Part 1 - Generating Galaxy Axis and Arms

generateArms.cs

Vector3 GetPoint()
{
    Vector3 v;
    double armDivisor = Math.PI / armCount;

    while (true)
    {
        // Generate a random normalised point with a weighting
        // towards the center controlled by the gravity variable
        v = NextV3(-1, 1).Normalized() * Math.Pow(Next(0, 1.0), gravity);

        // Some points will not conform to the parameters
        if (random.NextDouble() > conformChance)
            break;

        bool valid = false;

        // Calculate the global angle of the point around the axis
        var d = Math.Atan2(v.X, v.Z);

        // Check if this point lands on an arm
        for (double j = -Math.PI; j <= Math.PI; j += armDivisor)
        {
            // A point lands on an arm if its distance
            // from the start of the arm is less than angle * armDistance
            if (d > j && d < j + armDivisor * armSpread)
            {
                valid = true;
                break;
            }
        }

        if (valid)
            break;
    }
    
    v.Y = 0;
    return v * galaxySize;
}