#ifndef __NOISE_2D__
#define __NOISE_2D__

#include "noiseMath.cginc"

//
// Description : Array and textureless GLSL 2D simplex noise function.
//      Author : Ian McEwan, Ashima Arts.
//  Maintainer : stegu
//     Lastmod : 20110822 (ijm)
//     License : Copyright (C) 2011 Ashima Arts. All rights reserved.
//               Distributed under the MIT License. See LICENSE file.
//               https://github.com/ashima/webgl-noise
//               https://github.com/stegu/webgl-noise
// 

float snoise(float2 v)
{
	const float4 C = float4(0.211324865405187,  // (3.0-sqrt(3.0))/6.0
						    0.366025403784439,  // 0.5*(sqrt(3.0)-1.0)
						   -0.577350269189626,  // -1.0 + 2.0 * C.x
						    0.024390243902439); // 1.0 / 41.0
	// First corner
	float2 i  = floor(v + dot(v, C.yy) );
	float2 x0 = v -   i + dot(i, C.xx);

	// Other corners
	float2 i1;
	//i1.x = step( x0.y, x0.x ); // x0.x > x0.y ? 1.0 : 0.0
	//i1.y = 1.0 - i1.x;
	i1 = (x0.x > x0.y) ? float2(1.0, 0.0) : float2(0.0, 1.0);
	// x0 = x0 - 0.0 + 0.0 * C.xx ;
	// x1 = x0 - i1 + 1.0 * C.xx ;
	// x2 = x0 - 1.0 + 2.0 * C.xx ;
	float4 x12 = x0.xyxy + C.xxzz;
	x12.xy -= i1;

	// Permutations
	i = mod289(i); // Avoid truncation effects in permutation
	float3 p = permute( permute( i.y + float3(0.0, i1.y, 1.0 ))
							   + i.x + float3(0.0, i1.x, 1.0 ));

	float3 m = max(0.5 - float3(dot(x0,x0), dot(x12.xy,x12.xy), dot(x12.zw,x12.zw)), 0.0);
	m = m*m ;
	m = m*m ;

	// Gradients: 41 points uniformly over a line, mapped onto a diamond.
	// The ring size 17*17 = 289 is close to a multiple of 41 (41*7 = 287)

	float3 x = 2.0 * frac(p * C.www) - 1.0;
	float3 h = abs(x) - 0.5;
	float3 ox = floor(x + 0.5);
	float3 a0 = x - ox;

	// Normalise gradients implicitly by scaling m
	// Approximation of: m *= inversesqrt( a0*a0 + h*h );
	m *= 1.79284291400159 - 0.85373472095314 * ( a0*a0 + h*h );

	// Compute final noise value at P
	float3 g;
	g.x  = a0.x  * x0.x  + h.x  * x0.y;
	g.yz = a0.yz * x12.xz + h.yz * x12.yw;
	return 130.0 * dot(m, g);
}

#endif