There is a bug in there !

Hello there,
and thanks for the help with your code ... but ultimately no thank you ... you are not going
to be pleased by my message today ... few years ago I stumbled upon your code and decided
to use it ... it worked great (if you correct the if (fabs(vz) < 1.0e-3) (not efficient enough) by if (vz == 0.0) eh , it worked ... and then a bug ... a case in a million ?

So you can check if for your self here are the data:

// The two points in space:
DRAW_CYLINDER_BOND:: PICKED:: a.x= -3.324548, a.y= -1.470013, a.z= -0.218306
DRAW_CYLINDER_BOND:: PICKED:: b.x= -2.474335, b.y= -2.652915, b.z= -0.218291
// The vector
DRAW_CYLINDER_BOND:: PICKED:: cx= 0.850213, cy= -1.182903, cz=0.000015
// The parameters of the rotation
DRAW_CYLINDER_BOND:: PICKED:: ax= 89.999404, rx= 0.000018, ry= 0.000013

As you can see it the parameters fit none of the tests in your code ...
And the result it produces (I am drawing the half bond in blue):


The only option is to use this kind of code:

https://gist.github.com/mfalda/11182888

Best a regards and thank you anyway, it was helpful.

S.