A first attempt at implementing forward and inverse kinematics.
Contents I. Directions II. Features III. Implementation IV. Sources
I. Directions Run with: bin/main static/skeletonN.skel Press the space bar to switch between forward and inverse kinematics mode. Press left or right to rotate the skeleton.
i. Forward Kinematics
Hold the mouse down on the bone you want to manipulate, then drag the mouse
up or down. The joint will rotate along its axis.
ii. Inverse Kinematicsk
Click on a bone to add or remove a constrant for it. Use the mouse to drag
and drop the constrant. Right click and drag up or down on the constraint
to move it in or out of the screen.
II. Features This system only supports rotational joints, and allows specification of an arbitrary skeleton in the .skel format, detailed below. The mouse only interface allows for easy visual manipulation of the skeleton.
skel format: Your skeleton must be a rooted tree, where each joint is a node, and the .skel format represents a preorder traversel of that tree. For each joint, you must specify in order: length, rotation axis, initial angle, and the number of direct children it has. Check out the examples.
III. Implementation The skeleton data structure is a tree of joints, each with a rotational axis and angle.
i. Forward Kinematics
I use the OpenGL matrix stack to traverse the skeleton tree and draw joints
in their appropriate locations.
ii. Inverse Kinematics
The IK interface uses glm to project the mouse position to coordinates in
the world with a specified depth. It provides tools to make matrix
calculations easy. The IK minimization algorithm is done using Eigen's
NonLinearOptimization module. The Jacobian is calculated by performing a
first order Taylor approximation.
IV. Sources My use of Eigen draws heavily from the provided examples. I discussed with a friend from home how to write the mouseToObj function for the IK interface, so that was a joint effort. Besides this, old StackOverflow questions and similar sites provided a lot of debugging help.