1. Programming in Alice
Chapter 2

2. Today’s Agenda Designing a Program Writing Methods
Executing Instructions Simultaneously
Comments
Tips for Setting Up an Initial Scene
2-2

3. Steps in Creating Programs
Four step process
What is problem?
Design or plan ahead
Implement or write the program
Test to see if it works

4. Scenario Problem statement or story
Also called requirement specifications
In Alice consists of
World scene
Objects
Actions

5. Scenario Provides Answers To
What story is to be told?
What objects are needed?
Primary objects
Background objects
What actions are to take place?
Become instructions in program

6. 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

7. Step 1: What is Problem? What story will be told?
A robot’s first encounter with an alien on a distant moon
What objects are used?
Robot, lunar lander, alien, lunar background
What actions take place?
Alien peeks out from behind rock
Robot turns head around & moves toward alien
Alien hides behind rocks
Robot sends message back to earth

8. 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

9. Example Sketch For Scenario

10. Scenario Scene Not intended to be artistic
Can use simple circles, squares and lines
Label color of shapes
Just give an idea of what scene will look like

11. 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
Active Learning: Students create initial world. Illustrate use of quad view to position objects relative to one another.

12. 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!”

13. Step 3: Algorithm Implementation
Translate algorithm steps into program
Program
A list of instructions to have objects perform animation actions from algorithm
When programming you need to be concerned with
Syntax – statement structure and punctuation
Alice takes care of this for you
You drag instruction to method editor
Semantics – meaning of statements
Sequence – order of programming instructions

14. Translating the Design
Some algorithm steps can be written as a single instruction
Ex: robot turns to face alien
Other steps are composite actions that require more than one instruction
To make the robot legs walk you need more than one instruction to cause multiple legs to move forward and bend at a joint

15. Writing Methods What is a method? Method Editor Set of instructions
Create methods by dragging tiles from details pane into the Method Editor
These tiles are the instructions
Method Editor not available in Scene Editor mode
my first method
Method Editor

16. 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 move
Example: move instruction
Arguments used in example
Distance amount (use predefined values or other (enter value with keyboard))
Direction
Drag method to editor

17. Method with Instruction Tiles
Methods execute the instructions (tiles) that are dragged into the Method Editor

18. Terminology argument argument object method name editing tag
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
argument
argument
object
method name
editing tag

19. Entering Custom Number
When other is chosen
A number pad pops up
Can enter number with keyboard
Click on number pad
Does not always work
Click Okay or Cancel when done
‘/’ is for fractions instead of manually calculating it

20. Editing Tag Holds optional arguments
What appears depends on the method
Ex: Duration - amount of time for action to take place
Default - 1 second

21. Duration Argument
Each instruction takes 1 second to execute by default
Can change time with duration option
Increase or decrease duration for realism
Increase to show movement over long distance and time
Decrease to speed up action
Synchronize objects together
Example: Make leg move in sync with lunar robot
Lunar robot moved 1 sec at time
Each leg needed to move forward and backward in 1 sec
Therefore move forward ½ sec and backward ½ sec

22. Style Argument
Specifies how smoothly one movement will blend into next movement
Gently – begins and end gradually
Abruptly – begins and ends instantly
Sometimes needed for smooth transition since gently shows what appears to be an abrupt end and beginning
Begin gently – begins gradually, ends instantly
End gently – begins instantly, ends gradually

23. Instructions (Methods)
Methods available to use are:
Move – forward, backward, up, down, left, right
In meters
Turn – left, right, forward, backward (revolutions)
Roll – left, right (revolutions)
Resize – increase or decrease size
Say – put thought bubble over object
Turn to face – select who to turn to face

24. dot notation: hare.move
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 ) with explanation of each one
dot notation: hare.move

25. Control Statements Determines the sequence instructions are executed
Drag instruction to code editor
Sequential Action Block
Actions occur one after another
Simultaneous Action Block
Actions occur at same time
Drag block into editor
Do in order

26. 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” block
Will be easier to move group of instructions if needed later
2-26

27. Do Together
For simultaneous actions, drag “Do together” into the Method Editor
Place instructions to be executed simultaneously in “Do together” block
Make sure the duration for all items in “Do together” are same
Otherwise some will finish quicker than others
2-27

28. 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

29. Create Program Choose which sequence to execute instructions
At same time
Consecutively
Refer to algorithm to find instruction order

30. FirstEncounter Program
Traditional Lecture: Create the example world, line by line
Active Learning: Create a part of the example world and allow students to complete the program.

31. Demonstrate Program Demonstrate creating FirstEncounter
Traditional: Add comments as desired
Active Learning: Add a comment and have students add another

32. Step 4: Testing Important step in creating a program is to run it
To be sure it does what you expect it to do
Use an incremental development process
Write a few lines of code then run it
Write a few more lines and run it
Allows finding many problems and fix them as you go
Called debugging – find bugs or errors in program

33. Comments Make the code understandable
Not all combination of instructions are immediately obvious
Explains purpose of segment of program to human reader
Helps
You read program later
Others when determining what program does
Alice ignores comments when executing program

34. Comment Example
Comment
//comment tile

35. Tips for Setting Up Initial Scene
Can set initial position of objects in scene by
Using mouse mode buttons from chapter 1
Right clicking object in object tree and move mouse of methods

36. 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)
This drives hare’s lower body into ground
Center of gravity of hare is in abdomen
Useful when lose object in scene or to set starting point 36

37. Positioning Character’s Arms

38. 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 point
Move teapot object so its center point is same as plate’s center point
Set pointOfView in properties of both objects world’s center point of (0, 0, 0)
Use move method by right clicking on teapot then method then choose direction of right then ½ meter under amount 38

39. 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 39

40. Homework Read chapter 2 Do tutorials
Tutorials 2-1, p 62
Tutorials 2-2, p. 67
Tutorials 2-3, p. 82
Tutorials 2-4, p. 89
Tutorials 2-5, p. 98
Do lab assignments Due one week after it is assigned