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Tween Machine Tool

Tools / Maya Command Plugin

Tween Machine Tool

Autodesk Maya 2023

Python

PyQt

Maya's OpenMaya Python API 2.0

Plugin Development

A simplified recreation of the Tween Machine tool built as a Maya Command Plugin in Python using the OpenMaya API, paired with a custom PyQt UI. (Github)

The tool inserts a new in-between key at the current frame and shifts its value toward either the previous or next key based on a user-controlled tween slider. It works on both animated DAG objects (affecting all their animation curves) and directly selected curves.
(Note: The red tick for new keys doesn’t appear in the screen capture, but the curve view shows the key being created.)

Tool Demo
Tween with DAG
Tween with DAG
Tween with Curves
Tween with Curves
Error on no selection
Error on no selection
Tween Outputs

The Command Plugin

  • Extends MPxCommand (Maya Python API 2.0) to create an undoable tweening command.
  • Collects animation curves from either selected curves or all curves on selected animated DAG objects.
  • Throws errors if nothing is selected or no animated objects are found.
  • For each curve, checks for an existing key at the current time and updates its value based on the tween slider.
  • If no key exists, verifies the current time lies between two keys and inserts a new in-between key.
  • Computes the key value using weighted interpolation from the UI’s tween value.
  • Registers the operation with Maya’s undo system.
  • It adds the addKey operation to animation cache to ensure it's undoable.

    • The User Interface

    The UI is developed with PyQt.
    The UI script ensures that the tween machine plugin is loaded before displaying the UI. It loads the plugin if it's not already loaded or throws an error if it is unable to load the plugin.
    The UI elements are simple: a slider for selecting the tween value, a text label for the slider and another label to display the current slider value.
    The tween machine command is called when the slider value is changed and only when the slider was pressed but not released.

    Tween Machine UI