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)
 */

const MirrorShader = {

	name: 'MirrorShader',

	uniforms: {

		'tDiffuse': { value: null },
		'side': { value: 1 }

	},

	vertexShader: /* glsl */`

		varying vec2 vUv;

		void main() {

			vUv = uv;
			gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );

		}`,

	fragmentShader: /* glsl */`

		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;

		}`

};

export { MirrorShader };