[Bf-committers] Math gurus; euler question!

[Ton Roosendaal]

Hi,

An old annoyance in Blender, and again in bug tracker, is related to  
inserting rotation keys for objects. Objects store euler angles, but  
the transform code internally uses quaternions/matrices. This means  
that the endresult euler coming from transform (extracted from a  
matrix) can differ a lot from the old euler value, causing weird  
flipping animations when you insert that.

With my simple knowledge, I made this function long ago, in  
src/editobject.c

void compatible_eul(float *eul, float *oldrot)

	oldrot = the original rotation of the object (or key) before transform
	eul = the euler result during a transform

The code tries to correct the "eul" value to be as close to the  
original as possible. This happens not very scientific... you can see  
in the code a 'return' added, that's a part of the code that didn't  
work.

As illustration;
1) In top view, rotate the standard cube 90 degrees clockwise.
2) Open Nkey panel
3) In right-view, rotate. At 90 degrees you can see a flip in euler  
values

Question; does a textbook/standard trick exist to solve this? Without  
changing the entire transform, but just with this as input;

- old euler value
- 3x3 new rotation matrix, or euler extracted from it.

I can also be based on a recode of the arithb.c Mat3ToEul(), for  
example by giving this a third argument "reference euler" or so.

-Ton-

------------------------------------------------------------------------ 
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Ton Roosendaal  Blender Foundation ton at blender.org  
http://www.blender.org