three.js/examples/js/postprocessing/ShaderPass.js

( function () {

	var ShaderPass = function ( shader, textureID ) {

		THREE.Pass.call( this );
		this.textureID = textureID !== undefined ? textureID : 'tDiffuse';

		if ( shader instanceof THREE.ShaderMaterial ) {

			this.uniforms = shader.uniforms;
			this.material = shader;

		} else if ( shader ) {

			this.uniforms = THREE.UniformsUtils.clone( shader.uniforms );
			this.material = new THREE.ShaderMaterial( {
				defines: Object.assign( {}, shader.defines ),
				uniforms: this.uniforms,
				vertexShader: shader.vertexShader,
				fragmentShader: shader.fragmentShader
			} );

		}

		this.fsQuad = new THREE.Pass.FullScreenQuad( this.material );

	};

	ShaderPass.prototype = Object.assign( Object.create( THREE.Pass.prototype ), {
		constructor: ShaderPass,
		render: function ( renderer, writeBuffer, readBuffer
			/*, deltaTime, maskActive */
		) {

			if ( this.uniforms[ this.textureID ] ) {

				this.uniforms[ this.textureID ].value = readBuffer.texture;

			}

			this.fsQuad.material = this.material;

			if ( this.renderToScreen ) {

				renderer.setRenderTarget( null );
				this.fsQuad.render( renderer );

			} else {

				renderer.setRenderTarget( writeBuffer ); // TODO: Avoid using autoClear properties, see https://github.com/mrdoob/three.js/pull/15571#issuecomment-465669600

				if ( this.clear ) renderer.clear( renderer.autoClearColor, renderer.autoClearDepth, renderer.autoClearStencil );
				this.fsQuad.render( renderer );

			}

		}
	} );

	THREE.ShaderPass = ShaderPass;

} )();