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 1. What is problem? 2. Design or plan ahead 3. Implement or write the program 4. Test to see if it works 2-3

4. Scenario Problem statement or story Also called requirement specifications In Alice consists of o World scene o Objects o Actions 2-4

5. Scenario Provides Answers To What story is to be told? What objects are needed? o Primary objects o Background objects What actions are to take place? o Become instructions in program 2-5

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 2-6

7. 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 rock o Robot turns head around & moves toward alien o Alien hides behind rocks o Robot sends message back to earth 2-7

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 2-8

9. Example Sketch For Scenario 2-9

10. Scenario Scene Not intended to be artistic o Can use simple circles, squares and lines o Label color of shapes Just give an idea of what scene will look like 2-10

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 2-11

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!” 2-12

13. 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 with o Syntax – statement structure and punctuation  Alice takes care of this for you  You drag instruction to method editor o Semantics – meaning of statements o Sequence – order of programming instructions 2-13

14. Translating the Design Some algorithm steps can be written as a single instruction o Ex: robot turns to face alien Other steps are composite actions that require more than one instruction o 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

15. Writing Methods What is a method? o Set of instructions o 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

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 o 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

17. Method with Instruction Tiles Methods execute the instructions (tiles) that are dragged into the Method Editor 2-17

18. 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 editing tag method name

19. 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

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 2-20

21. Duration Argument Each instruction takes 1 second to execute by default Can change time with duration option Increase or decrease duration for realism o Increase to show movement over long distance and time o Decrease to speed up action o Synchronize objects together Example: Make leg move in sync with lunar robot o Lunar robot moved 1 sec at time o Each leg needed to move forward and backward in 1 sec o Therefore move forward ½ sec and backward ½ sec 2-21

22. Style Argument Specifies how smoothly one movement will blend into next movement o Gently – begins and end gradually o 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

23. 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 size o Say – put thought bubble over object o Turn to face – select who to turn to face 2-23

24. 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

25. Control Statements Determines the sequence instructions are executed Drag instruction to code editor Sequential Action Block o Actions occur one after another Simultaneous Action Block o Actions occur at same time Drag block into editor Do in order 2-25

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 o 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 2-28

29. Create Program Choose which sequence to execute instructions o At same time o Consecutively Refer to algorithm to find instruction order 2-29

30. FirstEncounter Program 2-30

31. Demonstrate Program Demonstrate creating FirstEncounter 2-31

32. Step 4: Testing Important step in creating a program is to run it o To be sure it does what you expect it to do Use an incremental development process o Write a few lines of code then run it o Write a few more lines and run it o Allows finding many problems and fix them as you go  Called debugging – find bugs or errors in program 2-32

33. 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 later o Others when determining what program does Alice ignores comments when executing program 2-33

34. Comment Example 2-34 // comment tile Comment

35. Tips for Setting Up Initial Scene 2-35 Can set initial position of objects in scene by o Using mouse mode buttons from chapter 1 o 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) o This drives hare’s lower body into ground o Center of gravity of hare is in abdomen Useful when lose object in scene or to set starting point 2-36

37. Positioning Character’s Arms 2-37

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 o Move teapot object so its center point is same as plate’s center point o 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

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 2-39

40. Homework Read chapter 2 Do tutorials o Tutorials 2-1, p 62 o Tutorials 2-2, p. 67 o Tutorials 2-3, p. 82 o Tutorials 2-4, p. 89 o 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 grace 1-40