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MEL Scripting for Maya Animators

Mark R. Wilkins and Chris Kazmier

Table of Contents

• Preface

• Special Acknowledgement

• Chapter 1 – Maya Under the Hood

• In this chapter you will learn
• Why Look Under the Hood?
• The Dependency Graph, Attributes, and Connections
• Example 1: Using the Hypergraph to Explore the Dependency Graph
• Transform Hierarchy and Parent/Child Relationships
• Examining the Hierarchy
• Transform and Shape Nodes
• Example 2: Exploring Transform and Shape Nodes, Instancing, and History
• MEL and Maya's User Interface
• What to Remember about How Maya Works Behind the Scenes
  

• Chapter 2 – The Basics of MEL Commands

• In this chapter you will learn
• Can I Use MEL Without Scripting?
• Command Line and Command Feedback Line
• Command Shell
• Script Editor
• Script Editor versus Command Shell
• Script Editor's Messages as MEL Code
• Making Shelf Buttons for a MEL Script
• Saving a MEL Script
• Seductive Dangers of the Status Message Area
• The whatIs Command
• Basic Structure of MEL Commands
• Where to Find Information About Maya and MEL on the Internet
• What to Remember About How to Use MEL Without Writing Scripts
  

• Chapter 3 – Using Expressions

• In this chapter you will learn
• What Is an Expression?
• How Does an Expression Work?
• Equals Sign: Equality and Assignment
• How Maya Implements Expressions
• Is Maya's Expression Language the Same as MEL?
• When (and When Not) to Use an Expression
• Defining Relationships Between Attributes
• What Is Operator Precedence?
• Walkthrough of Maya's Expression Language
• Example 1: Eyes
• What to Remember About Using Expressions
  

• Chapter 4 – Controlling Particles with Expressions

• In this chapter you will learn
• Two Kinds of Particle Object Attributes: Per Object and Per Particle
• All About Vectors
• Two Kinds of Expressions: Ordinary and Particle
• Example 1: Ordinary Expressions and a Newton Field
• Example 2: Simple Particle Expression
• A Few Hints for Efficient Particle Expressions
• Example 3: Helical Particles Around a Curve
• What to Remember about Particle Expressions in Maya
  

• Chapter 5 – Problem Solving with MEL Scripting

• In this chapter you will learn
• MEL's Role in Maya: Building Scenes
• Strategies for Planning MEL Applications
• The Simplest User Interface
• Creating, Editing, and Querying Nodes in MEL
• Adding, Setting, and Getting Values of Attributes in MEL
• Connecting Attributes in MEL
• Creating and Connecting Expression Nodes in MEL
• Example 1: Using MEL to Automate Setup for Spiral Particles
• What to Remember About Writing MEL Scripts
  

• Chapter 6 – Variables and Data Types

• In this chapter you will learn
• Declaring Variables (and Not Declaring Them)
• Environment Variables
• MEL Statements and Type Checking
• Simple and Aggregate Data Types
• What to Remember About Variables and Data Types in MEL
  

• Chapter 7 – Using MEL Commands

• In this chapter you will learn
• What Is a MEL Command?
• Structure of a MEL Command
• Using MEL Commands in MEL Scripts
• Avoid Using MEL Commands in Expressions
• What to Remember About Using MEL Commands
  

• Chapter 8 – Manipulating Nodes in MEL

• In this chapter you will learn
• Using ls Command to Find Nodes by Name or Other Properties
• Using select Command to Manage Object Selection
• Creating Nodes in a Maya Scene
• Finding a Node's Parents and Children
• Finding Information on Node Connections
• About Maya's Node Types and the DG Node Reference
• What to Remember About Managing Nodes in MEL
  

• Chapter 9 – Controlling the Flow of Execution

• In this chapter you will learn
• Controlling the Flow of Script Execution
• Basic Conditional Operations: if-else and switch
• Loops
• What to Remember About Controlling the Flow of Execution in MEL
  

• Chapter 10 – Procedures and Functions

• In this chapter you will learn
• Top-Down Design
• Example 1: A Trip to the Grocery Store
• What are Procedures and Functions?
• Example 2: Geometry-Constrained Locators
• Example 3: Recursive Antenna
• What to Remember About Procedures, Functions, and Top-Down Design in MEL
  

• Chapter 11 – Naming Nodes, Scripts, and Variables

• In this chapter you will learn
• Why Naming Conventions Are Important
• Naming Scripts
• Naming Variables
• Naming Nodes
• Example 1: Adding a Name Prefix to Objects in a Hierarchy
• Example 2: Changing Name Prefixes in a Hierarchy
• What are Namespaces?
• Strategies for Using Namespaces
• What to Remember about Naming Scripts, Variables, and Nodes
  

• Chapter 12 – Designing MEL User Interfaces

• In this chapter you will learn
• What is a User Interface?
• What Maya Users Expect to See from a MEL Script
• Questions to Answer Before Designing a User Interface
• Designing and Testing a User Interface
• Structure of a Dialog Box
• What to Remember About Designing User Interfaces in MEL
  

• Chapter 13 – Simple MEL User Interfaces

• In this chapter you will learn
• Collecting Information from Users
• Validating User Input: When and Why
• Asking for Confirmation with confirmDialog
• Asking User for Text String with promptDialog
• Asking User to Pick File or Directory with fileDialog
• Handling Warnings and Errors with warning and error Commands
• Using Regular Expressions and match to Validate Data
• How Regular Expressions Work
• Validating Integers
• Validating Floating-Point Numbers
• Validating Object Names (Without Namespaces)
• Example 1: Simple Dialogs and Input Validation
• What to Remember about Simple MEL User Interfaces and Input Validation
  

• Chapter 14 – Custom Dialog Boxes

• In this chapter you will learn
• How to Structure a Script that Uses a Custom Dialog Box for Input
• Dialog Boxes and Their Contents
• Example 1: Making the Example Dialog Box
• Common Types of Controls
• Common Types of Layouts
• Example 2: Dialog Box for Making Geometric Primitives
• What to Remember About Building Custom Dialog Boxes in MEL
  

• Chapter 15 – Installing MEL Scripts

• In this chapter you will learn
• Installing a Script to Make It Available in All Scenes
• Installing a Script to Run When Maya Starts
• Installing a Script into a Script Node in a Scene
• Installing Custom Menus
• Managing Button Shelves and Creating Custom Shelf Icons
• What to Remember About Installing MEL Scripts
  

• Chapter 16 – Examples Using MEL with Particle Dynamics

• Example 1: Introduction to Particle Goals
• Example 2: Particle Goals in a Surface
• Example 3: Using Goals on Multiple Surfaces
• Example 4: Using Goals on Multiple Surfaces, Part 2

• Chapter 17 – Examples Using MEL with Solid Body Dynamics

• Example 1: Particle Collisions
• Example 2: Collision Events
• Example 3: Collisions Between Objects in Solid Dynamics
• Example 4: Solid Dynamics and Particles
  

• Chapter 18 – Example of a Simple Crowd System

• Example 1: Creating a Vehicle
• Example 2: Vehicle Interaction
• Example 3: Vehicle Environment
• Example 4: Fine Tuning and Completing the Script
• Full Script Reference: crowdSystem.mel
  

• Chapter 19 – Examples Using MEL in Character Rigging

• Example 1: Character Controls
• Example 2: Building a Character User Interface
• Full Text of mrBlahControls.mel
  

• Appendix A – A MEL Script Design Checklist

• Specifying the Problem
• Implementing the Main Script
• Implementing the User Interface