threejs/examples/js/math/Lut.js

( function () {

	class Lut {

		constructor( colormap, count = 32 ) {

			this.isLut = true;
			this.lut = [];
			this.map = [];
			this.n = 0;
			this.minV = 0;
			this.maxV = 1;
			this.setColorMap( colormap, count );

		}
		set( value ) {

			if ( value.isLut === true ) {

				this.copy( value );

			}

			return this;

		}
		setMin( min ) {

			this.minV = min;
			return this;

		}
		setMax( max ) {

			this.maxV = max;
			return this;

		}
		setColorMap( colormap, count = 32 ) {

			this.map = ColorMapKeywords[ colormap ] || ColorMapKeywords.rainbow;
			this.n = count;
			const step = 1.0 / this.n;
			const minColor = new THREE.Color();
			const maxColor = new THREE.Color();
			this.lut.length = 0;

			// sample at 0

			this.lut.push( new THREE.Color( this.map[ 0 ][ 1 ] ) );

			// sample at 1/n, ..., (n-1)/n

			for ( let i = 1; i < count; i ++ ) {

				const alpha = i * step;
				for ( let j = 0; j < this.map.length - 1; j ++ ) {

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

						const min = this.map[ j ][ 0 ];
						const max = this.map[ j + 1 ][ 0 ];
						minColor.set( this.map[ j ][ 1 ] );
						maxColor.set( this.map[ j + 1 ][ 1 ] );
						const color = new THREE.Color().lerpColors( minColor, maxColor, ( alpha - min ) / ( max - min ) );
						this.lut.push( color );

					}

				}

			}

			// sample at 1

			this.lut.push( new THREE.Color( this.map[ this.map.length - 1 ][ 1 ] ) );
			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 ) {

			alpha = THREE.MathUtils.clamp( alpha, this.minV, this.maxV );
			alpha = ( alpha - this.minV ) / ( this.maxV - this.minV );
			const colorPosition = Math.round( alpha * this.n );
			return this.lut[ colorPosition ];

		}
		addColorMap( name, arrayOfColors ) {

			ColorMapKeywords[ name ] = arrayOfColors;
			return this;

		}
		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;
			const minColor = new THREE.Color();
			const maxColor = new THREE.Color();
			const finalColor = new THREE.Color();
			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 ];
						minColor.set( this.map[ j - 1 ][ 1 ] );
						maxColor.set( this.map[ j ][ 1 ] );
						finalColor.lerpColors( minColor, maxColor, ( i - min ) / ( max - min ) );
						data[ k * 4 ] = Math.round( finalColor.r * 255 );
						data[ k * 4 + 1 ] = Math.round( finalColor.g * 255 );
						data[ k * 4 + 2 ] = Math.round( finalColor.b * 255 );
						data[ k * 4 + 3 ] = 255;
						k += 1;

					}

				}

			}

			ctx.putImageData( imageData, 0, 0 );
			return canvas;

		}

	}
	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 ]]
	};

	THREE.ColorMapKeywords = ColorMapKeywords;
	THREE.Lut = Lut;

} )();