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TiddlyWiki5/core/modules/macros/contrastcolour.js

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/*\
title: $:/core/modules/macros/contrastcolour.js
type: application/javascript
module-type: macro
Macro to choose which of two colours has the highest contrast with a base colour
\*/
(function(){
/*jslint node: true, browser: true */
/*global $tw: false */
"use strict";
/*
Information about this macro
*/
exports.name = "contrastcolour";
exports.params = [
{name: "target"},
{name: "fallbackTarget"},
{name: "colourA"},
{name: "colourB"}
];
/*
Run the macro
*/
exports.run = function(target,fallbackTarget,colourA,colourB) {
var rgbTarget = $tw.utils.parseCSSColor(target) || $tw.utils.parseCSSColor(fallbackTarget);
if(!rgbTarget) {
return colourA;
}
var rgbColourA = $tw.utils.parseCSSColor(colourA),
rgbColourB = $tw.utils.parseCSSColor(colourB);
if(rgbColourA && !rgbColourB) {
return rgbColourA;
}
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if(rgbColourB && !rgbColourA) {
return rgbColourB;
}
if(!rgbColourA && !rgbColourB) {
// If neither colour is readable, return a crude inverse of the target
return [255 - rgbTarget[0],255 - rgbTarget[1],255 - rgbTarget[2],rgbTarget[3]];
}
// Colour brightness formula derived from http://www.w3.org/WAI/ER/WD-AERT/#color-contrast
var brightnessTarget = rgbTarget[0] * 0.299 + rgbTarget[1] * 0.587 + rgbTarget[2] * 0.114,
brightnessA = rgbColourA[0] * 0.299 + rgbColourA[1] * 0.587 + rgbColourA[2] * 0.114,
brightnessB = rgbColourB[0] * 0.299 + rgbColourB[1] * 0.587 + rgbColourB[2] * 0.114;
return Math.abs(brightnessTarget - brightnessA) > Math.abs(brightnessTarget - brightnessB) ? colourA : colourB;
};
})();