Find bearing without using conditionals

[OmerHassan]

I want to calculate the angle a line makes with the positive x-axis in a clockwise direction. It's a lot like a bearing except instead of North, I want the angle it makes with positive x-axis. The image illustrates what I'm after.



Below is the code I wrote to achieve this. It works fine but I am just wondering if there's a way to reduce all these if statements.

/**
 * @return Bearing, in radians, of <code>p2</code> from <code>p1</code>
 */
public static function bearing(p1:Point, p2:Point):Number
{
    var dy:Number = p2.y - p1.y;
    var dx:Number = p2.x - p1.x;
    var theta:Number = Math.atan(dy/dx);
    
    if (theta < 0)
        if (p2.y > p1.y)
            theta += Math.PI;
        else
            theta += MathHelper._2_PI;
    else if (p2.y < p1.y)
        theta += Math.PI;
    
    return theta;
}

Edit: MathHelper._2_PI = 2 * Math.PI

[henke37]

Have you tried the atan2 function?

[OmerHassan]

atan2 looks like what I am after. Thanks, henke!