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let vertexShader = `
    varying vec3 vPos;
    void main()	{
      vPos = position;
      gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
    }`;

let fragmentShader = `
    varying vec3 vPos;
    uniform vec3 size;
    uniform float thickness;
    uniform float smoothness;

    void main() {
      float a = smoothstep(thickness, thickness + smoothness, length(abs(vPos.xy) - size.xy));
      a *= smoothstep(thickness, thickness + smoothness, length(abs(vPos.yz) - size.yz));
      a *= smoothstep(thickness, thickness + smoothness, length(abs(vPos.xz) - size.xz));

      vec3 c = mix(vec3(0,0,0), vec3(1,1,1), a);

      gl_FragColor = vec4(c, 1.0);
    }`;