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

/**
 * 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' )

};

export { MirrorShader };