[Bf-python] AngleBetweenVecs still buggy.

[Campbell Barton]

Hi, There are a number of existing fixes for Mathutils.AngleBetweenVecs 
being buggy. For the Nth time I'm  using a python workaround, but its 
frustrating that there have been 4 people who have released fixes, some 
~5 months old.

Heres what I'm currently using as a python wrapper that works around 
Anglebetween Vecs returning NAN.


# VEC ANGLE NEVER RETURNS NAN!
#=============================================================================#
# Math functions   
#=============================================================================#
X,Y,Z = 0,1,2

def vecMagnitude(vec):
    '''Calculates the magnitude of a vector and returns the result.

         Assumes the vector is an XYZ vector.
    '''
    return math.sqrt(vec[X]**2 + vec[Y]**2 + vec[Z]**2)


def vecDotProduct(vec1, vec2):
    """Calculates the dot product of two vectors and returns it.

         Assumes all the vectors are XYZ vectors.
    """
    return vec1[X]*vec2[X] + vec1[Y]*vec2[Y] + vec1[Z]*vec2[Z]


def vecAngle(vec1, vec2):
    """Calculates the angle between two vectors (in degrees) and returns it.

         Assumes all the vectors are XYZ vectors.
    """
    # Assume they could be the same first.
    if vec1.x == vec2.x and\
    vec1.y == vec2.y and\
    vec1.z == vec2.z:
        return 0
   
   
    # Try NAN returning mathutils first
    ang = Mathutils.AngleBetweenVecs(vec1, vec2)
    if ang == ang: # Not nan?
        return ang
   
    # Ick Blender cant do it se we have to.
   
    denom = vecMagnitude(vec1) * vecMagnitude(vec2)
    if denom != 0:
        quotient = vecDotProduct(vec1, vec2) / denom

        #clip the quotient to acceptable values for acos
        if quotient > 1:
            quotient = 1
        if quotient < -1:
            quotient = -1

        return math.acos(quotient) / math.pi * 180.0
    else:
        #the vectors are perpendicular
        return 90.0