Now that copy mode copies the pane content rather than keeping a

reference to it, it isn't necessary that the pane in copy mode is the
same as the one copying from. Add a -s flag to copy-mode to specify a
different pane for the source content. This means it is possible to view
two places in a pane's history at the same time in different panes, or
copy from a pane's history into an editor or shell in the same pane.

From Anindya Mukherjee.

cfg.c

@@ -284,7 +284,7 @@ cfg_show_causes(struct session *s)
 
 	wme = TAILQ_FIRST(&wp->modes);
 	if (wme == NULL || wme->mode != &window_view_mode)
-		window_pane_set_mode(wp, &window_view_mode, NULL, NULL);
+		window_pane_set_mode(wp, NULL, &window_view_mode, NULL, NULL);
 	for (i = 0; i < cfg_ncauses; i++) {
 		window_copy_add(wp, "%s", cfg_causes[i]);
 		free(cfg_causes[i]);

cmd-choose-tree.c

@@ -86,6 +86,6 @@ cmd_choose_tree_exec(struct cmd *self, struct cmdq_item *item)
 	} else
 		mode = &window_tree_mode;
 
-	window_pane_set_mode(wp, mode, &item->target, args);
+	window_pane_set_mode(wp, NULL, mode, &item->target, args);
 	return (CMD_RETURN_NORMAL);
 }

cmd-copy-mode.c

@@ -30,9 +30,10 @@ const struct cmd_entry cmd_copy_mode_entry = {
 	.name = "copy-mode",
 	.alias = NULL,
 
-	.args = { "eHMt:uq", 0, 0 },
-	.usage = "[-eHMuq] " CMD_TARGET_PANE_USAGE,
+	.args = { "eHMs:t:uq", 0, 0 },
+	.usage = "[-eHMuq] [-s src-pane] " CMD_TARGET_PANE_USAGE,
 
+	.source =  { 's', CMD_FIND_PANE, 0 },
 	.target = { 't', CMD_FIND_PANE, 0 },
 
 	.flags = CMD_AFTERHOOK,
@@ -59,7 +60,7 @@ cmd_copy_mode_exec(struct cmd *self, struct cmdq_item *item)
 	struct cmdq_shared	*shared = item->shared;
 	struct client		*c = item->client;
 	struct session		*s;
-	struct window_pane	*wp = item->target.wp;
+	struct window_pane	*wp = item->target.wp, *swp;
 
 	if (args_has(args, 'q')) {
 		window_pane_reset_mode_all(wp);
@@ -74,11 +75,15 @@ cmd_copy_mode_exec(struct cmd *self, struct cmdq_item *item)
 	}
 
 	if (self->entry == &cmd_clock_mode_entry) {
-		window_pane_set_mode(wp, &window_clock_mode, NULL, NULL);
+		window_pane_set_mode(wp, NULL, &window_clock_mode, NULL, NULL);
 		return (CMD_RETURN_NORMAL);
 	}
 
-	if (!window_pane_set_mode(wp, &window_copy_mode, NULL, args)) {
+	if (args_has(args, 's'))
+		swp = item->source.wp;
+	else
+		swp = wp;
+	if (!window_pane_set_mode(wp, swp, &window_copy_mode, NULL, args)) {
 		if (args_has(args, 'M'))
 			window_copy_start_drag(c, &shared->mouse);
 	}

cmd-find-window.c

@@ -116,7 +116,8 @@ cmd_find_window_exec(struct cmd *self, struct cmdq_item *item)
 		args_set(new_args, 'Z', NULL);
 	args_set(new_args, 'f', filter);
 
-	window_pane_set_mode(wp, &window_tree_mode, &item->target, new_args);
+	window_pane_set_mode(wp, NULL, &window_tree_mode, &item->target,
+	    new_args);
 
 	args_free(new_args);
 	free(filter);

cmd-queue.c

@@ -511,8 +511,10 @@ cmdq_print(struct cmdq_item *item, const char *fmt, ...)
 	} else {
 		wp = c->session->curw->window->active;
 		wme = TAILQ_FIRST(&wp->modes);
-		if (wme == NULL || wme->mode != &window_view_mode)
-			window_pane_set_mode(wp, &window_view_mode, NULL, NULL);
+		if (wme == NULL || wme->mode != &window_view_mode) {
+			window_pane_set_mode(wp, NULL, &window_view_mode, NULL,
+			    NULL);
+		}
 		window_copy_add(wp, "%s", msg);
 	}
 

cmd-run-shell.c

@@ -82,7 +82,7 @@ cmd_run_shell_print(struct job *job, const char *msg)
 
 	wme = TAILQ_FIRST(&wp->modes);
 	if (wme == NULL || wme->mode != &window_view_mode)
-		window_pane_set_mode(wp, &window_view_mode, NULL, NULL);
+		window_pane_set_mode(wp, NULL, &window_view_mode, NULL, NULL);
 	window_copy_add(wp, "%s", msg);
 }
 

tmux.1

@@ -1608,6 +1608,7 @@ command is:
 .Bl -tag -width Ds
 .It Xo Ic copy-mode
 .Op Fl eHMqu
+.Op Fl s Ar src-pane
 .Op Fl t Ar target-pane
 .Xc
 Enter copy mode.
@@ -1621,6 +1622,11 @@ begins a mouse drag (only valid if bound to a mouse key binding, see
 hides the position indicator in the top right.
 .Fl q
 cancels copy mode and any other modes.
+.Fl s
+copies from
+.Ar src-pane
+instead of
+.Ar target-pane.
 .Pp
 .Fl e
 specifies that scrolling to the bottom of the history (to the visible screen)

tmux.h

@@ -848,6 +848,7 @@ struct window_mode {
 /* Active window mode. */
 struct window_mode_entry {
 	struct window_pane		*wp;
+	struct window_pane		*swp;
 
 	const struct window_mode	*mode;
 	void				*data;
@@ -2537,8 +2538,8 @@ void		 window_pane_unset_palette(struct window_pane *, u_int);
 void		 window_pane_reset_palette(struct window_pane *);
 int		 window_pane_get_palette(struct window_pane *, int);
 int		 window_pane_set_mode(struct window_pane *,
-		     const struct window_mode *, struct cmd_find_state *,
-		     struct args *);
+		     struct window_pane *, const struct window_mode *,
+		     struct cmd_find_state *, struct args *);
 void		 window_pane_reset_mode(struct window_pane *);
 void		 window_pane_reset_mode_all(struct window_pane *);
 int		 window_pane_key(struct window_pane *, struct client *,

window-copy.c

@@ -130,7 +130,7 @@ static void	window_copy_rectangle_toggle(struct window_mode_entry *);
 static void	window_copy_move_mouse(struct mouse_event *);
 static void	window_copy_drag_update(struct client *, struct mouse_event *);
 static void	window_copy_drag_release(struct client *, struct mouse_event *);
-static struct screen* window_copy_clone_screen(struct screen *src);
+static struct screen* window_copy_clone_screen(struct screen *, struct screen*);
 
 const struct window_mode window_copy_mode = {
 	.name = "copy-mode",
@@ -299,21 +299,29 @@ window_copy_scroll_timer(__unused int fd, __unused short events, void *arg)
 }
 
 static struct screen *
-window_copy_clone_screen(struct screen *src)
+window_copy_clone_screen(struct screen *src, struct screen *hint)
 {
 	struct screen			*dst;
 	struct screen_write_ctx		 ctx;
+	u_int				 dy, sy;
 
 	dst = xcalloc(1, sizeof *dst);
-	screen_init(dst, screen_size_x(src),
-	    screen_hsize(src) + screen_size_y(src), src->grid->hlimit);
-	grid_duplicate_lines(dst->grid, 0, src->grid, 0,
-	    screen_hsize(src) + screen_size_y(src));
-	dst->grid->sy = screen_size_y(src);
-	dst->grid->hsize = screen_hsize(src);
+
+	sy = screen_hsize(src) + screen_size_y(src);
+	if (screen_size_y(hint) > sy)
+		dy = screen_size_y(hint);
+	else
+		dy = sy;
+	screen_init(dst, screen_size_x(src), dy, src->grid->hlimit);
+
+	grid_duplicate_lines(dst->grid, 0, src->grid, 0, sy);
+	if (screen_size_y(hint) < sy) {
+		dst->grid->sy = screen_size_y(hint);
+		dst->grid->hsize = sy - screen_size_y(hint);
+	}
 
 	screen_write_start(&ctx, NULL, dst);
-	screen_write_cursormove(&ctx, src->cx, src->cy, 0);
+	screen_write_cursormove(&ctx, 0, dst->grid->sy - 1, 0);
 	screen_write_stop(&ctx);
 
 	return (dst);
@@ -361,14 +369,14 @@ static struct screen *
 window_copy_init(struct window_mode_entry *wme,
     __unused struct cmd_find_state *fs, struct args *args)
 {
-	struct window_pane		*wp = wme->wp;
+	struct window_pane		*wp = wme->swp;
 	struct window_copy_mode_data	*data;
 	struct screen_write_ctx		 ctx;
 	u_int				 i;
 
 	data = window_copy_common_init(wme);
 
-	data->backing = window_copy_clone_screen(&wp->base);
+	data->backing = window_copy_clone_screen(&wp->base, &data->screen);
 	data->cx = data->backing->cx;
 	data->cy = data->backing->cy;
 
@@ -2001,7 +2009,7 @@ static enum window_copy_cmd_action
 window_copy_cmd_refresh_from_pane(struct window_copy_cmd_state *cs)
 {
 	struct window_mode_entry	*wme = cs->wme;
-	struct window_pane		*wp = wme->wp;
+	struct window_pane		*wp = wme->swp;
 	struct window_copy_mode_data	*data = wme->data;
 
 	if (data->viewmode)
@@ -2009,7 +2017,7 @@ window_copy_cmd_refresh_from_pane(struct window_copy_cmd_state *cs)
 
 	screen_free(data->backing);
 	free(data->backing);
-	data->backing = window_copy_clone_screen(&wp->base);
+	data->backing = window_copy_clone_screen(&wp->base, &data->screen);
 
 	return (WINDOW_COPY_CMD_REDRAW);
 }
@@ -2964,6 +2972,7 @@ window_copy_write_line(struct window_mode_entry *wme,
 	struct grid_cell		 gc;
 	char				 hdr[512];
 	size_t				 size = 0;
+	u_int				 hsize = screen_hsize(data->backing);
 
 	style_apply(&gc, oo, "mode-style");
 	gc.flags |= GRID_FLAG_NOPALETTE;
@@ -2972,23 +2981,20 @@ window_copy_write_line(struct window_mode_entry *wme,
 		if (data->searchmark == NULL) {
 			if (data->timeout) {
 				size = xsnprintf(hdr, sizeof hdr,
-			    		"(timed out) [%u/%u]", data->oy,
-					screen_hsize(data->backing));
+				    "(timed out) [%u/%u]", data->oy, hsize);
 			} else {
 				size = xsnprintf(hdr, sizeof hdr,
-					"[%u/%u]", data->oy,
-					screen_hsize(data->backing));
+				    "[%u/%u]", data->oy, hsize);
 			}
 		} else {
 			if (data->searchthis == -1) {
 				size = xsnprintf(hdr, sizeof hdr,
 				    "(%u results) [%d/%u]", data->searchcount,
-				    data->oy, screen_hsize(data->backing));
+				    data->oy, hsize);
 			} else {
 				size = xsnprintf(hdr, sizeof hdr,
 				    "(%u/%u results) [%d/%u]", data->searchthis,
-				    data->searchcount, data->oy,
-				    screen_hsize(data->backing));
+				    data->searchcount, data->oy, hsize);
 			}
 		}
 		if (size > screen_size_x(s))
@@ -3000,8 +3006,7 @@ window_copy_write_line(struct window_mode_entry *wme,
 
 	if (size < screen_size_x(s)) {
 		screen_write_cursormove(ctx, 0, py, 0);
-		screen_write_copy(ctx, data->backing, 0,
-		    (screen_hsize(data->backing) - data->oy) + py,
+		screen_write_copy(ctx, data->backing, 0, hsize - data->oy + py,
 		    screen_size_x(s) - size, 1, data->searchmark, &gc);
 	}
 

window.c

@@ -1067,8 +1067,9 @@ window_pane_get_palette(struct window_pane *wp, int c)
 }
 
 int
-window_pane_set_mode(struct window_pane *wp, const struct window_mode *mode,
-    struct cmd_find_state *fs, struct args *args)
+window_pane_set_mode(struct window_pane *wp, struct window_pane *swp,
+    const struct window_mode *mode, struct cmd_find_state *fs,
+    struct args *args)
 {
 	struct window_mode_entry	*wme;
 
@@ -1085,6 +1086,7 @@ window_pane_set_mode(struct window_pane *wp, const struct window_mode *mode,
 	} else {
 		wme = xcalloc(1, sizeof *wme);
 		wme->wp = wp;
+		wme->swp = swp;
 		wme->mode = mode;
 		wme->prefix = 1;
 		TAILQ_INSERT_HEAD(&wp->modes, wme, entry);