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

/**
 * 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' )

};

export { VignetteShader };