,14 @@ w32_msg_pump (deferred_msg * msg_buf)
 	      /* Produced by complete_deferred_msg; just ignore.  */
 	      break;
 	    case WM_EMACS_CREATEWINDOW:
-	      /* Initialize COM for this window. Even though we don't use it,
-		 some third party shell extensions can cause it to be used in
+	      /* Initialize COM for this window.  Needed for RegisterDragDrop.
+		 Some third party shell extensions can cause it to be used in
 		 system dialogs, which causes a crash if it is not initialized.
 		 This is a known bug in Windows, which was fixed long ago, but
 		 the patch for XP is not publicly available until XP SP3,
 		 and older versions will never be patched.  */
-	      CoInitialize (NULL);
+	      OleInitialize (NULL);
+
 	      w32_createwindow ((struct frame *) msg.wParam,
 				(int *) msg.lParam);
 	      if (!PostThreadMessage (dwMainThreadId, WM_EMACS_DONE, 0, 0))
@@ -5106,7 +5298,6 @@ #define MOUSEEVENTF_FROMTOUCH 0xFF515700
       return 0;
 
     case WM_MOUSEWHEEL:
-    case WM_DROPFILES:
       wmsg.dwModifiers = w32_get_modifiers ();
       my_post_msg (&wmsg, hwnd, msg, wParam, lParam);
       signal_user_input ();
@@ -5597,7 +5788,7 @@ #define WM_TOUCH 576
       }
 
     case WM_EMACS_DESTROYWINDOW:
-      DragAcceptFiles ((HWND) wParam, FALSE);
+      RevokeDragDrop ((HWND) wParam);
       return DestroyWindow ((HWND) wParam);
 
     case WM_EMACS_HIDE_CARET:
diff --git a/src/w32term.c b/src/w32term.c
index 62037e3b2cd..3a627308137 100644
--- a/src/w32term.c
+++ b/src/w32term.c
@@ -3576,81 +3576,6 @@ w32_construct_mouse_wheel (struct input_event *result, W32Msg *msg,
   return Qnil;
 }
 
-static Lisp_Object
-w32_construct_drag_n_drop (struct input_event *result, W32Msg *msg,
-                           struct frame *f)
-{
-  Lisp_Object files;
-  Lisp_Object frame;
-  HDROP hdrop;
-  POINT p;
-  WORD num_files;
-  wchar_t name_w[MAX_PATH];
-#ifdef NTGUI_UNICODE
-  const int use_unicode = 1;
-#else
-  int use_unicode = w32_unicode_filenames;
-  char name_a[MAX_PATH];
-  char file[MAX_UTF8_PATH];
-#endif
-  int i;
-
-  result->kind = DRAG_N_DROP_EVENT;
-  result->code = 0;
-  result->timestamp = msg->msg.time;
-  result->modifiers = msg->dwModifiers;
-
-  hdrop = (HDROP) msg->msg.wParam;
-  DragQueryPoint (hdrop, &p);
-
-#if 0
-  p.x = LOWORD (msg->msg.lParam);
-  p.y = HIWORD (msg->msg.lParam);
-  ScreenToClient (msg->msg.hwnd, &p);
-#endif
-
-  XSETINT (result->x, p.x);
-  XSETINT (result->y, p.y);
-
-  num_files = DragQueryFile (hdrop, 0xFFFFFFFF, NULL, 0);
-  files = Qnil;
-
-  for (i = 0; i < num_files; i++)
-    {
-      if (use_unicode)
-	{
-	  eassert (DragQueryFileW (hdrop, i, NULL, 0) < MAX_PATH);
-	  /* If DragQueryFile returns zero, it failed to fetch a file
-	     name.  */
-	  if (DragQueryFileW (hdrop, i, name_w, MAX_PATH) == 0)
-	    continue;
-#ifdef NTGUI_UNICODE
-	  files = Fcons (from_unicode_buffer (name_w), files);
-#else
-	  filename_from_utf16 (name_w, file);
-	  files = Fcons (DECODE_FILE (build_unibyte_string (file)), files);
-#endif /* NTGUI_UNICODE */
-	}
-#ifndef NTGUI_UNICODE
-      else
-	{
-	  eassert (DragQueryFileA (hdrop, i, NULL, 0) < MAX_PATH);
-	  if (DragQueryFileA (hdrop, i, name_a, MAX_PATH) == 0)
-	    continue;
-	  filename_from_ansi (name_a, file);
-	  files = Fcons (DECODE_FILE (build_unibyte_string (file)), files);
-	}
-#endif
-    }
-
-  DragFinish (hdrop);
-
-  XSETFRAME (frame, f);
-  result->frame_or_window = frame;
-  result->arg = files;
-  return Qnil;
-}
-
 \f
 #if HAVE_W32NOTIFY
 
@@ -5682,11 +5607,26 @@ w32_read_socket (struct terminal *terminal,
 	  }
 	  break;
 
-	case WM_DROPFILES:
-	  f = w32_window_to_frame (dpyinfo, msg.msg.hwnd);
+	case WM_EMACS_DROP:
+	  {
+	    int format = msg.msg.wParam;
+	    Lisp_Object drop_object =
+	      w32_process_dnd_data (format, (void *) msg.msg.lParam);
 
-	  if (f)
-	    w32_construct_drag_n_drop (&inev, &msg, f);
+	    f = w32_window_to_frame (dpyinfo, msg.msg.hwnd);
+	    if (!f || NILP (drop_object))
+	      break;
+
+	    XSETFRAME (inev.frame_or_window, f);
+	    inev.kind = DRAG_N_DROP_EVENT;
+	    inev.code = 0;
+	    inev.timestamp = msg.msg.time;
+	    inev.modifiers = msg.dwModifiers;
+	    ScreenToClient (msg.msg.hwnd, &msg.msg.pt);
+	    XSETINT (inev.x, msg.msg.pt.x);
+	    XSETINT (inev.y, msg.msg.pt.y);
+	    inev.arg = drop_object;
+	  }
 	  break;
 
 	case WM_HSCROLL:
diff --git a/src/w32term.h b/src/w32term.h
index 47be542f570..39e2262e2a8 100644
--- a/src/w32term.h
+++ b/src/w32term.h
@@ -272,6 +272,7 @@ #define CP_DEFAULT 1004
 
 /* w32fns.c */
 extern void w32_default_font_parameter (struct frame* f, Lisp_Object parms);
+extern Lisp_Object w32_process_dnd_data (int format, void *pDataObj);
 
 \f
 #define PIX_TYPE COLORREF
@@ -710,7 +711,8 @@ #define WM_EMACS_BRINGTOTOP            (WM_EMACS_START + 23)
 #define WM_EMACS_INPUT_READY           (WM_EMACS_START + 24)
 #define WM_EMACS_FILENOTIFY            (WM_EMACS_START + 25)
 #define WM_EMACS_IME_STATUS            (WM_EMACS_START + 26)
-#define WM_EMACS_END                   (WM_EMACS_START + 27)
+#define WM_EMACS_DROP                  (WM_EMACS_START + 27)
+#define WM_EMACS_END                   (WM_EMACS_START + 28)
 
 #define WND_FONTWIDTH_INDEX    (0)
 #define WND_LINEHEIGHT_INDEX   (4)
-- 
2.35.1.windows.2