three.js/examples/js/shaders/NormalMapShader.js

/**
 * Normal map shader
 * - compute normals from heightmap
 */

THREE.NormalMapShader = {

	uniforms: {

		'heightMap': { value: null },
		'resolution': { value: new THREE.Vector2( 512, 512 ) },
		'scale': { value: new THREE.Vector2( 1, 1 ) },
		'height': { value: 0.05 }

	},

	vertexShader: [

		'varying vec2 vUv;',

		'void main() {',

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

		'}'

	].join( '\n' ),

	fragmentShader: [

		'uniform float height;',
		'uniform vec2 resolution;',
		'uniform sampler2D heightMap;',

		'varying vec2 vUv;',

		'void main() {',

		'	float val = texture2D( heightMap, vUv ).x;',

		'	float valU = texture2D( heightMap, vUv + vec2( 1.0 / resolution.x, 0.0 ) ).x;',
		'	float valV = texture2D( heightMap, vUv + vec2( 0.0, 1.0 / resolution.y ) ).x;',

		'	gl_FragColor = vec4( ( 0.5 * normalize( vec3( val - valU, val - valV, height  ) ) + 0.5 ), 1.0 );',

		'}'

	].join( '\n' )

};