Alice in Action with Java Chapter 2 Methods

Objectives Build world-level methods to help organize a story into scenes and shots Build class-level methods to elicit desirable behaviors from objects Reuse a class-level method in multiple worlds Use dummies to reposition the camera for different shots within a scene Understand how an object’s position, orientation, and point of view are determined Alice in Action with Java

Methods Programs consist of a set of statements Method: behavior-producing message Objects have predefined methods for basic tasks Methods may also be created by Alice developers Two reasons for building your own methods To organize your story into more manageable pieces To provide an object with additional behaviors Alice in Action with Java

World Methods for Scenes and Shots Scene: segment of a story Shot: part of a scene from a given camera position User stories can be divided into scenes and shots A convenient technique for completing a project Divide and conquer approach to building user stories Break a big problem into smaller problems Solve each of the smaller problems Combine the smaller problems into a solution Alice in Action with Java

Methods for Scenes Scenario: develop a user story with three scenes Convention for naming methods Name should be a verb or verb phrase Name should describe what the method does Creating the first new method Select the world object Click the create new method in the details area Enter playScene1 in the New Method dialog box Check new method by sending say() to ground First test fails because my_first_method() is empty Alice in Action with Java

Methods for Scenes (continued) Alice in Action with Java

Methods for Scenes (continued) Alice in Action with Java

Methods for Scenes (continued) How to fix the first bug Click on the tab for my_first_method Drag a doInOrder control to the top of the pane Click on world in the object tree Drag playScene1() into the doInOrder statement Extend technique used to build playScene1() Add two methods: playScene2(), playScene3() New method sends a say() message to the ground New Methods are called in my_first_method() Alice in Action with Java

Methods for Scenes (continued) Alice in Action with Java

Methods for Scenes (continued) Alice in Action with Java

Methods for Shots Scenes can be divided into shots Shots can be further divided into pieces Reasons for using scenes, shots, and pieces To create a program that reflects the user story To create a program that has a modular design Example of a scheme using scenes and shots Level 1: my_first_method() Level 2: three methods for three scenes Level 3: four methods for four shots in Scene 2 Alice in Action with Java

Methods for Shots (continued) Implementing the scheme Test each shot in Scene 2 using a say() method Call the four shot methods from playScene2() Call three scene methods from my_first_method() Structure diagram reflects organization of user story All objects added to world become part of world Scene and shot messages are stored in the world World method: affects behavior of multiple objects Alice in Action with Java

Methods for Shots (continued) Alice in Action with Java

Methods for Shots (continued) Alice in Action with Java

Object Methods for Object Behaviors Object method: defines behavior for a single object Illustration: flapWings()should be sent to a dragon Comments: explanatory remark ignored by Alice Example 1: Telling a Dragon to Flap its Wings Add a dragon object to the world Select dragon from object tree and click methods tab Click create new method and enter flapWings Send roll() messages to each of the dragon’s wings Invoke flapWings() from my_first_method() Add comments to the flapWings() method Alice in Action with Java

Object Methods for Object Behaviors (continued) Alice in Action with Java

Object Methods for Object Behaviors (continued) Alice in Action with Java

Object Methods for Object Behaviors (continued) Example 2: Telling a Toy Soldier to March Four actions correspond to four steps for march() 1 marchLeft; 2 marchRight; 3 marchRight; 4 marchLeft. Define marchLeft() and marchRight() methods These methods produce reverse behaviors Incorporate new methods into march() Call march()four times from my_first_method() Alice in Action with Java

Object Methods for Object Behaviors (continued) Alice in Action with Java

Object Methods for Object Behaviors (continued) Alice in Action with Java

Alice Tip: Reusing Your Work Copy and past techniques speed up development How to use make copy to duplicate statements Right-click bar in editing area containing method Select make copy Example using make copy Refer to my_first_method() in Toy Soldier program Copy three march() statements from first march() Alice in Action with Java

Alice Tip: Reusing Your Work (continued) Alice in Action with Java

Using the Clipboard Alice clipboard Used to copy and paste all statement types Located in the events area Using Alice clipboard in Toy Soldier program Drag doInOrder in my_first_method() to clipboard Create scene1() method Drag statement in clipboard to editing area Drop statement in the scene1() method Only one statement may be placed in the clipboard You can increase the number of available clipboards Alice in Action with Java

Using the Clipboard (continued) Alice in Action with Java

Using the Clipboard (continued) Alice in Action with Java

Reusing an Object in a Different World Alice lets you reuse objects in different worlds Reusing operation involves save and import tasks How to save the dragon object Rename the dragon object flappingDragon Right-click flappingDragon, select save object… Navigate to appropriate storage location in the directory Click the Save button How to import an object into a new world Open new world and choose Import from File menu Navigate to object location and select .a2c file Alice in Action with Java

Reusing an Object in a Different World (continued) Alice in Action with Java

Reusing an Object in a Different World (continued) Alice in Action with Java

Alice Tip: Using Dummies Review Scenes comprise shots Shots are filmed with the camera in a given position Alice places a camera object in every world Two techniques for shifting position of camera Use set of motion-related messages, such as move() Use an invisible marker called a dummy Alice in Action with Java

Dummies Dummy: invisible marker with a point of view Dummies are used to change a camera’s position Description of a scene that will use dummies Wizard intervenes to prevent trolls from taking a castle Camera changes position for each of three shots Story conforms to structure in Figure 2-11 (less Shot 4) Setting up the first shot of Scene 2 Add castle, wizard, and trolls to build the scene Click more controls button and then drop a dummy Go to object tree and rename dummy scene2Shot1 Alice in Action with Java

Dummies (continued) Alice in Action with Java

Dummies (continued) Alice in Action with Java

Dummies (continued) Setting up the second shot of Scene 2 Using camera controls, zoom in on the wizard Press the drop dummy at camera button Rename the second dummy, scene2Shot2 Setting up the third shot of Scene 3 First dummy will be reused for this shot After dummies are inserted they will be programmed Alice in Action with Java

Dummies (continued) Alice in Action with Java

Using setPointOfView() to Control the Camera obj.setPointOfView(obj2) Changes the position of obj to obj2 Example: camera.setPointOfView(aDummy) Adding code to the first shot of Scene 2 Drag a doInOrder statement to the editing area Click on camera object in the object tree Drag setPointOfView()to the editing area Select scene2Shot1 dummy as target and 0 duration Add say() statements for each of the trolls Add a comment to explain the purpose of the method Alice in Action with Java

Using setPointOfView() to Control the Camera (continued) Alice in Action with Java

Using setPointOfView() to Control the Camera (continued) Alice in Action with Java

Using setPointOfView() to Control the Camera (continued) Adding code to the second shot of Scene 2 Set the opacity of the wizard to 0 in properties pane Drag wizard’s opacity property to editing area Set the opacity to 1 in the set() method Set the camera’s point of view to scene2Shot2 Add a say() statement for the wizard Adding code to the third shot of Scene 2 Reset camera’s point of view to scene2Shot1 Point the three trolls at the wizard Set message’s onlyAffectYaw attribute to true Alice in Action with Java

Using setPointOfView() to Control the Camera (continued) Alice in Action with Java

Using setPointOfView() to Control the Camera (continued) Alice in Action with Java

Thinking in 3D Learn about 3D movement to work in Alice Object’s position Determines object’s location in the 3D world Object’s orientation Determines the way an object is facing Alice in Action with Java

An Object’s Position Three axes are used to define the world space LEFT-RIGHT (LR): world’s width dimension UP-DOWN (UD): world’s height dimension FORWARD-BACKWARD (FB): world’s depth Three values specify object’s position in the world lr: point along the LR axis ud: point along the UD axis fb: point along the FB axis Change an object’s position using move() Directional values given with respect to object’s axes Alice in Action with Java

An Object’s Position (continued) Alice in Action with Java

An Object’s Position (continued) Alice in Action with Java

An Object's Orientation Combines yaw, pitch, and roll (provides direction) Yaw: amount of object’s rotation about the UD-axis Example: turn(RIGHT, 0.25) Pitch: amount of object’s rotation about the LR-axis Example: turn(FORWARD, 0.25) Roll: amount of object’s rotation about the FB-axis Example: roll(LEFT, 0.25) Alice in Action with Java

An Object's Orientation (continued) Alice in Action with Java

An Object's Orientation (continued) Alice in Action with Java

An Object's Orientation (continued) Alice in Action with Java

Point of View Combines object’s position and orientation Six values in point of view: [(lr, ud, fb),(yaw, pitch, roll)] Six values correspond to six degrees of freedom Methods used to change six values move(), turn(), and roll() Method used to change point of view setPointOfView() Alice in Action with Java

Summary Divide and conquer approach: decomposing a user story into scenes and shots Define methods to support modular design and provide advanced operations World methods: messages sent to the world Object methods: define a behavior for a single object Comments: remarks that explain program statements Alice in Action with Java

Summary (continued) Alice clipboard: stores a copy of any statement Dummy: invisible marker with position and orientation (a point of view) Object’s position: location specified using three coordinate axes Object’s orientation comprises yaw, pitch, and roll An Alice object has six degrees of freedom Alice in Action with Java