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Fix T80970: Copy Rotation constraint incorrect under shear 

Orthogonalize the constraint target's matrix before decomposing it into
Euler angles. This removes sheer, and is actually a requirement for
correct decomposition.

It's conceivable that someone has used the incorrect behaviour in a rig.
As the shear caused unpredictable flipping of the constrained object,
this is unlikely.

Reviewed By: angavrilov, sybren

Differential Revision: https://developer.blender.org/D8915
This commit is contained in:
Joseph Brandenburg 2020-11-26 13:11:23 +01:00 committed by Sybren A. Stüvel
parent 781429a8b0
commit 849debe36c
Notes: blender-bot 2023-02-14 11:28:43 +01:00 
Referenced by issue #80970, Copy Rotation constraint incorrect when target has shear
1 changed files with 8 additions and 2 deletions
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10
source/blender/blenkernel/intern/constraint.c
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@ -1833,8 +1833,14 @@ static void rotlike_evaluate(bConstraint *con, bConstraintOb *cob, ListBase *tar
/* To allow compatible rotations, must get both rotations in the order of the owner... */
mat4_to_eulO(obeul, rot_order, cob->matrix);
/* We must get compatible eulers from the beginning because
* some of them can be modified below (see bug T21875). */
mat4_to_compatible_eulO(eul, obeul, rot_order, ct->matrix);
* some of them can be modified below (see bug T21875).
* Additionally, since this constraint is based on euler rotation math, it doesn't work well with shear.
* The Y axis is chosen as the main axis when we orthoganalize the matrix because constraints are
* used most commonly on bones. */
float mat[4][4];
copy_m4_m4(mat, ct->matrix);
orthogonalize_m4_stable(mat, 1, true);
mat4_to_compatible_eulO(eul, obeul, rot_order, mat);
/* Prepare the copied euler rotation. */
bool legacy_offset = false;