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

/**
 * Unpack RGBA depth shader
 * - show RGBA encoded depth as monochrome color
 */

THREE.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 );',

		'}'

	].join( '\n' ),

	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 );',

		'}'

	].join( '\n' )

};