Programming in AliceChapter 2

Today’s Agenda Designing a Program Writing Methods Executing Instructions Simultaneously Comments Tips for Setting Up an Initial Scene

2-2

Steps in Creating Programs

Four step process1. What is problem?2. Design or plan ahead3. Implement or write the program4. Test to see if it works

2-3

Scenario Problem statement or story Also called requirement specifications In Alice consists of

o World sceneo Objectso Actions

2-4

Scenario Provides Answers To What story is to be told? What objects are needed?

o Primary objectso Background objects

What actions are to take place?o Become instructions in program

2-5

Scenario: First Encounter

After traveling through space, a robot-manned craft just landed on a moon

The robot sets up a camera so scientists in Houston can view this historic event

The camera view shows the robot, lunar lander and nearby rocks

An alien surprises the robot when it peeks out from behind a rock

The robot sees the alien and walks over for a closer look

The alien is frightened and hides behind rocks The robot calls Houston to report alien

2-6

Step 1: What is Problem?

What story will be told?o A robot’s first encounter with an alien on a distant

moon What objects are used?

o Robot, lunar lander, alien, lunar background What actions take place?

o Alien peeks out from behind rocko Robot turns head around & moves toward alieno Alien hides behind rockso Robot sends message back to earth

2-7

Pseudo Code

List of English worded steps to perform a task Provides algorithmic structure Breaks problem down into smaller tasks List all things that will be done in a scene You can also make basic drawing to better

illustrate scene you wish to create Book refers to pseudo code Algorithm will be used in this class since it is

a more familiar word and has similar meaning

2-8

Example Sketch For Scenario

2-9

Scenario Scene Not intended to be artistic

o Can use simple circles, squares and lineso Label color of shapes

Just give an idea of what scene will look like

2-10

Create Initial World

Use Alice scene editor to add objects Arrange objects in various poses Capture screen as each successive

scene is created for storyboard

2-11

Algorithm for First Encounter Scenario Do following steps in order Alien moves up Alien says "Slithy toves?" Robot's head turns around Entire Robot turns to look at alien Do together Robot moves toward alien Robot legs walk Alien moves down Robot turns to look at camera Robot’s head turns red to signal danger Robot says “Houston, we have a problem!”

2-12

Step 3: Algorithm Implementation

Translate algorithm steps into program Program

o A list of instructions to have objects perform animation actions from algorithm

When programming you need to be concerned witho Syntax – statement structure and punctuation

Alice takes care of this for you You drag instruction to method editor

o Semantics – meaning of statementso Sequence – order of programming instructions

2-13

Translating the Design Some algorithm steps can be written as a

single instructiono Ex: robot turns to face alien

Other steps are composite actions that require more than one instructiono To make the robot legs walk you need more than

one instruction to cause multiple legs to move forward and bend at a joint

2-14

Writing Methods

• What is a method?o Set of instructionso Create methods by

dragging tiles from details pane into the Method Editor

o These tiles are the instructions

o Method Editor not available in Scene Editor mode

2-15

my first method

Method Editor

Dragging Method Tile to Editor • To place instruction in method editor drag from

details pane• Pop-up menu appears asking for direction, select one• Pop-up menu then asks for amount of distance to

moveo Example: move instruction

Arguments used in example Distance amount (use predefined values or other (enter value with

keyboard)) Direction

Drag method to editor

2-16

Method with Instruction Tiles

• Methods execute the instructions (tiles) that are dragged into the Method Editor

2-17

Terminology

• Calling a method - executing a method• Parameter – tells method more information on what to do• Argument – information sent to method

• For method hare.move what direction to move?• Possibilities for direction parameter are up, down, left, right• How far to move is another argument to send move method

• Passing arguments• A method is called with arguments sent to its parameters

2-18

object

argument argument

editing tagmethod name

Entering Custom Number

• When other is chosen• A number pad pops up

o Can enter number with keyboard

o Click on number pad Does not always work

o Click Okay or Cancel when done

o ‘/’ is for fractions instead of manually calculating it

2-19

Editing Tag

• Holds optional arguments• What appears depends on the method

• Ex: Duration - amount of time for action to take place• Default - 1 second

2-20

Duration Argument

Each instruction takes 1 second to execute by default

Can change time with duration option

Increase or decrease duration for realismo Increase to show movement over long distance and timeo Decrease to speed up actiono Synchronize objects together

Example: Make leg move in sync with lunar robot o Lunar robot moved 1 sec at timeo Each leg needed to move forward and backward in 1 seco Therefore move forward ½ sec and backward ½ sec

2-21

Style Argument

Specifies how smoothly one movement will blend into next movemento Gently – begins and end graduallyo Abruptly – begins and ends instantly

Sometimes needed for smooth transition since gently shows what appears to be an abrupt end and beginning

o Begin gently – begins gradually, ends instantly

o End gently – begins instantly, ends gradually

2-22

Instructions (Methods) Methods available to use are:

o Move – forward, backward, up, down, left, right In meters

o Turn – left, right, forward, backward (revolutions)o Roll – left, right (revolutions)o Resize – increase or decrease sizeo Say – put thought bubble over objecto Turn to face – select who to turn to face

2-23

Primitive Methods

All objects have common set of built-in methods for performing actions

These “primitive methods” get objects to move, turn, change size, etc

Seen in methods tab of details pane

See list in Table 2-1 (pp. 65-66) with explanation of each one

2-24

dot notation: hare.move

Control Statements Determines the sequence

instructions are executed Drag instruction to code

editor Sequential Action Block

o Actions occur one after another

Simultaneous Action Blocko Actions occur at same time

Drag block into editor

Do in order

2-25

Do in Order By default, instructions

are executed one after the other in the order they appear in the Method Editor

It is best to place instructions in “Do in order” blocko Will be easier to move

group of instructions if needed later

2-26

2-26

Do Together

• For simultaneous actions, drag“Do together” into the MethodEditor

• Place instructions to be executed simultaneously in “Do together” block

• Make sure the duration for allitems in “Do together” are same• Otherwise some will finish

quicker than others 2-27

2-27

Nesting• Sometimes two groups of

instructions need to be executed simultaneously

• Done by placing a “Do in order” block within a “Do together” block

• Example has brother penguin turn head right and left at same time as sister penguin does

• If head was turned left and right together nothing would happen• Head would turn right and left at

exact same time

2-28

Create Program Choose which sequence to execute

instructionso At same timeo Consecutively

Refer to algorithm to find instruction order

2-29

FirstEncounter Program

2-30

Demonstrate Program

Demonstrate creating FirstEncounter

2-31

Step 4: Testing Important step in creating a program is to run

ito To be sure it does what you expect it to do

Use an incremental development processo Write a few lines of code then run ito Write a few more lines and run ito Write a few more lines and run ito Allows finding many problems and fix them as you

go Called debugging – find bugs or errors in program

2-32

Comments

Make the code understandable Not all combination of instructions are

immediately obvious Explains purpose of segment of program to

human reader Helps

o You read program latero Others when determining what program does

Alice ignores comments when executing program

2-33

Comment Example

2-34

//comment tile

Comment

Tips for Setting Up Initial Scene

2-35

Can set initial position of objects in scene byo Using mouse mode

buttons from chapter 1o Right clicking object in

object tree and move mouse of methods

Moving Object to Center of World• Use move to method

and choose entire world as method’s argument

• Places object’s center point at world’s center point of (0, 0, 0)o This drives hare’s lower

body into groundo Center of gravity of hare

is in abdomen

• Useful when lose object in scene or to set starting point

2-36

Positioning Character’s Arms

2-37

Tips for Setting Up Initial Scene• Positioning objects a specified

distance apart• Ex: position teapot’s center point ½

meter to right of plate’s center pointo Move teapot object so its center point is

same as plate’s center pointo Set pointOfView in properties of both

objects world’s center point of (0, 0, 0)o Use move method by right clicking on

teapot then method then choose direction of right then ½ meter under amount

2-38

Moving Camera To An Object

• Right-click the object and choose Camera get a good look at this

• Camera moves to a position so the object is in plain view

2-39

Homework Read chapter 2 Do tutorials

o Tutorials 2-1, p 62o Tutorials 2-2, p. 67o Tutorials 2-3, p. 82o Tutorials 2-4, p. 89o Tutorials 2-5, p. 98

Answer questions in handout Do lab assignments after handing in

answered questions Due one week after assigned with 1 week

grace1-40