Autodesk's Maya is a 3D modeling and animation program that gives animators and modelers a variety of customizable tools to streamline or automate their work. One of these tools is the Expressions Editor which allows you to create automation scripts from within the program interface. The scripts, known as expressions, are typically used to automate animation actions to make the process of animating a rigged model go more smoothly.
Maya Scripting
- Maya allows scripting in two languages: Python and the Maya-specific Maya Embedded Language (MEL). Python is typically used to add new features and design elements to the Maya software itself, expanding the capabilities of the program as a whole. MEL, on the other hand, is generally used more as a "shortcut" language, creating scripts that perform certain actions within the software's preexisting capabilities. Some Maya features are only accessible via scripting, as they are part of the script engine itself and do not have separate entries in the program's menus or user interface.
Expressions
- Expressions in Maya are a special type of script that automates specific tasks within the program, usually scripted in MEL. Many of the tasks that expressions are created for are actions that would have to be performed multiple times, such as animating the flapping of a bird's wing. By using an expression instead of performing the task by hand, you ensure that it is performed exactly the same way every time. In some situations, you may even perform a task with a greater degree of accuracy when using expressions than you would achieve by hand.
Expression Editor
- Expressions are typically created in the Maya Expression Editor, an extension of the scripting engine that is accessible via the user interface. The Expression Editor lets you to create expressions without having to script them in an external editor. The Editor also allows you to run new expressions without having to restart Maya or install the script to a specific folder. Syntax is very important in expressions, as the scripting engine uses a strict interpretation of the scripting language, and returns errors and aborts your script if it encounters an incorrect use of syntax.
Runtime Processing
- Expression scripts are not loaded in advance in Maya, but are instead executed in real time when the script is run. The scripting engine processes the expression script one line at a time, performing any actions encountered on a line before moving on to the next line. If it comes across incorrect syntax or other errors in a script, then any actions on previous lines are still taken, but script processing stops when the error is encountered. Depending on the nature of the error, scene data may be lost as a result of the script terminating while an action was underway.
