Blender Git Loki

BGE bug #17657 fixed: dRotY doesn't work properly after 90 degrees rotation.

This problem is caused by discontinuities in the conversion
orientation matrix -> euler angles: the angle sign can
switch and thus the direction of the rotation produced
by the dRot Ipo.

To avoid this bug, the matrix->euler conversion must be
avoided during the game. I took the following approach that
is compatible with Blender (identical effect in the game and
in the 3D view):

- no change in Add mode: Rot and dRot are treated as additional
rotation to the orientation at the start of the Ipo. There is
no matrix->euler conversion and thus no discontinuities.

- Rot Ipo are treated as absolute rotation. All 3 axis should
be specified but if they are not, the startup object orientation
will be used to set the unspecified axis. By doing a matrix->
euler conversion once at the start, the discontinuities are
avoided. If there are also dRot curves, they are treated as
delta of the corresponding Rot curve or startup angle.

- dRot Ipo are treated as Add mode in Local axis.

Note about Add mode: Rot and dRot curves are treated identically
during the game. However, only dRot curves make sense because
they don't interfere with the object orientation in the 3D view.