patch 8.1.1525: cannot move a popup window with the mouse

Problem:    Cannot move a popup window with the mouse.
Solution:   Add the "drag" property and make it possible to drag a popup
            window by its border.

runtime/doc/popup.txt

@@ -95,7 +95,7 @@ IMPLEMENTATION:
 - For the "moved" property also include mouse movement?
 - When selecting text in the popup with modeless selection, do not select
   outside of the popup and don't select the border or padding.
-- Allow the user to drag the popup window when the "dragging" property is set.
+- Add test for dragging the popup window.
 - Make redrawing more efficient and avoid flicker:
     - put popup menu also put in popup_mask?
 - Invoke filter with character before mapping?
@@ -277,7 +277,7 @@ popup_menu({text}, {options})				 *popup_menu()*
 
 
 popup_move({id}, {options})					*popup_move()*
-		Move popup {id} to the position speficied with {options}.
+		Move popup {id} to the position specified with {options}.
 		{options} may contain the items from |popup_create()| that
 		specify the popup position: "line", "col", "pos", "maxheight",
 		"minheight", "maxwidth" and "minwidth".
@@ -293,6 +293,7 @@ popup_notification({text}, {options})			 *popup_notification()*
 				\ 'time': 3000,
 				\ 'tab': -1,
 				\ 'zindex': 200,
+				\ 'drag': 1,
 				\ 'highlight': 'WarningMsg',
 				\ 'border': [],
 				\ 'padding': [0,1,0,1],
@@ -409,9 +410,13 @@ The second argument of |popup_create()| is a dictionary with options:
 			{only -1 and 0 are implemented}
 	title		Text to be displayed above the first item in the
 			popup, on top of any border.  If there is no top
-			border on line of padding is added to put the title on.
+			border one line of padding is added to put the title
+			on.
 			{not implemented yet}
 	wrap		TRUE to make the lines wrap (default TRUE).
+	drag		TRUE to allow the popup to be dragged with the mouse
+			by grabbing at at the border.  Has no effect if the
+			popup does not have a border.
 	highlight	Highlight group name to use for the text, stored in
 			the 'wincolor' option.
 	padding		List with numbers, defining the padding
@@ -442,7 +447,7 @@ The second argument of |popup_create()| is a dictionary with options:
 			By default a double line is used all around when
 			'encoding' is "utf-8", otherwise ASCII characters are
 			used.
-	zindex		Priority for the popup, default 50.  Mininum value is
+	zindex		Priority for the popup, default 50.  Minimum value is
 			1, maximum value is 32000.
 	time		Time in milliseconds after which the popup will close.
 			When omitted |popup_close()| must be used.

src/popupwin.c

@@ -164,6 +164,68 @@ set_moved_columns(win_T *wp, int flags)
     }
 }
 
+/*
+ * Return TRUE if "row"/"col" is on the border of the popup.
+ * The values are relative to the top-left corner.
+ */
+    int
+popup_on_border(win_T *wp, int row, int col)
+{
+    return (row == 0 && wp->w_popup_border[0] > 0)
+	    || (row == popup_height(wp) - 1 && wp->w_popup_border[2] > 0)
+	    || (col == 0 && wp->w_popup_border[3] > 0)
+	    || (col == popup_width(wp) - 1 && wp->w_popup_border[1] > 0);
+}
+
+// Values set when dragging a popup window starts.
+static int drag_start_row;
+static int drag_start_col;
+static int drag_start_wantline;
+static int drag_start_wantcol;
+
+/*
+ * Mouse down on border of popup window: start dragging it.
+ * Uses mouse_col and mouse_row.
+ */
+    void
+popup_start_drag(win_T *wp)
+{
+    drag_start_row = mouse_row;
+    drag_start_col = mouse_col;
+    // TODO: handle using different corner
+    if (wp->w_wantline == 0)
+	drag_start_wantline = wp->w_winrow + 1;
+    else
+	drag_start_wantline = wp->w_wantline;
+    if (wp->w_wantcol == 0)
+	drag_start_wantcol = wp->w_wincol + 1;
+    else
+	drag_start_wantcol = wp->w_wantcol;
+}
+
+/*
+ * Mouse moved while dragging a popup window: adjust the window popup position.
+ */
+    void
+popup_drag(win_T *wp)
+{
+    // The popup may be closed before dragging stops.
+    if (!win_valid_popup(wp))
+	return;
+
+    wp->w_wantline = drag_start_wantline + (mouse_row - drag_start_row);
+    if (wp->w_wantline < 1)
+	wp->w_wantline = 1;
+    if (wp->w_wantline > Rows)
+	wp->w_wantline = Rows;
+    wp->w_wantcol = drag_start_wantcol + (mouse_col - drag_start_col);
+    if (wp->w_wantcol < 1)
+	wp->w_wantcol = 1;
+    if (wp->w_wantcol > Columns)
+	wp->w_wantcol = Columns;
+
+    popup_adjust_position(wp);
+}
 
 #if defined(FEAT_TIMERS)
     static void
@@ -237,6 +299,8 @@ apply_options(win_T *wp, buf_T *buf UNUSED, dict_T *dict)
 	wp->w_p_wrap = nr != 0;
     }
 
+    wp->w_popup_drag = dict_get_number(dict, (char_u *)"drag");
+
     di = dict_find(dict, (char_u *)"callback", -1);
     if (di != NULL)
     {
@@ -798,6 +862,7 @@ popup_create(typval_T *argvars, typval_T *rettv, create_type_T type)
 	wp->w_popup_padding[3] = 1;
 	set_string_option_direct_in_win(wp, (char_u *)"wincolor", -1,
 				(char_u *)"WarningMsg", OPT_FREE|OPT_LOCAL, 0);
+	wp->w_popup_drag = 1;
     }
 
     // Deal with options.

src/proto/popupwin.pro

@@ -1,4 +1,7 @@
 /* popupwin.c */
+int popup_on_border(win_T *wp, int row, int col);
+void popup_start_drag(win_T *wp);
+void popup_drag(win_T *wp);
 int popup_height(win_T *wp);
 int popup_width(win_T *wp);
 void popup_adjust_position(win_T *wp);

src/proto/window.pro

@@ -3,6 +3,7 @@ void do_window(int nchar, long Prenum, int xchar);
 void get_wincmd_addr_type(char_u *arg, exarg_T *eap);
 int win_split(int size, int flags);
 int win_split_ins(int size, int flags, win_T *new_wp, int dir);
+int win_valid_popup(win_T *win);
 int win_valid(win_T *win);
 int win_valid_any_tab(win_T *win);
 int win_count(void);

src/structs.h

@@ -2909,6 +2909,7 @@ struct window_S
     linenr_T	w_popup_lnum;	    // close popup if cursor not on this line
     colnr_T	w_popup_mincol;	    // close popup if cursor before this col
     colnr_T	w_popup_maxcol;	    // close popup if cursor after this col
+    int		w_popup_drag;	    // allow moving the popup with the mouse
 
 # if defined(FEAT_TIMERS)
     timer_T	*w_popup_timer;	    // timer for closing popup window

src/ui.c

@@ -1002,7 +1002,7 @@ static void clip_update_modeless_selection(VimClipboard *, int, int,
 
 /*
  * Start, continue or end a modeless selection.  Used when editing the
- * command-line and in the cmdline window.
+ * command-line, in the cmdline window and when the mouse is in a popup window.
  */
     void
 clip_modeless(int button, int is_click, int is_drag)
@@ -2842,6 +2842,7 @@ jump_to_mouse(
 #endif
 #ifdef FEAT_TEXT_PROP
     static int   in_popup_win = FALSE;
+    static win_T *popup_dragwin = NULL;
 #endif
     static int	prev_row = -1;
     static int	prev_col = -1;
@@ -2869,6 +2870,9 @@ jump_to_mouse(
 	    flags &= ~(MOUSE_FOCUS | MOUSE_DID_MOVE);
 	dragwin = NULL;
 	did_drag = FALSE;
+#ifdef FEAT_TEXT_PROP
+	popup_dragwin = NULL;
+#endif
     }
 
     if ((flags & MOUSE_DID_MOVE)
@@ -2910,7 +2914,15 @@ retnomove:
 #ifdef FEAT_TEXT_PROP
 	// Continue a modeless selection in a popup window.
 	if (in_popup_win)
+	{
+	    if (popup_dragwin != NULL)
+	    {
+		// dragging a popup window
+		popup_drag(popup_dragwin);
+		return IN_UNKNOWN;
+	    }
 	    return IN_OTHER_WIN;
+	}
 #endif
 	return IN_BUFFER;
     }
@@ -2936,22 +2948,28 @@ retnomove:
 
     if (!(flags & MOUSE_FOCUS))
     {
-	if (row < 0 || col < 0)			/* check if it makes sense */
+	if (row < 0 || col < 0)			// check if it makes sense
 	    return IN_UNKNOWN;
 
-	/* find the window where the row is in */
+	// find the window where the row is in
 	wp = mouse_find_win(&row, &col, FIND_POPUP);
 	if (wp == NULL)
 	    return IN_UNKNOWN;
 	dragwin = NULL;
 
 #ifdef FEAT_TEXT_PROP
-	// Click in a popup window may start modeless selection, but not much
+	// Click in a popup window may start dragging or modeless selection,
-	// else.
+	// but not much else.
 	if (bt_popup(wp->w_buffer))
 	{
 	    on_sep_line = 0;
 	    in_popup_win = TRUE;
+	    if (wp->w_popup_drag && popup_on_border(wp, row, col))
+	    {
+		popup_dragwin = wp;
+		popup_start_drag(wp);
+		return IN_UNKNOWN;
+	    }
 # ifdef FEAT_CLIPBOARD
 	    return IN_OTHER_WIN;
 # else
@@ -2959,6 +2977,7 @@ retnomove:
 # endif
 	}
 	in_popup_win = FALSE;
+	popup_dragwin = NULL;
 #endif
 #ifdef FEAT_MENU
 	if (row == -1)
@@ -3127,9 +3146,17 @@ retnomove:
 	    return IN_OTHER_WIN;
 #endif
 #ifdef FEAT_TEXT_PROP
-	// Continue a modeless selection in a popup window.
 	if (in_popup_win)
+	{
+	    if (popup_dragwin != NULL)
+	    {
+		// dragging a popup window
+		popup_drag(popup_dragwin);
+		return IN_UNKNOWN;
+	    }
+	    // continue a modeless selection in a popup window
 	    return IN_OTHER_WIN;
+	}
 #endif
 
 	row -= W_WINROW(curwin);

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1525,
 /**/
     1524,
 /**/

src/window.c

@@ -1371,7 +1371,7 @@ win_init_some(win_T *newp, win_T *oldp)
 /*
  * Return TRUE if "win" is a global popup or a popup in the current tab page.
  */
-    static int
+    int
 win_valid_popup(win_T *win UNUSED)
 {
 #ifdef FEAT_TEXT_PROP