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 };