three.js/examples/js/shaders/CopyShader.js

( function () {

	/**
 * Full-screen textured quad shader
 */

	const CopyShader = {
		uniforms: {
			'tDiffuse': {
				value: null
			},
			'opacity': {
				value: 1.0
			}
		},
		vertexShader: /* glsl */`

		varying vec2 vUv;

		void main() {

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

		}`,
		fragmentShader: /* glsl */`

		uniform float opacity;

		uniform sampler2D tDiffuse;

		varying vec2 vUv;

		void main() {

			gl_FragColor = texture2D( tDiffuse, vUv );
			gl_FragColor.a *= opacity;


		}`
	};

	THREE.CopyShader = CopyShader;

} )();