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SkeletonModification2DFABRIK

Inherits: SkeletonModification2D < Resource < RefCounted < Object

A modification that uses FABRIK to manipulate a series of Bone2D nodes to reach a target.

Description

This SkeletonModification2D uses an algorithm called Forward And Backward Reaching Inverse Kinematics, or FABRIK, to rotate a bone chain so that it reaches a target.

FABRIK works by knowing the positions and lengths of a series of bones, typically called a “bone chain”. It first starts by running a forward pass, which places the final bone at the target’s position. Then all other bones are moved towards the tip bone, so they stay at the defined bone length away. Then a backwards pass is performed, where the root/first bone in the FABRIK chain is placed back at the origin. Then all other bones are moved so they stay at the defined bone length away. This positions the bone chain so that it reaches the target when possible, but all of the bones stay the correct length away from each other.

Because of how FABRIK works, it often gives more natural results than those seen in SkeletonModification2DCCDIK. FABRIK also supports angle constraints, which are fully taken into account when solving.

Note: The FABRIK modifier has fabrik_joints, which are the data objects that hold the data for each joint in the FABRIK chain. This is different from Bone2D nodes! FABRIK joints hold the data needed for each Bone2D in the bone chain used by FABRIK.

To help control how the FABRIK joints move, a magnet vector can be passed, which can nudge the bones in a certain direction prior to solving, giving a level of control over the final result.

Properties

Methods

Property Descriptions

int fabrik_data_chain_length = 0

• void set_fabrik_data_chain_length ( int value )

• int get_fabrik_data_chain_length ( )

The number of FABRIK joints in the FABRIK modification.

NodePath target_nodepath = NodePath("")

• void set_target_node ( NodePath value )

• NodePath get_target_node ( )

The NodePath to the node that is the target for the FABRIK modification. This node is what the FABRIK chain will attempt to rotate the bone chain to.

Method Descriptions

NodePath get_fabrik_joint_bone2d_node ( int joint_idx ) const

Returns the Bone2D node assigned to the FABRIK joint at joint_idx.

int get_fabrik_joint_bone_index ( int joint_idx ) const

Returns the index of the Bone2D node assigned to the FABRIK joint at joint_idx.

Vector2 get_fabrik_joint_magnet_position ( int joint_idx ) const

Returns the magnet position vector for the joint at joint_idx.

bool get_fabrik_joint_use_target_rotation ( int joint_idx ) const

Returns whether the joint is using the target’s rotation rather than allowing FABRIK to rotate the joint. This option only applies to the tip/final joint in the chain.

void set_fabrik_joint_bone2d_node ( int joint_idx, NodePath bone2d_nodepath )

Sets the Bone2D node assigned to the FABRIK joint at joint_idx.

void set_fabrik_joint_bone_index ( int joint_idx, int bone_idx )

Sets the bone index, bone_idx, of the FABRIK joint at joint_idx. When possible, this will also update the bone2d_node of the FABRIK joint based on data provided by the linked skeleton.

void set_fabrik_joint_magnet_position ( int joint_idx, Vector2 magnet_position )

Sets the magnet position vector for the joint at joint_idx.

void set_fabrik_joint_use_target_rotation ( int joint_idx, bool use_target_rotation )

Sets whether the joint at joint_idx will use the target node’s rotation rather than letting FABRIK rotate the node.

Note: This option only works for the tip/final joint in the chain. For all other nodes, this option will be ignored.