three.js/examples/jsm/math/Lut.js

import {
	Color
} from '../../../build/three.module.js';

class Lut {

 	constructor( colormap, numberofcolors ) {

		this.lut = [];
		this.setColorMap( colormap, numberofcolors );

	}

	set( value ) {

		if ( value instanceof Lut ) {

			this.copy( value );

		}

		return this;

	}

	setMin( min ) {

		this.minV = min;

		return this;

	}

	setMax( max ) {

		this.maxV = max;

		return this;

	}

	setColorMap( colormap, numberofcolors = 32 ) {

		this.map = ColorMapKeywords[ colormap ] || ColorMapKeywords.rainbow;
		this.n = numberofcolors;

		const step = 1.0 / this.n;

		this.lut.length = 0;

		for ( let i = 0; i <= 1; i += step ) {

			for ( let j = 0; j < this.map.length - 1; j ++ ) {

				if ( i >= this.map[ j ][ 0 ] && i < this.map[ j + 1 ][ 0 ] ) {

					const min = this.map[ j ][ 0 ];
					const max = this.map[ j + 1 ][ 0 ];

					const minColor = new Color( this.map[ j ][ 1 ] );
					const maxColor = new Color( this.map[ j + 1 ][ 1 ] );

					const color = minColor.lerp( maxColor, ( i - min ) / ( max - min ) );

					this.lut.push( color );

				}

			}

		}

		return this;

	}

	copy( lut ) {

		this.lut = lut.lut;
		this.map = lut.map;
		this.n = lut.n;
		this.minV = lut.minV;
		this.maxV = lut.maxV;

		return this;

	}

	getColor( alpha ) {

		if ( alpha <= this.minV ) {

			alpha = this.minV;

		} else if ( alpha >= this.maxV ) {

			alpha = this.maxV;

		}

		alpha = ( alpha - this.minV ) / ( this.maxV - this.minV );

		let colorPosition = Math.round( alpha * this.n );
		colorPosition == this.n ? colorPosition -= 1 : colorPosition;

		return this.lut[ colorPosition ];

	}

	addColorMap( colormapName, arrayOfColors ) {

		ColorMapKeywords[ colormapName ] = arrayOfColors;

	}

	createCanvas() {

		const canvas = document.createElement( 'canvas' );
		canvas.width = 1;
		canvas.height = this.n;

		this.updateCanvas( canvas );

		return canvas;

	}

	updateCanvas( canvas ) {

		const ctx = canvas.getContext( '2d', { alpha: false } );

		const imageData = ctx.getImageData( 0, 0, 1, this.n );

		const data = imageData.data;

		let k = 0;

		const step = 1.0 / this.n;

		for ( let i = 1; i >= 0; i -= step ) {

			for ( let j = this.map.length - 1; j >= 0; j -- ) {

				if ( i < this.map[ j ][ 0 ] && i >= this.map[ j - 1 ][ 0 ] ) {

					const min = this.map[ j - 1 ][ 0 ];
					const max = this.map[ j ][ 0 ];

					const minColor = new Color( this.map[ j - 1 ][ 1 ] );
					const maxColor = new Color( this.map[ j ][ 1 ] );

					const color = minColor.lerp( maxColor, ( i - min ) / ( max - min ) );

					data[ k * 4 ] = Math.round( color.r * 255 );
					data[ k * 4 + 1 ] = Math.round( color.g * 255 );
					data[ k * 4 + 2 ] = Math.round( color.b * 255 );
					data[ k * 4 + 3 ] = 255;

					k += 1;

				}

			}

		}

		ctx.putImageData( imageData, 0, 0 );

		return canvas;

	}

}

Lut.prototype.lut = [];
Lut.prototype.map = [];
Lut.prototype.n = 256;
Lut.prototype.minV = 0;
Lut.prototype.maxV = 1;

const ColorMapKeywords = {

	'rainbow': [[ 0.0, 0x0000FF ], [ 0.2, 0x00FFFF ], [ 0.5, 0x00FF00 ], [ 0.8, 0xFFFF00 ], [ 1.0, 0xFF0000 ]],
	'cooltowarm': [[ 0.0, 0x3C4EC2 ], [ 0.2, 0x9BBCFF ], [ 0.5, 0xDCDCDC ], [ 0.8, 0xF6A385 ], [ 1.0, 0xB40426 ]],
	'blackbody': [[ 0.0, 0x000000 ], [ 0.2, 0x780000 ], [ 0.5, 0xE63200 ], [ 0.8, 0xFFFF00 ], [ 1.0, 0xFFFFFF ]],
	'grayscale': [[ 0.0, 0x000000 ], [ 0.2, 0x404040 ], [ 0.5, 0x7F7F80 ], [ 0.8, 0xBFBFBF ], [ 1.0, 0xFFFFFF ]]

};

export { Lut, ColorMapKeywords };