Improve accessibility of window dividers. (Bug#20183)

* lisp/faces.el (window-divider)
(window-divider-first-pixel, window-divider-last-pixel): Change
membership from `frames' to `window-divider' customization group.
* lisp/frame.el (window-divider): New customization group.
(window-divider-mode): New minor mode.
(window-divider-default-bottom-width)
(window-divider-default-right-width): New options.
(frame--window-divider-previous-mode): New variable.
(frame-window-divider-width-valid-p)
(frame--window-divider-mode-apply)
(frame--window-divider-mode-set-and-apply): New functions.
* lisp/menu-bar.el (menu-bar-options-save): Save
window-divider-mode settings.
(menu-bar-window-divider-customize)
(menu-bar-bottom-and-right-window-divider)
(menu-bar-right-window-divider, menu-bar-bottom-window-divider)
(menu-bar-no-window-divider): New functions.
(menu-bar-showhide-window-divider-menu): New variable.
(menu-bar-showhide-menu): Show/hide window divider menu.
* lisp/mouse.el (mouse-split-window-vertically)
(mouse-split-window-horizontally): Replace `error' by
`user-error'.  Bind `window-combination-resize' to nil.
(top-level): Add/reorder mouse key bindings on mode- and
vertical-line.

1 files changed, 91 insertions, 1 deletions

diff --git a/lisp/menu-bar.el b/lisp/menu-bar.el
index 22a0b8faaba..5a69084f98d 100644
--- a/lisp/menu-bar.el
+++ b/lisp/menu-bar.el
@@ -683,7 +683,7 @@ by \"Save Options\" in Custom buffers.")
     (dolist (elt '(scroll-bar-mode
 		   debug-on-quit debug-on-error
 		   ;; Somehow this works, when tool-bar and menu-bar don't.
-		   tooltip-mode
+		   tooltip-mode window-divider-mode
 		   save-place uniquify-buffer-name-style fringe-mode
 		   indicate-empty-lines indicate-buffer-boundaries
 		   case-fold-search font-use-system-font
@@ -711,6 +711,92 @@ by \"Save Options\" in Custom buffers.")
 
 ;; The "Show/Hide" submenu of menu "Options"
 
+(defun menu-bar-window-divider-customize ()
+  "Show customization buffer for `window-divider' group."
+  (interactive)
+  (customize-group 'window-divider))
+
+(defun menu-bar-bottom-and-right-window-divider ()
+  "Display dividers on the bottom and right of each window."
+  (interactive)
+  (customize-set-variable 'window-divider-mode t))
+
+(defun menu-bar-right-window-divider ()
+  "Display dividers only on the right of each window."
+  (interactive)
+  (customize-set-variable 'window-divider-mode 'right-only))
+
+(defun menu-bar-bottom-window-divider ()
+  "Display dividers only at the bottom of each window."
+  (interactive)
+  (customize-set-variable 'window-divider-mode 'bottom-only))
+
+(defun menu-bar-no-window-divider ()
+  "Do not display window dividers."
+  (interactive)
+  (customize-set-variable 'window-divider-mode nil))
+
+;; For the radio buttons below we check whether the respective dividers
+;; are displayed on the selected frame.  This is not fully congruent
+;; with `window-divder-mode' but makes the menu entries work also when
+;; dividers are displayed by manipulating frame parameters directly.
+(defvar menu-bar-showhide-window-divider-menu
+  (let ((menu (make-sparse-keymap "Window Divider")))
+    (bindings--define-key menu [customize]
+      '(menu-item "Customize" menu-bar-window-divider-customize
+                  :help "Customize window dividers"
+                  :visible (memq (window-system) '(x w32))))
+
+    (bindings--define-key menu [bottom-and-right]
+      '(menu-item "Bottom and Right"
+                  menu-bar-bottom-and-right-window-divider
+                  :help "Display window divider on the bottom and right of each window"
+                  :visible (memq (window-system) '(x w32))
+                  :button (:radio
+			   . (and (frame-window-divider-width-valid-p
+				   (cdr (assq 'bottom-divider-width
+					      (frame-parameters))))
+				  (frame-window-divider-width-valid-p
+				   (cdr (assq 'right-divider-width
+					      (frame-parameters))))))))
+    (bindings--define-key menu [right-only]
+      '(menu-item "Right Only"
+                  menu-bar-right-window-divider
+                  :help "Display window divider on the right of each window only"
+                  :visible (memq (window-system) '(x w32))
+                  :button (:radio
+			   . (and (not (frame-window-divider-width-valid-p
+					(cdr (assq 'bottom-divider-width
+						   (frame-parameters)))))
+				  (frame-window-divider-width-valid-p
+				   (cdr (assq 'right-divider-width
+						     (frame-parameters))))))))
+    (bindings--define-key menu [bottom-only]
+      '(menu-item "Bottom Only"
+                  menu-bar-bottom-window-divider
+                  :help "Display window divider on the bottom of each window only"
+                  :visible (memq (window-system) '(x w32))
+                  :button (:radio
+			   . (and (frame-window-divider-width-valid-p
+				   (cdr (assq 'bottom-divider-width
+					      (frame-parameters))))
+				  (not (frame-window-divider-width-valid-p
+					(cdr (assq 'right-divider-width
+						   (frame-parameters)))))))))
+    (bindings--define-key menu [no-divider]
+      '(menu-item "None"
+                  menu-bar-no-window-divider
+                  :help "Do not display window dividers"
+                  :visible (memq (window-system) '(x w32))
+                  :button (:radio
+			   . (and (not (frame-window-divider-width-valid-p
+					(cdr (assq 'bottom-divider-width
+						   (frame-parameters)))))
+				  (not (frame-window-divider-width-valid-p
+					(cdr (assq 'right-divider-width
+						   (frame-parameters)))))))))
+    menu))
+
 (defun menu-bar-showhide-fringe-ind-customize ()
   "Show customization buffer for `indicate-buffer-boundaries'."
   (interactive)
@@ -1072,6 +1158,10 @@ mail status in mode line"))
                                   (frame-visible-p
                                    (symbol-value 'speedbar-frame))))))
 
+    (bindings--define-key menu [showhide-window-divider]
+      `(menu-item "Window Divider" ,menu-bar-showhide-window-divider-menu
+                  :visible (memq (window-system) '(x w32))))
+
     (bindings--define-key menu [showhide-fringe]
       `(menu-item "Fringe" ,menu-bar-showhide-fringe-menu
                   :visible (display-graphic-p)))