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