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https://github.com/Jermolene/TiddlyWiki5
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56 lines
1.5 KiB
JavaScript
56 lines
1.5 KiB
JavaScript
/*\
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title: $:/core/modules/macros/contrastcolour.js
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type: application/javascript
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module-type: macro
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Macro to choose which of two colours has the highest contrast with a base colour
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\*/
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(function(){
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/*jslint node: true, browser: true */
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/*global $tw: false */
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"use strict";
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/*
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Information about this macro
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*/
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exports.name = "contrastcolour";
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exports.params = [
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{name: "target"},
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{name: "fallbackTarget"},
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{name: "colourA"},
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{name: "colourB"}
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];
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/*
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Run the macro
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*/
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exports.run = function(target,fallbackTarget,colourA,colourB) {
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var rgbTarget = $tw.utils.parseCSSColor(target) || $tw.utils.parseCSSColor(fallbackTarget);
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if(!rgbTarget) {
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return colourA;
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}
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var rgbColourA = $tw.utils.parseCSSColor(colourA),
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rgbColourB = $tw.utils.parseCSSColor(colourB);
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if(rgbColourA && !rgbColourB) {
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return rgbColourA;
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}
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if(rgbColourB && !rgbColourA) {
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return rgbColourB;
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}
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if(!rgbColourA && !rgbColourB) {
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// If neither colour is readable, return a crude inverse of the target
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return [255 - rgbTarget[0],255 - rgbTarget[1],255 - rgbTarget[2],rgbTarget[3]];
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}
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// Colour brightness formula derived from http://www.w3.org/WAI/ER/WD-AERT/#color-contrast
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var brightnessTarget = rgbTarget[0] * 0.299 + rgbTarget[1] * 0.587 + rgbTarget[2] * 0.114,
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brightnessA = rgbColourA[0] * 0.299 + rgbColourA[1] * 0.587 + rgbColourA[2] * 0.114,
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brightnessB = rgbColourB[0] * 0.299 + rgbColourB[1] * 0.587 + rgbColourB[2] * 0.114;
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return Math.abs(brightnessTarget - brightnessA) > Math.abs(brightnessTarget - brightnessB) ? colourA : colourB;
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};
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})();
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