initial commit

with odd header line behavior

center-content.el

@@ -0,0 +1,100 @@
+;;; center-content.el --- Center buffer content horizontally and vertically -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;; This package provides a minor mode `center-content-mode` that centers the visible content
+;; of the current buffer both horizontally and vertically. It calculates the necessary margins
+;; and applies them using overlays and header line adjustments. The mode line is hidden to
+;; provide a clean appearance.
+
+;;; Code:
+
+(defvar-local center-content--horiz-overlay nil
+  "Overlay used by `center-content-mode` to add left margin for horizontal centering.")
+
+(defvar-local center-content--original-header-line-format nil
+  "Stores the original `header-line-format` to restore upon disabling.")
+
+(defvar-local center-content--original-mode-line-format nil
+  "Stores the original `mode-line-format` to restore upon disabling.")
+
+(defface center-content-header-line
+  `((t (:inherit default
+                 :background ,(face-background 'default nil t)
+                 :foreground ,(face-foreground 'default nil t))))
+  "Face for the header line in `center-content-mode`."
+  :group 'center-content)
+
+(defun center-content--calculate-left-margin ()
+  "Calculate the left margin needed to center the content horizontally."
+  (let* ((window (selected-window))
+         (window-width (window-pixel-width window))
+         (content-width (car (window-text-pixel-size
+                              window
+                              (window-start window)
+                              (window-end window))))
+         (space-width (string-pixel-width " "))
+         (margin (/ (max 0 (- window-width content-width)) (* 2 space-width))))
+    margin))
+
+(defun center-content--calculate-top-margin ()
+  "Calculate the top margin needed to center the content vertically."
+  (let* ((window-height (window-pixel-height))
+         (content-height (cdr (window-text-pixel-size)))
+         (margin (/ (max 0 (- window-height content-height)) 2)))
+    margin))
+
+(defun center-content--enable ()
+  "Enable horizontal and vertical centering of content."
+  (let ((left-margin (center-content--calculate-left-margin))
+        (top-margin (center-content--calculate-top-margin)))
+    ;; Apply horizontal centering using overlay
+    (let ((horiz-overlay (make-overlay (point-min) (point-max))))
+      (overlay-put horiz-overlay 'line-prefix
+                   (propertize " " 'display `(space :width ,left-margin)))
+      (setq center-content--horiz-overlay horiz-overlay))
+    ;; Save the original header-line-format
+    (setq center-content--original-header-line-format header-line-format)
+    ;; Apply vertical centering using header-line-format with custom face
+    (setq header-line-format
+          (propertize " "
+                      'display `(height ,(max 0 (/ top-margin (frame-char-height))))
+                      'face 'center-content-header-line))
+    ;; Save the original mode-line-format
+    (setq center-content--original-mode-line-format mode-line-format)
+    ;; Hide the mode line
+    (setq mode-line-format nil)))
+
+(defun center-content--disable ()
+  "Disable centering of content."
+  ;; Remove horizontal centering overlay
+  (when (overlayp center-content--horiz-overlay)
+    (delete-overlay center-content--horiz-overlay)
+    (setq center-content--horiz-overlay nil))
+  ;; Restore the original header-line-format
+  (setq header-line-format center-content--original-header-line-format)
+  (setq center-content--original-header-line-format nil)
+  ;; Restore the original mode-line-format
+  (setq mode-line-format center-content--original-mode-line-format)
+  (setq center-content--original-mode-line-format nil)
+  ;; Force redisplay to remove any lingering effects
+  (force-mode-line-update)
+  (redisplay))
+
+;;;###autoload
+(define-minor-mode center-content-mode
+  "Toggle horizontal and vertical centering of buffer content.
+
+When enabled, the visible content of the buffer is centered both
+horizontally and vertically within the window. The mode line is
+hidden for a clean appearance."
+  :init-value nil
+  :global nil
+  :lighter nil  ;; Remove the lighter to keep the mode line clean
+  (if center-content-mode
+      (center-content--enable)
+    (center-content--disable)))
+
+(provide 'center-content)
+
+;;; center-content.el ends here