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:
- Increase the frame range to 10000. Create a Null COMP called 'target' and animate a few random positions for it to travel to.
- Create a three bone IK chain with No Kinematics. Append a Handle COMP to the last bone.
- In the Handle COMP set the Target menu to Target. This is the Null COMP you just created.
- The system is now specified. To actually start the IK enter a CHOP pane.
- Place a Handle CHOP. In the Source field type in the names of the bones that were earlier created.
- 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:
Parameters - Handle Page
source - Creates
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 - Specifies a frame in which the bones are reset to their default rest angles.
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.
Parameters - Common Page
timeslice - Turning this on forces the channels to be "Time Sliced". A Time Slice is the time between the last cook frame and the current cook frame.
scope - To determine which channels get affected, some CHOPs use a Scope string on the Common page.
Sample Rate Match
srselect - ⊞ - Handle cases where multiple input CHOPs' sample rates are different. When Resampling occurs, the curves are interpolated according to the Interpolation Method Option, or "Linear" if the Interpolate Options are not available.
- Resample At First Input's Rate
first- Use rate of first input to resample others.
- Resample At Maximum Rate
max- Resample to the highest sample rate.
- Resample At Minimum Rate
min- Resample to the lowest sample rate.
- Error If Rates Differ
err- Doesn't accept conflicting sample rates.
exportmethod - ⊞ - This will determine how to connect the CHOP channel to the parameter. Refer to the Export article for more information.
- DAT Table by Index
datindex- Uses the docked DAT table and references the channel via the index of the channel in the CHOP.
- DAT Table by Name
datname- Uses the docked DAT table and references the channel via the name of the channel in the CHOP.
- Channel Name is Path:Parameter
autoname- The channel is the full destination of where to export to, such has
autoexportroot - This path points to the root node where all of the paths that exporting by Channel Name is Path:Parameter are relative to.
exporttable - The DAT used to hold the export information when using the DAT Table Export Methods (See above).
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Exporting is the connection of CHOP channels to parameters of operators. The output of each exporting CHOP is one or more channels, active only while the CHOP Viewer is on. The current value of a channel can be exported to a parameter of any operator, overriding that parameter's value. See Parameter.
The term "Frame" is used (1) in the Timeline, (2) as a time-unit in CHOPs, (3) as a time-unit in TOPs, and (4) with movies images which are read and created with TOPs.
A Time Slice is the time from the last cook frame to the current cook frame. In CHOPs it is the set of short channels that only contain the CHOP channels' samples between the last and the current cook frame.
A parameter in most CHOPs that restricts which channels of that CHOP will be affected. Normally all channels of a CHOP are affected by the operator.
samples-per-second of a CHOP. Each CHOP in your network has a sample rate, whether it is used or not. The overall timeline has a "frame rate", which is the number of animation frames per second, generally your monitor display frequency.
Parameters in TouchDesigner are an operator's settings (numbers, menus, flags, strings, paths) which the user can alter. Parameters for any operator can be opened by right-clicking on the operator and selecting "Parameters..." A currently selected operator's parameters can be viewed in a Network Editor by pressing the keyboard shortcut 'p'.