/**
 * Hue and saturation adjustment
 * https://github.com/evanw/glfx.js
 * hue: -1 to 1 (-1 is 180 degrees in the negative direction, 0 is no change, etc.
 * saturation: -1 to 1 (-1 is solid gray, 0 is no change, and 1 is maximum contrast)
 */

THREE.HueSaturationShader = {

	uniforms: {

		'tDiffuse': { value: null },
		'hue': { value: 0 },
		'saturation': { value: 0 }

	},

	vertexShader: [

		'varying vec2 vUv;',

		'void main() {',

		'	vUv = uv;',

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

		'}'

	].join( '\n' ),

	fragmentShader: [

		'uniform sampler2D tDiffuse;',
		'uniform float hue;',
		'uniform float saturation;',

		'varying vec2 vUv;',

		'void main() {',

		'	gl_FragColor = texture2D( tDiffuse, vUv );',

		// hue
		'	float angle = hue * 3.14159265;',
		'	float s = sin(angle), c = cos(angle);',
		'	vec3 weights = (vec3(2.0 * c, -sqrt(3.0) * s - c, sqrt(3.0) * s - c) + 1.0) / 3.0;',
		'	float len = length(gl_FragColor.rgb);',
		'	gl_FragColor.rgb = vec3(',
		'		dot(gl_FragColor.rgb, weights.xyz),',
		'		dot(gl_FragColor.rgb, weights.zxy),',
		'		dot(gl_FragColor.rgb, weights.yzx)',
		'	);',

		// saturation
		'	float average = (gl_FragColor.r + gl_FragColor.g + gl_FragColor.b) / 3.0;',
		'	if (saturation > 0.0) {',
		'		gl_FragColor.rgb += (average - gl_FragColor.rgb) * (1.0 - 1.0 / (1.001 - saturation));',
		'	} else {',
		'		gl_FragColor.rgb += (average - gl_FragColor.rgb) * (-saturation);',
		'	}',

		'}'

	].join( '\n' )

};
