class SGL_Perlin
{//http://freespace.virgin.net/hugo.elias/models/m_perlin.htm
private:
	float Linear_Interpolate(float a, float b, float x)
	{
		return  a*(1.0f-x) + b*x;
	}

	float Cosine_Interpolate(float a, float b, float x)
	{
		float ft = x * 3.1415927f;
		float f = (1.0f - cosf(ft)) * 0.5f;
		return  a*(1.0f-f) + b*f;
	}

public:
	float persistence;
	int Number_Of_Octaves;

	float SGL_Noise2D(float x, float y)
	{
		int n = (int)x + (int)y * 57;
		n = (n<<13) ^ n;
		return ( 1.0f - ( (n * (n * n * 15731 + 789221) + 1376312589) & 0x7fffffff) / 1073741824.0f);    
	}

	float SGL_SmoothNoise_2D(float x, float y)
	{
		float corners = ( SGL_Noise2D(x-1, y-1)+SGL_Noise2D(x+1, y-1)+SGL_Noise2D(x-1, y+1)+SGL_Noise2D(x+1, y+1) ) / 16.0f;
		float sides   = ( SGL_Noise2D(x-1, y)  +SGL_Noise2D(x+1, y)  +SGL_Noise2D(x, y-1)  +SGL_Noise2D(x, y+1) ) /  8.0f;
		float center  =  SGL_Noise2D(x, y) / 4.0f;
		return corners + sides + center;
	}

	float SGL_InterpolatedNoise_2D(float x, float y)
	{
		int integer_X    = int(x);
		float fractional_X = x - integer_X;

		int integer_Y    = int(y);
		float fractional_Y = y - integer_Y;

		float v1 = SGL_SmoothNoise_2D((float)integer_X,     (float)integer_Y);
		float v2 = SGL_SmoothNoise_2D((float)integer_X + 1, (float)integer_Y);
		float v3 = SGL_SmoothNoise_2D((float)integer_X,     (float)integer_Y + 1);
		float v4 = SGL_SmoothNoise_2D((float)integer_X + 1, (float)integer_Y + 1);

		float i1 = Cosine_Interpolate(v1 , v2 , fractional_X);
		float i2 = Cosine_Interpolate(v3 , v4 , fractional_X);

		return Cosine_Interpolate(i1 , i2 , fractional_Y);
	}


	float PerlinNoise_2D(float x, float y)
	{
		float total = 0;
		float p = persistence;
		int n = Number_Of_Octaves - 1;

		for(int i = 0; i<=n;i++)
		{
			float frequency = 2.0f*(float)i;// powf(2.0f,(float)i);
			float amplitude = p*(float)i;//powf(p,(float)i);
			total = total + SGL_InterpolatedNoise_2D(x * frequency, y * frequency) * amplitude;
		}
		return total;
	}
};