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|
;;; colir.el --- Color blending library -*- lexical-binding: t -*-
;; Copyright (C) 2015-2018 Free Software Foundation, Inc.
;; Author: Oleh Krehel <ohwoeowho@gmail.com>
;; This file is part of GNU Emacs.
;; This file is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 3, or (at your option)
;; any later version.
;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU General Public License for more details.
;; For a full copy of the GNU General Public License
;; see <http://www.gnu.org/licenses/>.
;;; Commentary:
;; This package solves the problem of adding a face with a background
;; to text which may already have a background. In all conflicting
;; areas, instead of choosing either the original or the new
;; background face, their blended sum is used.
;;
;; The blend mode functions are taken from URL
;; `http://en.wikipedia.org/wiki/Blend_modes'.
;;; Code:
(require 'cl-lib)
(require 'color)
(defcustom colir-compose-method #'colir-compose-alpha
"Select a method to compose two color channels."
:group 'ivy
:type '(radio
(function-item colir-compose-alpha)
(function-item colir-compose-overlay)
(function-item colir-compose-soft-light)))
(defun colir-compose-soft-light (a b)
"Compose A and B channels."
(if (< b 0.5)
(+ (* 2 a b) (* a a (- 1 b b)))
(+ (* 2 a (- 1 b)) (* (sqrt a) (- (* 2 b) 1)))))
(defun colir-compose-overlay (a b)
"Compose A and B channels."
(if (< a 0.5)
(* 2 a b)
(- 1 (* 2 (- 1 a) (- 1 b)))))
(defun colir-compose-alpha (a b &optional alpha gamma)
"Compose A and B channels.
Optional argument ALPHA is a number between 0.0 and 1.0 which corresponds
to the influence of A on the result. Default value is 0.5.
Optional argument GAMMA is used for gamma correction. Default value is 2.2."
(setq alpha (or alpha 0.5))
(setq gamma (or gamma 2.2))
(+ (* (expt a gamma) alpha) (* (expt b gamma) (- 1 alpha))))
(defun colir-blend (c1 c2)
"Blend the two colors C1 and C2 using `colir-compose-method'.
C1 and C2 are triples of floats in [0.0 1.0] range."
(apply #'color-rgb-to-hex
(cl-mapcar
(if (eq (frame-parameter nil 'background-mode) 'dark)
;; this method works nicely for dark themes
'colir-compose-soft-light
colir-compose-method)
c1 c2)))
(defun colir-color-parse (color)
"Convert string COLOR to triple of floats in [0.0 1.0]."
(if (string-match "#\\([[:xdigit:]]\\{2\\}\\)\\([[:xdigit:]]\\{2\\}\\)\\([[:xdigit:]]\\{2\\}\\)" color)
(mapcar (lambda (v) (/ (string-to-number v 16) 255.0))
(list (match-string 1 color) (match-string 2 color) (match-string 3 color)))
;; does not work properly in terminal (maps color to nearest color
;; from available color palette).
(color-name-to-rgb color)))
(defun colir--blend-background (start next prevn face object)
(let ((background-prev (face-background prevn)))
(progn
(put-text-property
start next 'face
(if background-prev
(cons `(background-color
. ,(colir-blend
(colir-color-parse background-prev)
(colir-color-parse (face-background face nil t))))
prevn)
(list face prevn))
object))))
(defun colir-blend-face-background (start end face &optional object)
"Append to the face property of the text from START to END the face FACE.
When the text already has a face with a non-plain background,
blend it with the background of FACE.
Optional argument OBJECT is the string or buffer containing the text.
See also `font-lock-append-text-property'."
(let (next prev prevn)
(while (/= start end)
(setq next (next-single-property-change start 'face object end))
(setq prev (get-text-property start 'face object))
(setq prevn (if (listp prev)
(cl-find-if #'atom prev)
prev))
(cond
((or (keywordp (car-safe prev)) (consp (car-safe prev)))
(put-text-property start next 'face (cons face prev) object))
((facep prevn)
(colir--blend-background start next prevn face object))
(t
(put-text-property start next 'face face object)))
(setq start next))))
(provide 'colir)
;;; colir.el ends here
|
