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 alpha blended sum is used.
31 (defun colir-join (r g b)
32 "Build a color from R G B.
33 Inverse of `color-values'."
34 (format "#%02x%02x%02x"
39 (defun colir-blend (c1 c2 &optional alpha)
40 "Blend the two colors C1 and C2 with ALPHA.
41 C1 and C2 are in the format of `color-values'.
42 ALPHA is a number between 0.0 and 1.0 which corresponds to the
43 influence of C1 on the result."
44 (setq alpha (or alpha 0.5))
48 (round (+ (* x alpha) (* y (- 1 alpha)))))
51 (defun colir-blend-face-background (start end face &optional object)
52 "Append to the face property of the text from START to END the face FACE.
53 When the text already has a face with a non-plain background,
54 blend it with the background of FACE.
55 Optional argument OBJECT is the string or buffer containing the text.
56 See also `font-lock-append-text-property'."
59 (setq next (next-single-property-change start 'face object end)
60 prev (get-text-property start 'face object))
62 (let ((background-prev (face-background prev)))
67 (cons `(background-color
69 (color-values background-prev)
70 (color-values (face-background face nil t))))
74 (put-text-property start next 'face face object))
79 ;;; colir.el ends here