1 ;;; colir.el --- Color blending library -*- lexical-binding: t -*-
3 ;; Copyright (C) 2015 Free Software Foundation, Inc.
5 ;; Author: Oleh Krehel <ohwoeowho@gmail.com>
7 ;; This file is part of GNU Emacs.
9 ;; This file is free software; you can redistribute it and/or modify
10 ;; it under the terms of the GNU General Public License as published by
11 ;; the Free Software Foundation; either version 3, or (at your option)
14 ;; This program is distributed in the hope that it will be useful,
15 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
16 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 ;; GNU General Public License for more details.
19 ;; For a full copy of the GNU General Public License
20 ;; see <http://www.gnu.org/licenses/>.
24 ;; This package solves the problem of adding a face with a background
25 ;; to text which may already have a background. In all conflicting
26 ;; areas, instead of choosing either the original or the new
27 ;; background face, their blended sum is used.
29 ;; The blend mode functions are taken from http://en.wikipedia.org/wiki/Blend_modes.
35 (defcustom colir-compose-method 'colir-compose-alpha
36 "Select a method to compose two color channels."
38 (const colir-compose-alpha)
39 (const colir-compose-overlay)
40 (const colir-compose-soft-light))
43 (defun colir-compose-soft-light (a b)
44 "Compose A and B channels."
46 (+ (* 2 a b) (* a a (- 1 b b)))
47 (+ (* 2 a (- 1 b)) (* (sqrt a) (- (* 2 b) 1)))))
49 (defun colir-compose-overlay (a b)
50 "Compose A and B channels."
53 (- 1 (* 2 (- 1 a) (- 1 b)))))
55 (defun colir-compose-alpha (a b &optional alpha gamma)
56 "Compose A and B channels."
57 (setq alpha (or alpha 0.5))
58 (setq gamma (or gamma 2.2))
59 (+ (* (expt a gamma) alpha) (* (expt b gamma) (- 1 alpha))))
61 (defun colir-blend (c1 c2)
62 "Blend the two colors C1 and C2 using `colir-compose-method'.
63 C1 and C2 are triples of floats in [0.0 1.0] range."
64 (apply #'color-rgb-to-hex
69 (defun colir-blend-face-background (start end face &optional object)
70 "Append to the face property of the text from START to END the face FACE.
71 When the text already has a face with a non-plain background,
72 blend it with the background of FACE.
73 Optional argument OBJECT is the string or buffer containing the text.
74 See also `font-lock-append-text-property'."
77 (setq next (next-single-property-change start 'face object end)
78 prev (get-text-property start 'face object))
80 (setq prev (cl-find-if #'atom prev)))
82 (let ((background-prev (face-background prev)))
87 (cons `(background-color
89 (color-name-to-rgb background-prev)
90 (color-name-to-rgb (face-background face nil t))))
94 (put-text-property start next 'face face object))
99 ;;; colir.el ends here