text: const vs = `
  precision highp float;
  
  attribute vec3 position;
  attribute vec3 normal;
  
  uniform mat4 modelViewMatrix;
  uniform mat4 projectionMatrix;
  uniform mat4 modelMatrix;
  uniform mat3 normalMatrix;
  
  uniform float spread;
  
  varying float vRim;
  
  void main() {
    vec3 e = normalize( vec3( modelViewMatrix * vec4( position, 1.0 ) ) );
    vec3 n = normalize( normalMatrix * normal );
    vRim = 50.*position.z * pow(abs(dot(e,n)),spread);
    vec4 mvPosition = modelViewMatrix * vec4( position, 1.0 );
    gl_Position = projectionMatrix * mvPosition;
  }
  `;
  
  export { vs };