Motion at an Angle 2D (For the Games FAQ)

[Milk]

There is an ArcTangent function. To avoid losing sign I use this

Option Explicit
Public Const PI As Double = 3.14159265358979
Public Const PI½ As Double = 1.5707963267949

Public Function ATan2(ByVal Dy As Double, ByVal Dx As Double) As Double
  If Dx = 0 Then
    ATan2 = PI½ * Sgn(Dy)
  Else
    ATan2 = Atn(Dy / Dx)
    If Dx < 0 Then ATan2 = ATan2 + PI
  End If
End Function

Works fine as Single too in most cases