/**
 * Based on Nvidia Cg tutorial
 */

var FresnelShader = {

	uniforms: {

		'mRefractionRatio': { value: 1.02 },
		'mFresnelBias': { value: 0.1 },
		'mFresnelPower': { value: 2.0 },
		'mFresnelScale': { value: 1.0 },
		'tCube': { value: null }

	},

	vertexShader: [

		'uniform float mRefractionRatio;',
		'uniform float mFresnelBias;',
		'uniform float mFresnelScale;',
		'uniform float mFresnelPower;',

		'varying vec3 vReflect;',
		'varying vec3 vRefract[3];',
		'varying float vReflectionFactor;',

		'void main() {',

		'	vec4 mvPosition = modelViewMatrix * vec4( position, 1.0 );',
		'	vec4 worldPosition = modelMatrix * vec4( position, 1.0 );',

		'	vec3 worldNormal = normalize( mat3( modelMatrix[0].xyz, modelMatrix[1].xyz, modelMatrix[2].xyz ) * normal );',

		'	vec3 I = worldPosition.xyz - cameraPosition;',

		'	vReflect = reflect( I, worldNormal );',
		'	vRefract[0] = refract( normalize( I ), worldNormal, mRefractionRatio );',
		'	vRefract[1] = refract( normalize( I ), worldNormal, mRefractionRatio * 0.99 );',
		'	vRefract[2] = refract( normalize( I ), worldNormal, mRefractionRatio * 0.98 );',
		'	vReflectionFactor = mFresnelBias + mFresnelScale * pow( 1.0 + dot( normalize( I ), worldNormal ), mFresnelPower );',

		'	gl_Position = projectionMatrix * mvPosition;',

		'}'

	].join( '\n' ),

	fragmentShader: [

		'uniform samplerCube tCube;',

		'varying vec3 vReflect;',
		'varying vec3 vRefract[3];',
		'varying float vReflectionFactor;',

		'void main() {',

		'	vec4 reflectedColor = textureCube( tCube, vec3( -vReflect.x, vReflect.yz ) );',
		'	vec4 refractedColor = vec4( 1.0 );',

		'	refractedColor.r = textureCube( tCube, vec3( -vRefract[0].x, vRefract[0].yz ) ).r;',
		'	refractedColor.g = textureCube( tCube, vec3( -vRefract[1].x, vRefract[1].yz ) ).g;',
		'	refractedColor.b = textureCube( tCube, vec3( -vRefract[2].x, vRefract[2].yz ) ).b;',

		'	gl_FragColor = mix( refractedColor, reflectedColor, clamp( vReflectionFactor, 0.0, 1.0 ) );',

		'}'

	].join( '\n' )

};

export { FresnelShader };