Handle CHOP

From TouchDesigner 099 Wiki


The Handle CHOP is the "engine" which drives Inverse Kinematic solutions using the Handle COMP. The role of the Handle CHOP is to generate rotation values for the bones which will bring their attached handles as close to their respective targets as possible.

The use of this method is best described with an example:

  1. Increase the frame range to 10000. Create a Null COMP called 'target' and animate a few random positions for it to travel to.
  2. Create a three bone IK chain with No Kinematics. Append a Handle COMP to the last bone.
  3. In the Handle COMP set the Target menu to Target. This is the Null COMP you just created.
  4. The system is now specified. To actually start the IK enter a CHOP pane.
  5. Place a Handle CHOP. In the Source field type in the names of the bones that were earlier created.
  6. Click the Export button on the Handle CHOP and click Play. You should now see the two-bone system chasing the animated null.

Tip: In the geometry viewer, you can use the Select state to select the bones you created. Then in the Handle CHOP click the Grab Source Form Selection button. The names are entered automatically for you. You don't have to worry about being too picky when selecting objects this way, since non-bone objects are ignored.

You can place any number of bones with any number of (possibly zero) Handles attached to the system. The following parameter description will now give a more detailed explanation of the functionality:

PythonIcon.png handleCHOP_Class

Parameters - Handle Page

Source - Creates rx/ry/rz channels for each bone listed.

Fixed - If you have entered bones which form a branch or should act as a unit, enter them here. An example may be two bones splitting at the shoulders. You want them to rotate, but only as a unit.

Iterations - Increasing this parameters gives a more accurate solution at the cost of cooking time. Preroll (only when precalculating a range of frames, SingleFrame turned off): This will cook the solution a given number of frames before the requested frame range. Max Angle Change: This will limit the delta angle degrees the bones can move in any given frame. Use this to tame erratic behavior.

Init Frame /init - Specifies a frame in which the bones are reset to their default rest angles.

Preroll /preroll - Specifies the number of iterations to solve at the initialization frame.

Max Angle Change /delta - Specifies the maximum change in degrees the solver is allowed to move each bone per frame. Use this parameter if the solution is too drastic.

Grab Source From selection - Short-cut for entering bone names.

See Also

Standard Options and Local Variables