book

MEL Scripting for Maya Animators, 2nd Edition

by Mark R. Wilkins, Chris Kazmier

August 2005

Intermediate to advanced

552 pages

11h 58m

English

Morgan Kaufmann

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Dedication
AcknowledgmentsSpecial Acknowledgment
In this chapter you will learnWhy Look Under the Hood?The Dependency Graph, Attributes, and ConnectionsExample 1: Using the Hypergraph to Explore the Dependency GraphTransform Hierarchy and Parent/Child RelationshipsExamining the HierarchyTransform and Shape NodesExample 2: Exploring Transform and Shape Nodes, Instancing, and HistoryMEL and Maya’s User InterfaceWhat to Remember About How Maya Works Behind the Scenes
In this chapter you will learnCan I Use MEL Without Scripting?Command Line and Command Feedback LineCommand ShellScript EditorScript Editor Versus Command ShellScript Editor’s Messages as MEL CodeMaking a Shelf Button for a MEL ScriptSaving a MEL ScriptSeductive Dangers of the Status Message AreaThe whatIs CommandBasic Structure of MEL CommandsWhere to Find Information About Maya and MEL on the InternetWeb SitesNewsgroupsHow to Use MEL Scripts Found on the InternetWhat to Remember About How to Use MEL Without Writing Scripts
In this chapter you will learnWhat Is an Expression?How Does an Expression Work?Equals Sign: Equality and AssignmentHow Maya Implements ExpressionsIs Maya’s Expression Language the Same as MEL?When (and When Not) to Use an ExpressionDefining Relationships Between AttributesWhat Is Operator Precedence?Walkthrough of Maya’s Expression LanguageDefinitions of VariablesComputing the Values of AttributesAssigning Computed ValuesExample 1: EyesAnalyzing the ProblemPlanning the Eyes’ Animation ControlsWriting the ExpressionWhat to Remember About Using Expressions
In this chapter you will learnTwo Kinds of Particle Object Attributes: Per Object and Per ParticleAll About VectorsCreating a Vector VariableManipulating Vector ComponentsAdding and Subtracting VectorsOther Useful Vector OperationsunitmaganglecrossdotrotTwo Kinds of Expressions: Ordinary and ParticleUsing Ordinary Expressions to Control Particle BehaviorExample 1: Ordinary Expressions and a Newton FieldHow this expression worksWhen to Use a Particle ExpressionExample 2: A Simple Particle ExpressionHow This Expression WorksA Few Hints for Efficient Particle ExpressionsExample 3: Helical Particles Around a CurveBrainstorming Possible SolutionsA First Attempt at the Particle ExpressionHow this expression worksRefining the SolutionWhat to Remember About Particle Expressions in Maya
In this chapter you will learnMEL’s Role in Maya: Building ScenesStrategies for Planning MEL ApplicationsThe Simplest User InterfaceCreating, Editing, and Querying Nodes in MELAdding, Setting, and Getting Values of Attributes in MELConnecting Attributes in MELCreating and Connecting Expression Nodes in MELExample 1: Using MEL to Automate Setup for Spiral ParticlesHow It WorksWhat to Remember About Writing MEL Scripts

In this chapter you will learnDeclaring Variables (and Not Declaring Them)Local and Global VariablesGlobal Variables, Attributes, and Option VariablesEnvironment VariablesMEL Statements and Type CheckingSimple and Aggregate Data TypesIntegersDefinitionHow to declare an integer variableInteger arithmetic operationsCombining arithmetic and assignmentsFloating-Point NumbersDefinitionHow to declare an integer variableUseful floating-point operationsCautionary note about floating-point comparisonsConversions Between Integers and Floating-Point NumbersVectorsDefinitionHow to declare a vector variableWorking with vectorsOther common vector operationsStringsDefinitionHow to declare a string variableArraysDefinitionHow to declare an arrayWorking with array contentsArray size property and its implicationsChoosing Between Arrays and VectorsWhat to Remember About Variables and Data Types in MEL
In this chapter you will learnWhat Is a MEL Command?Where to Find the MEL Command You NeedAsk an experienced MEL programmerRead related scripts from the Internet or elsewhereRead the documentationStructure of a MEL CommandQuery, Create, and Edit ModesOther Command FlagsCommand ArgumentsUsing MEL Commands in MEL ScriptsUsing MEL Commands as StatementsUsing BackticksUsing evalAvoid Using MEL Commands in ExpressionsWhat to Remember About Using MEL Commands
In this chapter you will learnUsing ls Command to Find Nodes by Name or Other PropertiesFinding Objects with a Particular Name or Partial NameGetting Names of Selected ObjectsGetting One or More Objects’ TypesFinding Objects of a Particular TypeFinding List of Objects Under a Certain Node in Transform HierarchyListing Full Path NamesUsing Select Command to Manage Object SelectionClearing the SelectionSelecting a List of ObjectsAdding to an Existing SelectionRemoving Objects from an Existing SelectionSelecting All Nodes in a SceneCreating Nodes in a Maya SceneUsing Commands Specific to a Node TypeUsing Utility Commands that Support the -ch on FlagUsing the createNode CommandFinding a Node’s Parents and ChildrenFinding Information on Node ConnectionsUsing listConnectionsUsing connectionInfoUsing isConnectedAbout Maya’s Node Types and the Node and Attribute ReferenceWhat to Remember About Managing Nodes in MEL
In this chapter you will learnControlling the Flow of Script ExecutionBasic Conditional Operations: if-else and switchIf-else StatementsConditional TestsThe not operatorThe and operatorThe or operatorSwitch StatementsLoopsWhile LoopsFor-in LoopsFor LoopsWhat to Remember About Controlling the Flow of Execution in MEL
In this chapter you will learnTop-Down DesignExample 1: A Trip to the Grocery StoreWhat Are Procedures and Functions?Scope and Global ProceduresDefining and Using Procedures and FunctionsExample 2: Geometry-Constrained LocatorsRecursionExample 3: Recursive AntennaWhat to Remember About Procedures, Functions, and Top-Down Design in MEL
In this chapter you will learnWhy Naming Conventions Are ImportantNaming ScriptsScript, Procedure, and Function NamesIdentify Data and PurposeIdentifying the Script Developer in the Script NameNaming VariablesValid and Invalid NamesIdentify Data Type and PurposeGlobal Variables: Identifying DeveloperNaming NodesValid NamesTransform PathsIdentify Type and PurposeUnique Names and Writing ScriptsExample 1: Adding a Name Prefix to Objects in a HierarchyHow the Script WorksExample 2: Changing Name Prefixes in a HierarchyHow the Script WorksWhat Are Namespaces?Finding Information About NamespacesCreating, Setting, and Deleting NamespacesStrategies for Using NamespacesWhat to Remember About Naming Scripts, Variables, and Nodes
In this chapter you will learnWhat Is a User Interface?What Maya Users Expect to See from a MEL ScriptApproach 1: Operate on the SelectionApproach 2: Using a Dialog BoxApproach 3: The Persistent Dialog BoxApproach 4: Something ElseQuestions to Answer Before Designing a User InterfaceDesigning and Testing a User InterfaceHints for Planning a Good User InterfaceDo the repetition for the userOne input window is better than manyPut effort into most-used interfacesShow choices rather than ask questionsMinimize number of choices presented to the userBuild simple tools rather than large systemsStructure of a Dialog BoxWhat to Remember About Designing User Interfaces in MEL
In this chapter you will learnCollecting Information from UsersValidating User Input: When and WhyAsking for Confirmation with confirmDialogAsking User for Text String with promptDialogAsking User to Pick File or Directory with fileDialogHandling Warnings and Errors with Warning and Error CommandsUsing Regular Expressions and match to Validate DataHow Regular Expressions WorkValidating IntegersValidating Floating-Point NumbersValidating Object Names (Without Namespaces)Example 1: Simple Dialogs and Input ValidationHow It WorksWhat to Remember About Simple MEL User Interfaces and Input Validation
In this chapter you will learnHow to Structure a Script That Uses a Custom Dialog Box for InputDialog Boxes and Their ContentsLayoutsGroupsCollectionsControlsExample 1: Making the Example Dialog BoxHow It WorksCommon Types of ControlsbuttoncheckBoxfloatFieldGrpfloatSliderGrpintFieldGrpintSliderGrptextFieldButtonGrptextFieldGrpradioButtonGrpCommon Types of LayoutscolumnLayoutformLayoutframeLayoutrowColumnLayoutrowLayoutExample 2: Dialog Box for Making Geometric PrimitivesCreating the Main ScriptBuilding the Dialog BoxDefining the Button Action ProcedureWhat to Remember About Building Custom Dialog Boxes in MEL
In this chapter you will learnWhy Use formLayout?Planning a Dialog Box for formLayoutUsing formLayout: OverviewHow It WorksUsing formLayout: Defining Placement Rules for UI Objects-attachForm-attachOppositeForm-attachControl-attachOppositeControl-attachPosition-attachNoneExample: Implementing a Dialog Box with formLayoutHow It WorksWhat to Remember About Making Dialog Boxes with formLayout
In this chapter you will learnWhat You Need to Know Before You ProceedWhat Are Web Panels?Learning Web AuthoringHow a Dialog Box Built with Web Panels WorksPlanning a Dialog Box for Web PanelsCreating a Web-Based Dialog Box for MayaLaunching a Web-Based Dialog Box from MELHow It WorksExample 1: Implementing a Dialog Box using JavaScriptHow It WorksIdeas for Dialog Boxes Built with Web PanelsWhat to Remember about Making Dialog Boxes with Web Panels
In this chapter you will learnWhat Is a Utility Node?When Should You Consider Using a Utility Node?Use utility nodes in custom shading networksUse utility nodes in place of expressions when many expressions will need to be evaluated in the sceneHow to Create and Connect a Utility NodeExample 1: Using the plusMinusAverage Node to Find the Midpoint Between Two LocatorsCommon Utility NodesplusMinusAveragemultiplyDividevectorProductconditionsetRangeWhat to Remember About Improving Performance With Utility Nodes
In this chapter you will learnInstalling a Script to Make It Available in All ScenesInstalling a Script to Run When Maya StartsInstalling a Script into a Script Node in a SceneInstalling Custom MenusManaging Button Shelves and Creating Custom Shelf IconsWhat to Remember About Installing MEL Scripts
Example 1: Introduction to Particle GoalsAdding Color and RadiusAdding VelocityExample 2: Particle Goals on a SurfacePer Particle ArraysInitial StatesExpressions and the Expression EditorWatching Values of ParticlesUsing a Lifespan Per ParticleChanging U and V with Math FunctionsExample 3: Using Goals on Multiple SurfacesExample 2 Sin Function RevisitedAdding a Custom AttributeExtraExample 4: Using Goals on Surfaces, Part 2OverviewLoad the SceneAdd Particle BallAdding Goals for Particle and Planes Using String VariablesAdding Creation Expressions to Particle BallAdd Runtime Expression
Example 1: Particle CollisionsCreate the SceneCollide the ParticlesSetting Controls for CollisionsUsing Other Controls in geoConnector NodeFinish Scene Using MELExample 2: Collision EventsOverviewAdd Emitter and ParticlesDynamic RelationshipsLimit Number of Particles and Add GravityAdd Other CollisionsEventsExpression for BucketsEdit Settings to Fix ProblemsSpeedExample 3: Collisions Between Objects in Solid DynamicsWrite Small Duplicate and Position ScriptCommon Mistakes in Assembling String VariablesCreate Collision BoxFlip Normals on collisionBoxActive and Passive Rigid BodiesMake Each Grid a Passive Collision ObjectTurn on Collision Data OptionsChange Color of Grids with CollisionsExample 4: Solid Dynamics and ParticlesCreate Interface Window for Aim Control Using MELAdd New Window Control to ShelfConvert Panel to Polygons and Break Up into PiecesAdd Dynamics and Expressions to PiecesCreate Full MEL ScriptLoad in Scene and Run ScriptPass a Float into panelBreakup
Example 1: Creating a VehicleMake Vehicle a Solid Dynamic ObjectChanging the Vehicle’s DirectionChange Motion of vehicle_1 with ExpressionCreate Wander MotionOrient vehicle_1’s Direction with Its MotionExample 2: Vehicle InteractionCreate Script to Automate Creating Vehicle in Example 1Add Radial Field to vehicle_1 to Repel Other VehiclesAdd Another VehicleAdd Simple MEL InterfaceSave and Source ScriptCreate Wrapper Script and Place on ShelfExample 3: Vehicle EnvironmentLaunch crowdSystem.melAdd Boundary ObstaclesCreate More ObstaclesConvert New Obstacles into Passive Rigid BodiesAdd collectObstacles to crowdSystem.melCreate Global ForcesCreate Matrix Variable to Use for PlacementCreate Control Slider InterfaceAdd Global Forces Procedure to crowdSystem.melExample 4: Fine Tuning and Completing the ScriptAdd New Features to User InterfaceAdd Checkbox OptionsAdd Cancel ButtonWindow StandardsAdd More VehiclesAdd Integer Pass from One Procedure to AnotherConnect Radials for Both Leaders and Followers Together with “Nested” LoopsAdd Global Forces Function to Main ScriptTest Global Forces OptionAdd Main Launch ProcedureAdd collectObstacles to ScriptAdd Objects to Scene and Run ScriptFull Script Reference: crowdSystem.mel
Example 1: Character ControlsLoad SceneOverview of SceneOverview of mrBlah’s ControlsLocking AttributesArm ControlsSet Up mrBlah’s Backbone ControlsCreate Sway Effect When Picking Up FeetExample 2: Building a Character User InterfaceLoad Saved mrBlah SceneOrganize Controls for UsersCreate mrBlahControls.melCreate Sliders to Control spinCtrl AttributesCreate Layout for Window ControlsTest WindowDisplay Only What You Want User to SeeCreate Script Node for WindowCreate Shelf Icon to Reopen Window When ClosedFull Text of mrBlahControls.mel

Content preview from MEL Scripting for Maya Animators, 2nd Edition

About the Authors

Mark R. Wilkins is a technical director at DreamWorks Animation SKG, where he helped develop a production pipeline using Maya for effects and character animation. Mark also provides training and technical assistance to animators using Maya. He previously worked at Walt Disney Feature Animation in a variety of positions including software engineer and scene setup supervisor. He has contributed to a number of films, including Dinosaur, Mission: Impossible 2, Minority Report, and Madagascar. Mark holds a degree in physics from Harvey Mudd College.

Chris Kazmier is a senior technical director at Sony Pictures Imageworks, where he creates computer-generated effects for live-action films. He has worked on projects ranging from The Haunted ...