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double findnoise2(double x, double y)
{
    int n = (int)x+(int)y*57;
    n = (n<<13)^n;
    int nn = (n*(n*n*60493+19990303)+1376312589)&0x7fffffff;
    return 1.0-((double)nn/1073741824.0);
}

double interpolate(double a, double b, double x)
{
    double ft = x * 3.1415927;
    double f = (1.0-cos(ft))* 0.5;
    return a*(1.0-f)+b*f;
}

double noise(double x, double y)
{
	double floorx = (double)((int)x);
	double floory = (double)((int)y);
	double s,t,u,v;
	s = findnoise2(floorx, floory);
	t = findnoise2(floorx+1, floory);
	u = findnoise2(floorx, floory+1);
	v = findnoise2(floorx+1, floory+1);
	double int1 = interpolate(s, t, x-floorx);
	double int2 = interpolate(u, v, x-floorx);
	return interpolate(int1, int2, y-floory);
}

GLuint renderCloud(int w, int h, double zoom, double p)
{
    int octaves = 2;
    GLuint tex = 0;
    glGenTextures(1, &tex);
    glBindTexture(GL_TEXTURE_2D, tex);
    unsigned char *pixels = (unsigned char *)malloc(w*h*sizeof(unsigned char));
	for(int y=0; y<h; y++)
	{
        for(int x=0; x<w; x++)
        {
            double getnoise = 0;
            for(int a=0; a<octaves-1; a++)
            {
                double frequency = pow(2, a);
                double amplitude = pow(p, a);
                getnoise += noise(((double)x)*frequency/zoom, ((double)y)/zoom*frequency)*amplitude;
            }
            int color = (int)((getnoise*128.0)+128.0);
            if(color>255)
                color = 255;
            if(color<0)
                color = 0;
            pixels[(h*y)+x] = color;
        }
	}

    glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, w, h, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, pixels);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    return tex;
}