/* global AFRAME */
AFRAME.registerShader('skyGradient', {
  schema: {
    colorTop: { type: 'color', default: 'black', is: 'uniform' },
    colorBottom: { type: 'color', default: 'red', is: 'uniform' }
  },

  vertexShader: [
    'varying vec3 vWorldPosition;',

    'void main() {',

      'vec4 worldPosition = modelMatrix * vec4( position, 1.0 );',
      'vWorldPosition = worldPosition.xyz;',

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

    '}'

  ].join('\n'),

  fragmentShader: [
    'uniform vec3 colorTop;',
    'uniform vec3 colorBottom;',

    'varying vec3 vWorldPosition;',

    'void main()',

    '{',
      'vec3 pointOnSphere = normalize(vWorldPosition.xyz);',
      'float f = 1.0;',
      'if(pointOnSphere.y > - 0.2){',

        'f = sin(pointOnSphere.y * 2.0);',

      '}',
      'gl_FragColor = vec4(mix(colorBottom,colorTop, f ), 1.0);',

    '}'
  ].join('\n')
});