three.js/examples/js/shaders/MirrorShader.js

( function () {

	/**
 * Mirror Shader
 * Copies half the input to the other half
 *
 * side: side of input to mirror (0 = left, 1 = right, 2 = top, 3 = bottom)
 */
	var MirrorShader = {
		uniforms: {
			'tDiffuse': {
				value: null
			},
			'side': {
				value: 1
			}
		},
		vertexShader: [ 'varying vec2 vUv;', 'void main() {', '	vUv = uv;', '	gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );', '}' ].join( '\n' ),
		fragmentShader: [ 'uniform sampler2D tDiffuse;', 'uniform int side;', 'varying vec2 vUv;', 'void main() {', '	vec2 p = vUv;', '	if (side == 0){', '		if (p.x > 0.5) p.x = 1.0 - p.x;', '	}else if (side == 1){', '		if (p.x < 0.5) p.x = 1.0 - p.x;', '	}else if (side == 2){', '		if (p.y < 0.5) p.y = 1.0 - p.y;', '	}else if (side == 3){', '		if (p.y > 0.5) p.y = 1.0 - p.y;', '	} ', '	vec4 color = texture2D(tDiffuse, p);', '	gl_FragColor = color;', '}' ].join( '\n' )
	};

	THREE.MirrorShader = MirrorShader;

} )();