144 lines
3.3 KiB
JavaScript
144 lines
3.3 KiB
JavaScript
/*
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* Ben Postlethwaite
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* January 2013
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* License MIT
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*/
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'use strict';
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var colorScale = require('./colorScale');
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var lerp = require('lerp')
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module.exports = createColormap;
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function createColormap (spec) {
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/*
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* Default Options
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*/
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var indicies, fromrgba, torgba,
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nsteps, cmap, colormap, format,
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nshades, colors, alpha, i;
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if ( !spec ) spec = {};
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nshades = (spec.nshades || 72) - 1;
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format = spec.format || 'hex';
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colormap = spec.colormap;
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if (!colormap) colormap = 'jet';
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if (typeof colormap === 'string') {
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colormap = colormap.toLowerCase();
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if (!colorScale[colormap]) {
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throw Error(colormap + ' not a supported colorscale');
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}
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cmap = colorScale[colormap];
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} else if (Array.isArray(colormap)) {
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cmap = colormap.slice();
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} else {
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throw Error('unsupported colormap option', colormap);
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}
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if (cmap.length > nshades + 1) {
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throw new Error(
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colormap+' map requires nshades to be at least size '+cmap.length
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);
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}
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if (!Array.isArray(spec.alpha)) {
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if (typeof spec.alpha === 'number') {
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alpha = [spec.alpha, spec.alpha];
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} else {
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alpha = [1, 1];
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}
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} else if (spec.alpha.length !== 2) {
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alpha = [1, 1];
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} else {
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alpha = spec.alpha.slice();
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}
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// map index points from 0..1 to 0..n-1
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indicies = cmap.map(function(c) {
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return Math.round(c.index * nshades);
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});
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// Add alpha channel to the map
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alpha[0] = Math.min(Math.max(alpha[0], 0), 1);
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alpha[1] = Math.min(Math.max(alpha[1], 0), 1);
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var steps = cmap.map(function(c, i) {
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var index = cmap[i].index
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var rgba = cmap[i].rgb.slice();
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// if user supplies their own map use it
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if (rgba.length === 4 && rgba[3] >= 0 && rgba[3] <= 1) {
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return rgba
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}
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rgba[3] = alpha[0] + (alpha[1] - alpha[0])*index;
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return rgba
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})
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/*
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* map increasing linear values between indicies to
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* linear steps in colorvalues
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*/
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var colors = []
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for (i = 0; i < indicies.length-1; ++i) {
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nsteps = indicies[i+1] - indicies[i];
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fromrgba = steps[i];
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torgba = steps[i+1];
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for (var j = 0; j < nsteps; j++) {
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var amt = j / nsteps
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colors.push([
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Math.round(lerp(fromrgba[0], torgba[0], amt)),
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Math.round(lerp(fromrgba[1], torgba[1], amt)),
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Math.round(lerp(fromrgba[2], torgba[2], amt)),
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lerp(fromrgba[3], torgba[3], amt)
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])
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}
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}
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//add 1 step as last value
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colors.push(cmap[cmap.length - 1].rgb.concat(alpha[1]))
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if (format === 'hex') colors = colors.map( rgb2hex );
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else if (format === 'rgbaString') colors = colors.map( rgbaStr );
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else if (format === 'float') colors = colors.map( rgb2float );
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return colors;
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};
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function rgb2float (rgba) {
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return [
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rgba[0] / 255,
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rgba[1] / 255,
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rgba[2] / 255,
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rgba[3]
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]
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}
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function rgb2hex (rgba) {
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var dig, hex = '#';
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for (var i = 0; i < 3; ++i) {
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dig = rgba[i];
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dig = dig.toString(16);
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hex += ('00' + dig).substr( dig.length );
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}
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return hex;
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}
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function rgbaStr (rgba) {
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return 'rgba(' + rgba.join(',') + ')';
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}
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