Threejs mirror shader. Splits screen into four. Use in shaderpass

FragmentShader.fs

uniform sampler2D tDiffuse;
		varying vec2 vUv;

    float map(float value, float min1, float max1, float min2, float max2) {
      return min2 + (value - min1) * (max2 - min2) / (max1 - min1);
    }
    
		void main() {
      vec2 doubleUv = vUv * 2.0;

      if(vUv.x > 0.5) doubleUv.x = map(doubleUv.x - 1.0, 0.0, 1.0, 1.0, 0.0);
      
      if (vUv.y > 0.5) doubleUv.y = map(doubleUv.y - 1.0, 0.0, 1.0, 1.0, 0.0);

			gl_FragColor = texture2D(tDiffuse, doubleUv);
		}