[Bf-python] AngleBetweenVecs still buggy.

[Campbell Barton]

Hi Joseph, thanks for committing Theeths patch,
 From recent testing AngleBetweenVecs only returns NAN when given a zero 
length vector.
Useually Id say that it could raise an exception, but faces with a very 
small area can return there normal as (0,0,0) - so maybe it would be 
good to check if either vector is 0,0,0 and return 0 as the result. - 
Its probably not worth be writing a patch for this.

- Cam


> This would be a nice issue to be submitted to the bug tracker. Please 
> describe the conditions under which your getting NAN returned.
>
> Campbell Barton wrote:
>
>> 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
>>
>> _______________________________________________
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>
>


-- 
Campbell J Barton

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