three.js/examples/js/shaders/UnpackDepthRGBAShader.js

( function () {

	/**
 * Unpack RGBA depth shader
 * - show RGBA encoded depth as monochrome color
 */
	const UnpackDepthRGBAShader = {
		uniforms: {
			'tDiffuse': {
				value: null
			},
			'opacity': {
				value: 1.0
			}
		},
		vertexShader: `varying vec2 vUv;

		void main() {

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

		}`,
		fragmentShader: `uniform float opacity;

		uniform sampler2D tDiffuse;

		varying vec2 vUv;

		#include <packing>

		void main() {

			float depth = 1.0 - unpackRGBAToDepth( texture2D( tDiffuse, vUv ) );
			gl_FragColor = vec4( vec3( depth ), opacity );

		}`
	};

	THREE.UnpackDepthRGBAShader = UnpackDepthRGBAShader;

} )();