three.js/examples/jsm/postprocessing/LUTPass.js

import { ShaderPass } from './ShaderPass.js';

const LUTShader = {

	defines: {
		USE_3DTEXTURE: 1,
	},

	uniforms: {
		lut3d: { value: null },

		lut: { value: null },
		lutSize: { value: 0 },

		tDiffuse: { value: null },
		intensity: { value: 1.0 },
	},

	vertexShader: /* glsl */`

		varying vec2 vUv;

		void main() {

			vUv = uv;
			gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );

		}

	`,


	fragmentShader: /* glsl */`
		precision highp sampler3D;

		#if USE_3DTEXTURE
		uniform sampler3D lut3d;
		#else
		uniform sampler2D lut;
		uniform float lutSize;

		vec3 lutLookup( sampler2D tex, float size, vec3 rgb ) {

			// clamp the sample in by half a pixel to avoid interpolation
			// artifacts between slices laid out next to each other.
			float halfPixelWidth = 0.5 / size;
			rgb.rg = clamp( rgb.rg, halfPixelWidth, 1.0 - halfPixelWidth );

			// green offset into a LUT layer
			float gOffset = rgb.g / size;
			vec2 uv1 = vec2( rgb.r, gOffset );
			vec2 uv2 = vec2( rgb.r, gOffset );

			// adjust b slice offset
			float bNormalized = size * rgb.b;
			float bSlice = min( floor( size * rgb.b ), size - 1.0 );
			float bMix = ( bNormalized - bSlice ) / size;

			// get the first lut slice and then the one to interpolate to
			float b1 = bSlice / size;
			float b2 = ( bSlice + 1.0 ) / size;

			uv1.y += b1;
			uv2.y += b2;

			vec3 sample1 = texture2D( tex, uv1 ).rgb;
			vec3 sample2 = texture2D( tex, uv2 ).rgb;

			return mix( sample1, sample2, bMix );

		}
		#endif

		varying vec2 vUv;
		uniform float intensity;
		uniform sampler2D tDiffuse;
		void main() {

			vec4 val = texture2D( tDiffuse, vUv );
			vec4 lutVal;
			#if USE_3DTEXTURE
			lutVal = vec4( texture( lut3d, val.rgb ).rgb, val.a );
			#else
			lutVal = vec4( lutLookup( lut, lutSize, val.rgb ), val.a );
			#endif
			gl_FragColor = mix( val, lutVal, intensity );

		}

	`,

};

class LUTPass extends ShaderPass {

	set lut( v ) {

		const material = this.material;
		if ( v !== this.lut ) {

			material.uniforms.lut3d.value = null;
			material.uniforms.lut.value = null;

			if ( v ) {

				const is3dTextureDefine = v.isDataTexture3D ? 1 : 0;
				if ( is3dTextureDefine !== material.defines.USE_3DTEXTURE ) {

					material.defines.USE_3DTEXTURE = is3dTextureDefine;
					material.needsUpdate = true;

				}

				if ( v.isDataTexture3D ) {

					material.uniforms.lut3d.value = v;

				} else {

					material.uniforms.lut.value = v;
					material.uniforms.lutSize.value = v.image.width;

				}

			}

		}

	}

	get lut() {

		return this.material.uniforms.lut.value || this.material.uniforms.lut3d.value;

	}

	set intensity( v ) {

		this.material.uniforms.intensity.value = v;

	}

	get intensity() {

		return this.material.uniforms.intensity.value;

	}

	constructor( options = {} ) {

		super( LUTShader );
		this.lut = options.lut || null;
		this.intensity = 'intensity' in options ? options.intensity : 1;

	}

}

export { LUTPass };