Fixes the SkeletonIK twisting issue by using the skeleton global pose without overrides

doc/classes/Skeleton.xml

@@ -80,6 +80,15 @@
 				Returns the overall transform of the specified bone, with respect to the skeleton. Being relative to the skeleton frame, this is not the actual "global" transform of the bone.
 			</description>
 		</method>
+		<method name="get_bone_global_pose_no_override" qualifiers="const">
+			<return type="Transform">
+			</return>
+			<argument index="0" name="bone_idx" type="int">
+			</argument>
+			<description>
+				Returns the overall transform of the specified bone, with respect to the skeleton, but without any global pose overrides. Being relative to the skeleton frame, this is not the actual "global" transform of the bone.
+			</description>
+		</method>
 		<method name="get_bone_name" qualifiers="const">
 			<return type="String">
 			</return>

scene/3d/skeleton.cpp

@@ -236,9 +236,6 @@ void Skeleton::_notification(int p_what) {
 			for (int i = 0; i < len; i++) {
 				Bone &b = bonesptr[order[i]];
 
-				if (b.global_pose_override_amount >= 0.999) {
-					b.pose_global = b.global_pose_override;
-				} else {
 				if (b.disable_rest) {
 					if (b.enabled) {
 						Transform pose = b.pose;
@@ -247,17 +244,20 @@ void Skeleton::_notification(int p_what) {
 						}
 						if (b.parent >= 0) {
 							b.pose_global = bonesptr[b.parent].pose_global * pose;
+							b.pose_global_no_override = bonesptr[b.parent].pose_global_no_override * pose;
 						} else {
 							b.pose_global = pose;
+							b.pose_global_no_override = pose;
 						}
 					} else {
 						if (b.parent >= 0) {
 							b.pose_global = bonesptr[b.parent].pose_global;
+							b.pose_global_no_override = bonesptr[b.parent].pose_global_no_override;
 						} else {
 							b.pose_global = Transform();
+							b.pose_global_no_override = Transform();
 						}
 					}
-
 				} else {
 					if (b.enabled) {
 						Transform pose = b.pose;
@@ -266,14 +266,18 @@ void Skeleton::_notification(int p_what) {
 						}
 						if (b.parent >= 0) {
 							b.pose_global = bonesptr[b.parent].pose_global * (b.rest * pose);
+							b.pose_global_no_override = bonesptr[b.parent].pose_global_no_override * (b.rest * pose);
 						} else {
 							b.pose_global = b.rest * pose;
+							b.pose_global_no_override = b.rest * pose;
 						}
 					} else {
 						if (b.parent >= 0) {
 							b.pose_global = bonesptr[b.parent].pose_global * b.rest;
+							b.pose_global_no_override = bonesptr[b.parent].pose_global_no_override * b.rest;
 						} else {
 							b.pose_global = b.rest;
+							b.pose_global_no_override = b.rest;
 						}
 					}
 				}
@@ -281,7 +285,6 @@ void Skeleton::_notification(int p_what) {
 				if (b.global_pose_override_amount >= CMP_EPSILON) {
 					b.pose_global = b.pose_global.interpolate_with(b.global_pose_override, b.global_pose_override_amount);
 				}
-				}
 
 				if (b.global_pose_override_reset) {
 					b.global_pose_override_amount = 0.0;
@@ -382,6 +385,13 @@ Transform Skeleton::get_bone_global_pose(int p_bone) const {
 	return bones[p_bone].pose_global;
 }
 
+Transform Skeleton::get_bone_global_pose_no_override(int p_bone) const {
+	ERR_FAIL_INDEX_V(p_bone, bones.size(), Transform());
+	if (dirty)
+		const_cast<Skeleton *>(this)->notification(NOTIFICATION_UPDATE_SKELETON);
+	return bones[p_bone].pose_global_no_override;
+}
+
 // skeleton creation api
 void Skeleton::add_bone(const String &p_name) {
 	ERR_FAIL_COND(p_name == "" || p_name.find(":") != -1 || p_name.find("/") != -1);
@@ -848,6 +858,7 @@ void Skeleton::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("clear_bones_global_pose_override"), &Skeleton::clear_bones_global_pose_override);
 	ClassDB::bind_method(D_METHOD("set_bone_global_pose_override", "bone_idx", "pose", "amount", "persistent"), &Skeleton::set_bone_global_pose_override, DEFVAL(false));
 	ClassDB::bind_method(D_METHOD("get_bone_global_pose", "bone_idx"), &Skeleton::get_bone_global_pose);
+	ClassDB::bind_method(D_METHOD("get_bone_global_pose_no_override", "bone_idx"), &Skeleton::get_bone_global_pose_no_override);
 
 	ClassDB::bind_method(D_METHOD("get_bone_custom_pose", "bone_idx"), &Skeleton::get_bone_custom_pose);
 	ClassDB::bind_method(D_METHOD("set_bone_custom_pose", "bone_idx", "custom_pose"), &Skeleton::set_bone_custom_pose);

scene/3d/skeleton.h

@@ -88,6 +88,7 @@ private:
 
 		Transform pose;
 		Transform pose_global;
+		Transform pose_global_no_override;
 
 		bool custom_pose_enable;
 		Transform custom_pose;
@@ -174,6 +175,7 @@ public:
 	void set_bone_rest(int p_bone, const Transform &p_rest);
 	Transform get_bone_rest(int p_bone) const;
 	Transform get_bone_global_pose(int p_bone) const;
+	Transform get_bone_global_pose_no_override(int p_bone) const;
 
 	void clear_bones_global_pose_override();
 	void set_bone_global_pose_override(int p_bone, const Transform &p_pose, float p_amount, bool p_persistent = false);

scene/animation/skeleton_ik.cpp

@@ -246,7 +246,7 @@ void FabrikInverseKinematic::make_goal(Task *p_task, const Transform &p_inverse_
 		p_task->end_effectors.write[0].goal_transform = p_inverse_transf * p_task->goal_global_transform;
 	} else {
 		// End effector in local transform
-		const Transform end_effector_pose(p_task->skeleton->get_bone_global_pose(p_task->end_effectors[0].tip_bone));
+		const Transform end_effector_pose(p_task->skeleton->get_bone_global_pose_no_override(p_task->end_effectors[0].tip_bone));
 
 		// Update the end_effector (local transform) by blending with current pose
 		p_task->end_effectors.write[0].goal_transform = end_effector_pose.interpolate_with(p_inverse_transf * p_task->goal_global_transform, blending_delta);
@@ -270,18 +270,7 @@ void FabrikInverseKinematic::solve(Task *p_task, real_t blending_delta, bool ove
 		return; // Skip solving
 	}
 
-	p_task->skeleton->set_bone_global_pose_override(p_task->chain.chain_root.bone, Transform(), 0.0, true);
+	// Update the initial root transform so its synced with any animation changes
-
-	if (p_task->chain.middle_chain_item) {
-		p_task->skeleton->set_bone_global_pose_override(p_task->chain.middle_chain_item->bone, Transform(), 0.0, true);
-	}
-
-	for (int i = 0; i < p_task->chain.tips.size(); i += 1) {
-		p_task->skeleton->set_bone_global_pose_override(p_task->chain.tips[i].chain_item->bone, Transform(), 0.0, true);
-	}
-
-	// Update the initial root transform
-	// (Needed to sync IK with animation)
 	_update_chain(p_task->skeleton, &p_task->chain.chain_root);
 
 	make_goal(p_task, p_task->skeleton->get_global_transform().affine_inverse(), blending_delta);
@@ -298,31 +287,6 @@ void FabrikInverseKinematic::solve(Task *p_task, real_t blending_delta, bool ove
 		Transform new_bone_pose(ci->initial_transform);
 		new_bone_pose.origin = ci->current_pos;
 
-		// The root bone needs to be rotated differently so it isn't frozen in place
-		if (ci == &p_task->chain.chain_root && !ci->children.empty()) {
-			new_bone_pose = new_bone_pose.looking_at(ci->children[0].current_pos, Vector3(0, 1, 0));
-			const Vector3 bone_rest_dir = p_task->skeleton->get_bone_rest(ci->children[0].bone).origin.normalized().abs();
-			const Vector3 bone_rest_dir_abs = bone_rest_dir.abs();
-			if (bone_rest_dir_abs.x > bone_rest_dir_abs.y && bone_rest_dir_abs.x > bone_rest_dir_abs.z) {
-				if (bone_rest_dir.x < 0) {
-					new_bone_pose.basis.rotate_local(Vector3(0, 1, 0), -Math_PI / 2.0f);
-				} else {
-					new_bone_pose.basis.rotate_local(Vector3(0, 1, 0), Math_PI / 2.0f);
-				}
-			} else if (bone_rest_dir_abs.y > bone_rest_dir_abs.x && bone_rest_dir_abs.y > bone_rest_dir_abs.z) {
-				if (bone_rest_dir.y < 0) {
-					new_bone_pose.basis.rotate_local(Vector3(1, 0, 0), Math_PI / 2.0f);
-				} else {
-					new_bone_pose.basis.rotate_local(Vector3(1, 0, 0), -Math_PI / 2.0f);
-				}
-			} else {
-				if (bone_rest_dir.z < 0) {
-					// Do nothing!
-				} else {
-					new_bone_pose.basis.rotate_local(Vector3(0, 0, 1), Math_PI);
-				}
-			}
-		} else {
 		if (!ci->children.empty()) {
 			/// Rotate basis
 			const Vector3 initial_ori((ci->children[0].initial_transform.origin - ci->initial_transform.origin).normalized());
@@ -335,13 +299,11 @@ void FabrikInverseKinematic::solve(Task *p_task, real_t blending_delta, bool ove
 
 		} else {
 			// Set target orientation to tip
-				if (override_tip_basis) {
+			if (override_tip_basis)
 				new_bone_pose.basis = p_task->chain.tips[0].end_effector->goal_transform.basis;
-				} else {
+			else
 				new_bone_pose.basis = new_bone_pose.basis * p_task->chain.tips[0].end_effector->goal_transform.basis;
 		}
-			}
-		}
 
 		// IK should not affect scale, so undo any scaling
 		new_bone_pose.basis.orthonormalize();
@@ -362,7 +324,7 @@ void FabrikInverseKinematic::_update_chain(const Skeleton *p_sk, ChainItem *p_ch
 		return;
 	}
 
-	p_chain_item->initial_transform = p_sk->get_bone_global_pose(p_chain_item->bone);
+	p_chain_item->initial_transform = p_sk->get_bone_global_pose_no_override(p_chain_item->bone);
 	p_chain_item->current_pos = p_chain_item->initial_transform.origin;
 
 	ChainItem *items = p_chain_item->children.ptrw();