three.js/examples/js/shaders/VignetteShader.js

( function () {

	/**
 * Vignette shader
 * based on PaintEffect postprocess from ro.me
 * http://code.google.com/p/3-dreams-of-black/source/browse/deploy/js/effects/PaintEffect.js
 */
	var VignetteShader = {
		uniforms: {
			'tDiffuse': {
				value: null
			},
			'offset': {
				value: 1.0
			},
			'darkness': {
				value: 1.0
			}
		},
		vertexShader: [ 'varying vec2 vUv;', 'void main() {', '	vUv = uv;', '	gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );', '}' ].join( '\n' ),
		fragmentShader: [ 'uniform float offset;', 'uniform float darkness;', 'uniform sampler2D tDiffuse;', 'varying vec2 vUv;', 'void main() {', // Eskil's vignette
			'	vec4 texel = texture2D( tDiffuse, vUv );', '	vec2 uv = ( vUv - vec2( 0.5 ) ) * vec2( offset );', '	gl_FragColor = vec4( mix( texel.rgb, vec3( 1.0 - darkness ), dot( uv, uv ) ), texel.a );',
			/*
	// alternative version from glfx.js
	// this one makes more "dusty" look (as opposed to "burned")
		"	vec4 color = texture2D( tDiffuse, vUv );",
	"	float dist = distance( vUv, vec2( 0.5 ) );",
	"	color.rgb *= smoothstep( 0.8, offset * 0.799, dist *( darkness + offset ) );",
	"	gl_FragColor = color;",
	*/
			'}' ].join( '\n' )
	};

	THREE.VignetteShader = VignetteShader;

} )();