I've come to a point in my game where I need to calculate an angle depending on the X,Y values of the mouse relative to a given point. The first thing I did was try to reverse engineer the CalculateVector() function found in V2SpaceShooter.kpl. Didn't work. =/ Next I tried using Math.ArcCos for the X value and Math.ArcSin for the Y value. I get a few intelligible numbers when the mouse is close to ( 1-2 pixels away from ) the screen edge. Anywhere else and I get a cryptic "NaN" value. Huh? What does "NaN" mean? And why do ArcCos and ArcSin return it as a number?

 Mostly though, how do I use ArcCos or ArcSin to calculate an angle of a line ( or Vector ) that stretches from point A to point B, assuming that I will get 0 if B.x = A.x and B.y < a.Y (In other words, a line that goes from 0,0 to 0,10 will give me an angle of 180, and a line from 0,10 to 0,0 gives the angle of 0)?
 

PS. If that was hard to understand, I can try to think up a few more examples.

In a hurry;   try ArcTan( y / x )  or ArcTan( x / y ). May be you have to add 180 or 270.

Think I have more time for that on sunday.

Michael

The easy parts first:

NaN = "Not a Number"

ArcCos means "the angle (in radians) whose cosine is". And since cosines of angles can only have values from -1 to +1, if you try to do

ArcCos(2.5) = NaN (since it is out of range)
 

MichaelH:

try ArcTan( y / x )  or ArcTan( x / y ). May be you have to add 180 or 270.

Thanks! Using ArcTan instead of ArcCos or ArcSin, I was able to create a function that will calculate the angle of a vector.

    Function AngleFromVector( X As Decimal, Y As Decimal ) As Decimal
       
        Var Result As Decimal
       
        // First, check what angle measurement unit we are currently using, and remember it
        Var MathAngleUnit As Int =  math.AngleMeasureUnit
       
        // Now, set the angle measurement to degrees
        Math.AngleMeasureUnit = Degrees
       
        // Calculate the angle
        If Y > 0 Then
            Result = (ArcTan( X*-1 / Y ))
        Else If Y < 1 Then
            Result = (ArcTan( X*-1 / Y ) - 180)
        End If
       
        // Lastly, restore the math angle measurement to the previous value
        Math.AngleMeasureUnit = MathAngleUnit
       
        Return result
    End Function

Again, Thanks!