recenter-top-bottom (emacs-mode) (#1767)

* recenter-top-bottom

Emacs default behavior of (C-l recenter-top-bottom)

* fix: window-recenter-top-bottom should return smt

* return prev keymap

* removed unused variable

src/commands/window.lisp

@@ -124,6 +124,13 @@
   (redraw-display)
   t)
 
+(define-command recenter-top-bottom (p) (:universal-nil)
+  "Scroll so that the cursor is in the middle/top/bottom."
+  (clear-screens-of-window-list)
+  (unless p (window-recenter-top-bottom (current-window)))
+  (redraw-display)
+  t)
+
 (define-command split-active-window-vertically (&optional n) (:universal-nil)
   "Split the current window vertically."
   (split-window-vertically (current-window) :height n)

src/internal-packages.lisp

@@ -353,6 +353,7 @@
   ;; virtual-line
   (:export
    :window-recenter
+   :window-recenter-top-bottom
    :window-cursor-x
    :window-cursor-y
    :backward-line-wrap

src/window/virtual-line.lisp

@@ -21,6 +21,20 @@ If FROM-BOTTOM is T, start counting from the bottom."
       (window-scroll window n)
       n)))
 
+(defun window-recenter-top-bottom (window)
+  "In first call recenter WINDOW to the middle line.
+If cursor is already in the middle of WINDOW then move cursor in the top position.
+If cursor is on top then move move WINDOW to the bottom."
+  (let* ((line (window-cursor-y window))
+         (window-height (window-height-without-modeline window))
+         (middle (floor window-height 2))
+         (scrolloff (min (floor (/ (window-height window) 2)) 0))
+         (top 0))
+    (cond
+      ((= line middle) (window-recenter window :line scrolloff :from-bottom nil))
+      ((= line top) (window-recenter window :line scrolloff :from-bottom t))
+      (t (window-recenter window :line nil :from-bottom nil)))))
+
 (defun %calc-window-cursor-x (point window)
   "Return (values cur-x next). the 'next' is a flag if the cursor goes to
 next line because it is at the end of width."