csci 1111 - seas.gwu.edurhyspj/fall2011cs1111/lecture2.pdf · 14 methods for scenes (continued) how...

CSCI 1111Introduction to Software Development

Rhys Price Jones

Week 2Methods

based on Joel Adams

Friday, September 2, 2011

2

WEEK 2 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


3

METHODS

Method: behavior-producing message

Objects have predefined methods for basic tasks

Methods may also be created by Alice developers


4

OBJECT METHODS - EXAMPLE

Add a pterodactyl to the world

local-gallery > animals > pterodactyl

click to placethen move to desired position

use methods to set size, position, etc.

Look at the available methods

This pterodactyl cannot flap its wings


MISSING A CRUCIAL OBJECT METHOD!

Object method: defines behavior for a single object

Illustration: we would like to send flapWings() to a pterodactyl


TELLING PTERODACTYL TO FLAP WINGS

Select pterodactyl from object tree and click methods tab

Click create new method and enter flapWings

Send roll() messages to each of the dragon’s wingsInvoke flapWings() from my_first_method()

Add comments to the flapWings() method


7

Book does dragon -- not pterodactyl


8

Adding comments


TWO REASONS FOR BUILDING METHODS

To provide an object with additional behaviors: Object methods

To organize your story into more manageable pieces: World methods


10

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


11

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


12

Methods for Scenes (continued)


13



14

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()


15



16



17

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


18

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


19

Methods for Shots (continued)


20

Methods for Shots (continued)


OPEN ALICE

open world week2/WorldMethods

add a scene 4

where the ground thinks this is all pretty dull!


TWO REASONS FOR BUILDING METHODS

To provide an object with additional behaviors: Object methods

To organize your story into more manageable pieces: World methods

Back to Object Methods


23

OBJECT METHODS EXAMPLE 2

Telling a Toy Soldier to March

Four actions correspond to four steps for march()•1 marchLeft;

•2 marchRight;

•3 marchRight;

•4 marchLeft.

Better names might be halfLeftStephalfRightStep


DEFINE

marchLeft() and marchRight() methods

These methods produce reverse behaviors

Incorporate new methods into march()Call march()four times from my_first_method()


25

The marchLeft() method


26

The march() method


27

ALICE TIP: REUSING YOUR WORK

Copy and paste 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()


28

Alice Tip: Reusing Your Work (continued)


29

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


30

Using the Clipboard (continued)


31

Using the Clipboard (continued)


REUSING AN OBJECT

in a Different World

Alice lets you reuse objects in different worlds

Reusing operation involves save and import tasks


SAVE THE PTERODACTYL OBJECT

Rename the pterodactyl object flappingPterodactyl

Right-click flappingPterodactyl, select save object…

Navigate to appropriate storage location

Click the Save button

saves as FlappingPterodactyl.a2c

note capitalization


HOW TO IMPORT AN OBJECT

into a new world

Open new world and choose Import from File menu

Navigate to appropriate location and select the correct .a2c file


35

Book’s dragon example


36

Book’s dragon example


QUIZLET

1. True or False: A method name should usually be a verb or verb phrase.

Answer:

2. A method that affects the behavior of multiple objects (like a scene) should be defined as a(n) ____________________ method.

Answer:

3. A(n) ____________________ method is used to define a complex behavior for a single object.

Answer:

4. True or False: Comments are ignored by Alice.

Answer:


QUIZLET ANSWERS

1. True or False: A method name should usually be a verb or verb phrase.

Answer: True

2. A method that affects the behavior of multiple objects (like a scene) should be defined as a(n) ____________________ method.

Answer: world

3. A(n) ____________________ method is used to define a complex behavior for a single object.

Answer: object

4. True or False: Comments are ignored by Alice.

Answer: True


39

ALICE TIP: USING DUMMIES

Review

Scenes comprise shots

Shots are filmed with the camera in a given positionAlice 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 dummyDummy: 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 shotsStory 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


43

Dummies (continued)


44

Dummies (continued)


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


THIRD SHOT OF SCENE 3

First dummy will be reused for this shot


47

Dummies (continued)


48

USING SETPOINTOFVIEW()

to Control the Camera• obj.setPointOfView(obj2)

Changes the position of obj to obj2

Example: camera.setPointOfView(aDummy)


CODE FOR

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


50

Scene2Shot1


51

Scene2Shot1


CODE FOR

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


53

Scene2Shot2


CODE FOR

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


55

Scene2Shot3


56

THINKING IN 3D

Learn about 3D movement to work in Alice

Object’s position

Determines object’s location in the 3D worldObject’s orientation

Determines the way an object is facing


57

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


58

An Object’s Position (continued)


59

An Object’s Position (continued)


60

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)


61

An Object's Orientation (continued)

(pictures are better in the book!)


62



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64

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()


65

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


66

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


QUIZLET

1. From the editing area, you can drag any statement onto the ____________________ and Alice will store a copy of it there for you.

Answer:

2. A(n) ____________________ is an invisible marker in your world that has a position and an orientation.

Answer:

3. An object’s orientation is its combined ____________________, pitch, and roll.

Answer:

4. True or False: Alice objects have six degrees of freedom.


QUIZLET ANSWERS

1. From the editing area, you can drag any statement onto the ____________________ and Alice will store a copy of it there for you.

Answer: clipboard

2. A(n) ____________________ is an invisible marker in your world that has a position and an orientation.

Answer: dummy

3. An object’s orientation is its combined ____________________, pitch, and roll.

Answer: yaw

4. True or False: Alice objects have six degrees of freedom.

Answer: True


DISCUSSION

1. How does decomposing a user story into scenes and shots help you organize the components of an Alice program? 2. What is the difference between a world method and an object method? 3. What is the value of adding comments to a program? 4. How does the use of dummy markers simplify the process of changing the camera object's point of view? 5. What is meant by the assertion that an Alice object has six degrees of freedom?


csci 1111 - seas.gwu.edurhyspj/fall2011cs1111/lecture2.pdf · 14 methods for scenes (continued) how...

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