[Bf-extensions-cvs] [de73210a] master: glTF importer: New attempt to fix antipodal quaternion issue

[Julien Duroure]

Commit: de73210a2ebaca137f5f9d98011e8d66899fc441
Author: Julien Duroure
Date:   Tue Feb 5 13:20:47 2019 +0100
Branches: master
https://developer.blender.org/rBAde73210a2ebaca137f5f9d98011e8d66899fc441

glTF importer: New attempt to fix antipodal quaternion issue

===================================================================

M	io_scene_gltf2/blender/imp/gltf2_blender_animation_bone.py

===================================================================

diff --git a/io_scene_gltf2/blender/imp/gltf2_blender_animation_bone.py b/io_scene_gltf2/blender/imp/gltf2_blender_animation_bone.py
index 5bf14826..65f68c4f 100755
--- a/io_scene_gltf2/blender/imp/gltf2_blender_animation_bone.py
+++ b/io_scene_gltf2/blender/imp/gltf2_blender_animation_bone.py
@@ -84,13 +84,6 @@ class BlenderBoneAnim():
     @staticmethod
     def parse_rotation_channel(gltf, node, obj, bone, channel, animation):
         """Manage rotation animation."""
-        # Note: some operations lead to issue with quaternions. Converting to matrix and then back to quaternions breaks
-        # quaternion continuity
-        # (see antipodal quaternions). Blender interpolates between two antipodal quaternions, which causes glitches in
-        # animation.
-        # Converting to euler and then back to quaternion is a dirty fix preventing this issue in animation, until a
-        # better solution is found
-        # This fix is skipped when parent matrix is identity
         blender_path = "pose.bones[" + json.dumps(bone.name) + "].rotation_quaternion"
         group_name = bone.name
 
@@ -107,12 +100,6 @@ class BlenderBoneAnim():
         else:
             quat_keyframes = [quaternion_gltf_to_blender(vals) for vals in values]
 
-        # Manage antipodal quaternions
-        # (but is not suffisant, we also convert quaternion --> euler --> quaternion)
-        for i in range(1, len(quat_keyframes)):
-            if quat_keyframes[i].dot(quat_keyframes[i-1]) < 0:
-                quat_keyframes[i] = -quat_keyframes[i]
-
 
         if not node.parent:
             final_rots = [
@@ -129,15 +116,20 @@ class BlenderBoneAnim():
                 final_rots = [
                     bind_rotation.rotation_difference(
                         (parent_mat @ quat_keyframe.to_matrix().to_4x4()).to_quaternion()
-                    ).to_euler().to_quaternion()
+                    )
                     for quat_keyframe in quat_keyframes
                 ]
             else:
                 final_rots = [
-                    bind_rotation.rotation_difference(quat_keyframe).to_euler().to_quaternion()
+                    bind_rotation.rotation_difference(quat_keyframe)
                     for quat_keyframe in quat_keyframes
                 ]
 
+        # Manage antipodal quaternions
+        for i in range(1, len(final_rots)):
+            if final_rots[i].dot(final_rots[i-1]) < 0:
+                final_rots[i] = -final_rots[i]
+
         BlenderBoneAnim.fill_fcurves(
             obj.animation_data.action,
             keys,