master 1694f82e5f: Add user options to move point and scroll window during DND

[Po Lu]

branch: master
commit 1694f82e5f91f1ea96604c7c0aee4537fbada765
Author: Po Lu <luangruo@yahoo.com>
Commit: Po Lu <luangruo@yahoo.com>

    Add user options to move point and scroll window during DND
    
    * doc/emacs/frames.texi (Drag and Drop):
    * etc/NEWS: Document new options 'dnd-scroll-margin' and
    'dnd-indicate-insertion-point'.
    * lisp/dnd.el (dnd-protocol-alist):
    (dnd-open-remote-file-function):
    (dnd-open-file-other-window): Add right group to defcustoms.
    (dnd-scroll-margin, dnd-indicate-insertion-point): New user
    options.
    (dnd-handle-movement): New function.
    * lisp/x-dnd.el (x-dnd-handle-xdnd):
    (x-dnd-handle-motif): Call `dnd-handle-movement' when
    appropriate.
---
 doc/emacs/frames.texi | 12 ++++++++++
 etc/NEWS              |  5 +++++
 lisp/dnd.el           | 61 ++++++++++++++++++++++++++++++++++++++++++++++-----
 lisp/x-dnd.el         |  5 +++--
 4 files changed, 75 insertions(+), 8 deletions(-)

diff --git a/doc/emacs/frames.texi b/doc/emacs/frames.texi
index 7489344cda..560870a4ed 100644
--- a/doc/emacs/frames.texi
+++ b/doc/emacs/frames.texi
@@ -1196,6 +1196,18 @@ the variable @code{dnd-open-file-other-window}.
   The XDND and Motif drag and drop protocols, and the old KDE 1.x
 protocol, are currently supported.
 
+@vindex dnd-indicate-insertion-point
+@vindex dnd-scroll-margin
+
+  It can be difficult to scroll a window or determine where dropped
+text will be inserted while dragging text onto an Emacs window.
+Setting the option @var{dnd-indicate-insertion-point} to a
+non-@code{nil} value makes point move to the location any dropped text
+will be inserted when the mouse moves in a window during drag, and
+setting @code{dnd-scroll-margin} to an integer value causes a window
+to be scrolled if the mouse moves within that many lines of the top
+or bottom of the window during drag.
+
 @vindex mouse-drag-and-drop-region
   Emacs can also optionally drag the region with the mouse into
 another portion of this or another buffer.  To enable that, customize
diff --git a/etc/NEWS b/etc/NEWS
index 199f07a033..037a9724d8 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -195,6 +195,11 @@ to another program.
 If non-nil, this option allows scrolling a window while dragging text
 around without a scroll wheel.
 
++++
+** New user options 'dnd-indicate-insertion-point' and 'dnd-scroll-margin'.
+These options allow adjusting point and scrolling a window when
+dragging items from another program.
+
 +++
 ** New function 'command-query'.
 This function makes its argument command prompt the user for
diff --git a/lisp/dnd.el b/lisp/dnd.el
index 97e81e9bf1..8b11973eb4 100644
--- a/lisp/dnd.el
+++ b/lisp/dnd.el
@@ -42,8 +42,7 @@
   `((,(purecopy "^file:///")  . dnd-open-local-file)   ; XDND format.
     (,(purecopy "^file://")   . dnd-open-file)         ; URL with host
     (,(purecopy "^file:")     . dnd-open-local-file)   ; Old KDE, Motif, Sun
-    (,(purecopy "^\\(https?\\|ftp\\|file\\|nfs\\)://") . dnd-open-file)
-   )
+    (,(purecopy "^\\(https?\\|ftp\\|file\\|nfs\\)://") . dnd-open-file))
 
   "The functions to call for different protocols when a drop is made.
 This variable is used by `dnd-handle-one-url' and `dnd-handle-file-name'.
@@ -57,7 +56,8 @@ If no match is found, the URL is inserted as text by calling 
`dnd-insert-text'.
 The function shall return the action done (move, copy, link or private)
 if some action was made, or nil if the URL is ignored."
   :version "22.1"
-  :type '(repeat (cons (regexp) (function))))
+  :type '(repeat (cons (regexp) (function)))
+  :group 'dnd)
 
 
 (defcustom dnd-open-remote-file-function
@@ -73,17 +73,66 @@ Predefined functions are `dnd-open-local-file' and 
`dnd-open-remote-url'.
 is the default on MS-Windows.  `dnd-open-remote-url' uses `url-handler-mode'
 and is the default except for MS-Windows."
   :version "22.1"
-  :type 'function)
+  :type 'function
+  :group 'dnd)
 
 
 (defcustom dnd-open-file-other-window nil
   "If non-nil, always use `find-file-other-window' to open dropped files."
   :version "22.1"
-  :type 'boolean)
-
+  :type 'boolean
+  :group 'dnd)
+
+(defcustom dnd-scroll-margin nil
+  "The scroll margin inside a window underneath the cursor during 
drag-and-drop.
+If the mouse moves this many lines close to the top or bottom of
+a window while dragging text, then that window will be scrolled
+down and up respectively."
+  :type '(choice (const :tag "Don't scroll during mouse movement")
+                 (integer :tag "This many lines from window top or bottom"))
+  :version "29.1"
+  :group 'dnd)
+
+(defcustom dnd-indicate-insertion-point nil
+  "Whether or not point should follow the position of the mouse.
+If non-nil, the point of the window underneath the mouse will be
+adjusted to reflect where any text will be inserted upon drop
+when the mouse moves while receiving a drop from another
+program."
+  :type 'boolean
+  :version "29.1"
+  :group 'dnd)
 
 ;; Functions
 
+(defun dnd-handle-movement (posn)
+  "Handle mouse movement to POSN when receiving a drop from another program."
+  (when dnd-scroll-margin
+    (ignore-errors
+      (let* ((row (cdr (posn-col-row posn)))
+             (window (when (windowp (posn-window posn))
+                       (posn-window posn)))
+             (text-height (window-text-height window))
+             ;; Make sure it's possible to scroll both up
+             ;; and down if the margin is too large for the
+             ;; window.
+             (margin (min (/ text-height 3) dnd-scroll-margin)))
+        ;; At 2 lines, the window becomes too small for any
+        ;; meaningful scrolling.
+        (unless (<= text-height 2)
+          (cond
+           ;; Inside the bottom scroll margin, scroll up.
+           ((> row (- text-height margin))
+            (with-selected-window window
+              (scroll-up 1)))
+           ;; Inside the top scroll margin, scroll down.
+           ((< row margin)
+            (with-selected-window window
+              (scroll-down 1))))))))
+  (when dnd-indicate-insertion-point
+    (ignore-errors
+      (goto-char (posn-point posn)))))
+
 (defun dnd-handle-one-url (window action url)
   "Handle one dropped url by calling the appropriate handler.
 The handler is first located by looking at `dnd-protocol-alist'.
diff --git a/lisp/x-dnd.el b/lisp/x-dnd.el
index e26703ad84..af9c7b83d9 100644
--- a/lisp/x-dnd.el
+++ b/lisp/x-dnd.el
@@ -499,7 +499,7 @@ FORMAT is 32 (not used).  MESSAGE is the data part of an 
XClientMessageEvent."
                       )))
           (x-send-client-message
            frame dnd-source frame "XdndStatus" 32 list-to-send)
-          ))
+           (dnd-handle-movement (event-start event))))
 
        ((equal "XdndLeave" message)
         (x-dnd-forget-drop window))
@@ -676,7 +676,8 @@ FORMAT is 32 (not used).  MESSAGE is the data part of an 
XClientMessageEvent."
                                      frame
                                      "_MOTIF_DRAG_AND_DROP_MESSAGE"
                                      8
-                                     reply)))
+                                     reply)
+               (dnd-handle-movement (event-start event))))
 
            ((eq message-type 'XmOPERATION_CHANGED)
             (let* ((state (x-dnd-get-state-for-frame frame))