Re: [K3d-development] Strange behavior when rotating object

[Timothy M. S. <ts...@k-...>]

Giuseppe Zompatori wrote:
> Anders Dahnielson ha wrote:
> 
>>Try rotate (orient) an object around the Y axis in either positive or
>>negative direction using the spinbutton. After 90 degrees; 91 degrees Y
>>will become X 180, Y 89 and Z 180, resulting in a jump back and forth
>>between Y 89 and 90 degrees when using the spinbutton.

> Sounds like the infamous "gimbal lock".

Yup, that's what that it is.  Internally, we use an Angle-Axis 
representation of orientation for objects, see:

   http://k3d.sourceforge.net/cgi-bin/wiki?RepresentingRotations

Angle-Axis does not have a problem with gimbal lock, but we are 
converting back-and-forth to Euler angles in the UI layer, which causes 
the same problem (actually, it may exacerbate the problem).  I'd be 
interested to hear some thoughts on how other apps handle this issue - 
my assumption is that they either suffer from gimbal lock or offer 
alternate ways to specify orientation in the UI.  I have it in mind that 
we may need to offer multiple ways to pick an angle (this would be 
analogous to the multiple methods for picking a color in the Gimp).  It 
may-or-may-not be that our Euler <-> Angle-Axis conversion could be 
improved, as well.

Cheers,
Tim