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Fix glitch in SpringBoneSimulator3D by storing the previous frame's rotation instead of using no rotation when the axis is flipped #101651

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merged 1 commit into from
Jan 17, 2025
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Fix glitch in SpringBoneSimulator3D by storing the previous frame's rotation instead of using no rotation when the axis is flipped #101651

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16 changes: 12 additions & 4 deletions scene/3d/spring_bone_simulator_3d.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1498,6 +1498,7 @@ void SpringBoneSimulator3D::_init_joints(Skeleton3D *p_skeleton, SpringBone3DSet
setting->joints[i]->verlet->prev_tail = setting->joints[i]->verlet->current_tail;
setting->joints[i]->verlet->forward_vector = axis.normalized();
setting->joints[i]->verlet->length = axis.length();
setting->joints[i]->verlet->prev_rot = Quaternion(0, 0, 0, 1);
} else if (setting->extend_end_bone && setting->end_bone_length > 0) {
Vector3 axis = get_end_bone_axis(setting->end_bone, setting->end_bone_direction);
if (axis.is_zero_approx()) {
Expand All @@ -1508,6 +1509,7 @@ void SpringBoneSimulator3D::_init_joints(Skeleton3D *p_skeleton, SpringBone3DSet
setting->joints[i]->verlet->length = setting->end_bone_length;
setting->joints[i]->verlet->current_tail = setting->cached_center.xform(p_skeleton->get_bone_global_pose(setting->joints[i]->bone).xform(axis * setting->end_bone_length));
setting->joints[i]->verlet->prev_tail = setting->joints[i]->verlet->current_tail;
setting->joints[i]->verlet->prev_rot = Quaternion(0, 0, 0, 1);
}
}
setting->simulation_dirty = false;
Expand Down Expand Up @@ -1570,10 +1572,13 @@ void SpringBoneSimulator3D::_process_joints(double p_delta, Skeleton3D *p_skelet
verlet->prev_tail = verlet->current_tail;
verlet->current_tail = next_tail;

// Apply rotation.
// Convert position to rotation.
Vector3 from = current_rot.xform(verlet->forward_vector);
Vector3 to = p_inverted_center_transform.basis.xform(next_tail - current_origin).normalized();
Quaternion from_to = get_from_to_rotation(from, to);
Quaternion from_to = get_from_to_rotation(from, to, verlet->prev_rot);
verlet->prev_rot = from_to;

// Apply rotation.
from_to *= current_rot;
from_to = get_local_pose_rotation(p_skeleton, p_joints[i]->bone, from_to);
p_skeleton->set_bone_pose_rotation(p_joints[i]->bone, from_to);
Expand All @@ -1588,10 +1593,13 @@ Quaternion SpringBoneSimulator3D::get_local_pose_rotation(Skeleton3D *p_skeleton
return p_skeleton->get_bone_global_pose(parent).basis.orthonormalized().inverse() * p_global_pose_rotation;
}

Quaternion SpringBoneSimulator3D::get_from_to_rotation(const Vector3 &p_from, const Vector3 &p_to) {
Quaternion SpringBoneSimulator3D::get_from_to_rotation(const Vector3 &p_from, const Vector3 &p_to, const Quaternion &p_prev_rot) {
if (Math::is_equal_approx((float)p_from.dot(p_to), -1.0f)) {
return p_prev_rot; // For preventing to glitch, checking dot for detecting flip is more accurate than checking cross.
}
Vector3 axis = p_from.cross(p_to);
if (axis.is_zero_approx()) {
return Quaternion(0, 0, 0, 1);
return p_prev_rot;
}
float angle = p_from.angle_to(p_to);
if (Math::is_zero_approx(angle)) {
Expand Down
3 changes: 2 additions & 1 deletion scene/3d/spring_bone_simulator_3d.h
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Original file line number Diff line number Diff line change
Expand Up @@ -72,6 +72,7 @@ class SpringBoneSimulator3D : public SkeletonModifier3D {
Vector3 prev_tail;
Vector3 current_tail;
Vector3 forward_vector;
Quaternion prev_rot;
float length = 0.0;
};

Expand Down Expand Up @@ -266,7 +267,7 @@ class SpringBoneSimulator3D : public SkeletonModifier3D {

// Helper.
static Quaternion get_local_pose_rotation(Skeleton3D *p_skeleton, int p_bone, const Quaternion &p_global_pose_rotation);
static Quaternion get_from_to_rotation(const Vector3 &p_from, const Vector3 &p_to);
static Quaternion get_from_to_rotation(const Vector3 &p_from, const Vector3 &p_to, const Quaternion &p_prev_rot);
static Vector3 snap_position_to_plane(const Transform3D &p_rest, RotationAxis p_axis, const Vector3 &p_position);
static Vector3 limit_length(const Vector3 &p_origin, const Vector3 &p_destination, float p_length);

Expand Down