[Bf-python] BPython bug AngleBetweenVecs

[Jonathan Merritt]

Campbell Barton wrote:

> Hi, this has caused me grief in the past and I have been using a
> python version of AngleBetweenVecs.
>
> Just now I found the problem. when AngleBetweenVecs compares 2 vectors
> that are the same, it can return  nan, nan being a float type.
> nothing is equal to nan except float('nan').
> Shold be changed to return 0 instead of nan?\


I just took a quick look, and I'd say this method needs a bit of a
re-write.  In addition to the bug you mention, it also has the
additional (undocumented bug/feature) side-effect of normalizing any
vectors that are passed to it.

if you try:
    v1 = Mathutils.Vector(1,2,3)
    v2 = Mathutils.Vector(1,2,3)
    print Mathutils.AngleBetweenVecs(v1,v2)
you get a small number (close to zero), as expected.

if you then try:
    v1 = Mathutils.Vector(1,2,3)
    print Mathutils.AngleBetweenVecs(v1,v1)
you get nan.

Within the function, the vectors should be copied *first* before they
are normalized (so that you don't have any side-effects).  It will then
work better (giving you the first result and not a NAN).  Can't write a
patch just now, but can do it next weekend if nobody gets there before me.

-- 
Jonathan Merritt BE(Mech)/BSc
PhD Student - Equine Biomechanics
The University of Melbourne
Veterinary Clinical Centre, Werribee