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124 lines
4.5 KiB
124 lines
4.5 KiB
;;; colir.el --- Color blending library -*- lexical-binding: t -*-
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;; Copyright (C) 2015-2019 Free Software Foundation, Inc.
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;; Author: Oleh Krehel <ohwoeowho@gmail.com>
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;; This file is part of GNU Emacs.
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;; This file is free software; you can redistribute it and/or modify
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;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation; either version 3, or (at your option)
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;; any later version.
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;; This program is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;; GNU General Public License for more details.
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;; For a full copy of the GNU General Public License
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;; see <https://www.gnu.org/licenses/>.
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;;; Commentary:
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;; This package solves the problem of adding a face with a background
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;; to text which may already have a background. In all conflicting
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;; areas, instead of choosing either the original or the new
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;; background face, their blended sum is used.
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;;
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;; The blend mode functions are taken from URL
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;; `https://en.wikipedia.org/wiki/Blend_modes'.
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;;; Code:
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(require 'cl-lib)
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(require 'color)
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(defcustom colir-compose-method #'colir-compose-alpha
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"Select a method to compose two color channels."
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:group 'ivy
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:type '(radio
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(function-item colir-compose-alpha)
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(function-item colir-compose-overlay)
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(function-item colir-compose-soft-light)))
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(defun colir-compose-soft-light (a b)
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"Compose A and B channels."
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(if (< b 0.5)
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(+ (* 2 a b) (* a a (- 1 b b)))
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(+ (* 2 a (- 1 b)) (* (sqrt a) (- (* 2 b) 1)))))
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(defun colir-compose-overlay (a b)
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"Compose A and B channels."
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(if (< a 0.5)
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(* 2 a b)
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(- 1 (* 2 (- 1 a) (- 1 b)))))
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(defun colir-compose-alpha (a b &optional alpha gamma)
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"Compose A and B channels.
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Optional argument ALPHA is a number between 0.0 and 1.0 which corresponds
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to the influence of A on the result. Default value is 0.5.
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Optional argument GAMMA is used for gamma correction. Default value is 2.2."
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(setq alpha (or alpha 0.5))
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(setq gamma (or gamma 2.2))
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(+ (* (expt a gamma) alpha) (* (expt b gamma) (- 1 alpha))))
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(defun colir-blend (c1 c2)
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"Blend the two colors C1 and C2 using `colir-compose-method'.
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C1 and C2 are triples of floats in [0.0 1.0] range."
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(apply #'color-rgb-to-hex
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(cl-mapcar
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(if (eq (frame-parameter nil 'background-mode) 'dark)
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;; this method works nicely for dark themes
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'colir-compose-soft-light
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colir-compose-method)
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c1 c2)))
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(defun colir-color-parse (color)
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"Convert string COLOR to triple of floats in [0.0 1.0]."
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(if (string-match "#\\([[:xdigit:]]\\{2\\}\\)\\([[:xdigit:]]\\{2\\}\\)\\([[:xdigit:]]\\{2\\}\\)" color)
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(mapcar (lambda (v) (/ (string-to-number v 16) 255.0))
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(list (match-string 1 color) (match-string 2 color) (match-string 3 color)))
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;; does not work properly in terminal (maps color to nearest color
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;; from available color palette).
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(color-name-to-rgb color)))
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(defun colir--blend-background (start next prevn face object)
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(let ((background-prev (face-background prevn)))
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(progn
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(put-text-property
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start next 'face
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(if background-prev
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(cons `(background-color
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. ,(colir-blend
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(colir-color-parse background-prev)
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(colir-color-parse (face-background face nil t))))
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prevn)
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(list face prevn))
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object))))
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(defun colir-blend-face-background (start end face &optional object)
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"Append to the face property of the text from START to END the face FACE.
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When the text already has a face with a non-plain background,
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blend it with the background of FACE.
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Optional argument OBJECT is the string or buffer containing the text.
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See also `font-lock-append-text-property'."
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(let (next prev prevn)
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(while (/= start end)
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(setq next (next-single-property-change start 'face object end))
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(setq prev (get-text-property start 'face object))
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(setq prevn (if (listp prev)
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(cl-find-if #'atom prev)
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prev))
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(cond
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((or (keywordp (car-safe prev)) (consp (car-safe prev)))
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(put-text-property start next 'face (cons face prev) object))
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((facep prevn)
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(colir--blend-background start next prevn face object))
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(t
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(put-text-property start next 'face face object)))
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(setq start next))))
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(provide 'colir)
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;;; colir.el ends here
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