Alice: Functions

1. Alice: Functions Alice Chapter 6 September 19, 2005

2. Checkpoint • 80 point quiz • Abstract article - quick summary (What cool thing did you read about?) • Turn in to Ms. K • Demos of methods & parameters animation • Today I am going to have you follow along in Alice as I am presenting the material • Make a world with two toyballs (Sports) in it (one large, one small)

3. Writing your own functions • Functions do not change the state of the world • Instead, they return a value • Sometimes there are no built-in functions that do what you want to do • One example: Let’s say you want to simulate a ball rolling forward • It’s more difficult than it seems!

4. Rolling Ball • Try: Ball.turn(forward, 1 revolution) • The ball simply rotates in place • Maybe try to move the ball forward at the same time that it turns forward • Try: Write a class-level method, realisticRoll: doTogether{ ball.move (forward, 1 meter) ball.turn(forward, 1 revolution) } • The ball still ends up in the same place

5. Rolling Ball • The ball is moving relative to itself, but we want it to move relative to the ground, so let’s change our class-level method to: doTogether{ ball.move (forward, 1 meter, asSeenBy ground) ball.turn(forward, 1 revolution) } • This just guesses that 1 revolution looks right, but what happens if we have a large ball and a small ball rolling forward?

6. Rolling Ball • The distance covered in one revolution of the ball is proportional to the diameter • If we wanted the ball to roll for 10 meters, how many revolutions would a large ball need to make? How about a small ball? • We want a way to calculate this, depending on the ball’s diameter • We need a new function

7. Create a new function • Try: Create new function • Call it numberOfRevolutions and select Number for the return type • You will see a new editor panel for your function with a Return <None> line at the bottom

8. Returning a value • Every function must have a Return statement • In our problem, we are asking the function: “How many revolutions does the ball have to make to move a given distance along the ground?” • This depends on the distance traveled by the circumference of the ball in a single revolution numRevolutions = distance / (diameter * pi)

9. Writing out function • To calculate numRevolutions = distance / (diameter * pi) we need to know: • Distance (a parameter sent in to the function) • Diameter (the width of the ball - a built-in function) • Pi (a constant value, we will approximate it to 3.14) • We can use the built-in functions and mathematical operators to put this equation into the return part of this function

10. Another new function • Let’s build a fly-space, with a biplane (Vehicle) and a helicopter (Vehicle) flying at approximately the same altitude near the airport (Buildings) • Let’s build a function that checks for possible collisions when two vehicles are in the same fly-space • If they are TooClose, the flight controller can radio the planes to change their flight paths

11. isTooClose • Need to know: aircraft1, aircraft2, minimumAllowedDistance • We will return a Boolean (true/false) answer • Here we need an if/else control structure • Check if absolute value of aircraft1.distanceAbove(aircraft2) < minimumAllowedDistance if so, return true, else return false

12. avoidCollision • Then the world.avoidCollision method could be called if the airplanes were too close • Would need to check which airplane was above the other • If airplane1 above, move airplane1 up & move airplane2 down • Else move airplane1 down & airplane2 up

13. Alice: Events Alice Chapter 7 September 20, 2005

14. Yesterday • We looked at adding new functions • Remember, in Alice functions have return values • We looked at doing a few slightly complicated statements within Alice • We finished with a function and a method • isTooClose - boolean function • avoidCollision - method • Let’s make sure we all “got” those

15. isTooClose • Need to know: aircraft1, aircraft2, minimumAllowedDistance • We will return a Boolean (true/false) answer • Here we need an if/else control structure • Check if absolute value of aircraft1.distanceAbove(aircraft2) < minimumAllowedDistance if so, return true, else return false

16. avoidCollision • Then the world.avoidCollision method could be called if the airplanes were too close • Would need to check which airplane was above the other • If airplane1 above, move airplane1 up & move airplane2 down • Else move airplane1 down & airplane2 up

17. Some Cool Things • RandomNumber (World Function>Random) • Returns a fractional value between 0 and 1 • More button allows you to choose minimum and maximum for randoms • More again allows you to specify only integer values • Random Numbers allow you to create random motion in an animation • OrientTo method - to have two objects move together, first you must synchronize their orientation • Vehicle property - one object can “ride” on another object • More lets you set duration, style, and asSeenBy • You can use an object as the vehicle for the camera • Making Objects Invisible • Use the opacity property or the isShowing property to change what is visible in the world

18. Checkpoint • Are we okay with everything thus far? • In Edit>Preferences, choose the General tab and switch the display to “Java Style in Color” • This will get you used to seeing things as they are in Java. • You need to restart Alice to make this change take effect. • How many of you have done Tutorials 2 & 3? • If you can (if you have access to a PC), do these tonight if you haven’t already done them

19. Interactive Programming • So far we have been writing sequential, non-interactive events • Before run-time we knew the exact sequence of what was going to happen in the animation • With events, we no longer know exactly what sequence of events will happen • We need to link events to a responding event handling method • All events are world-level because the world is listening for any event to happen

20. Initial Scene • Let’s start with our airplane world from yesterday and get rid of one of the flying vehicles • We will make an interactive flying simulation today

21. Keyboard Control • We use keyboard commands (instructions) to control what events happen • Designing a flying game - we may want • The spacebar to make the plan spin • The up arrow to move the plane forward • And so on

22. What to do1: Create Methods • First write the methods that will respond to events • These can be world-level or class-level methods, depending on what makes sense in the given situation • biplane.flyForward • Move forward 2 meters for 2.5 seconds abruptly • Biplane.barrel • Roll right 1 revolution abruptly for 2.5 seconds

23. What to do2: Link Events • Linking events • In the upper right corner is the “Events editor” window • You can “create new event” and select event type from popup menu • “when a key is typed” • You will see “any key” and “nothing” as placeholders for what should happen • Lets create our first event: • When up is typed • Do biplane --> flyForward • Our second event” • When space is typed • Do biplane --> barrel

24. What to do3: Test • Run the program and make sure nothing happens until up arrow or spacebar are pressed • But you should also make sure that the event handling methods work as you expected after you develop them

25. Events & Parameters • What if we want the mouse to control what happens - like if the mouse clicks on an object, we want that object to do something • Obviously, we need parameters! • Let’s say we were building a rescue mission with a firetruck and a burning building with a person stuck on each of the three floors • We want the user to click on a person and then have the firetruck rescue that person • The save person method would need to know whichFloor the person was on, whichPerson to save, and howFar to move the ladder up

26. Burning Buildings • First we make a method, firetruck.savePerson with 3 parameters • whichFloor (so we know where to point the swivel to) • howFar (so we know how far to move the ladder forward) • whichPerson (so we know which person to move down the ladder) • So we could create a new mouse event that when a user clicks on randomGirl3 (who lives on the 3rd floor), we would automatically be able to set the other parameters to call savePerson with: • firetruck.savePerson(whichFloor = building.thirdFloor, whichPerson = randomGirl3, howFar = 3) • Testing - make sure to try all the possible combinations to make sure that the program works as expected

27. Other Alice Controls • The While Loop is a conditional loop, which only perform what is inside if a given condition is true • The Begin-During-End event • While: The conditional expression/function • Begin: Done once, at the time the condition is true • During: Put in the instructions or method that is done repeatedly as long as condition remains true • End: Done once, at the time the condition becomes false • Dummy Objects - Can be used to mark locations where the camera will be used • Could set up a “frontView” camera and a “backView” camera and change the point of view to these dummy views

28. The Wrath of Zeus • Demonstration of an event-driven world • Was going to be the basis of your project, but several components of the environment were missing in this version of Alice • Still it shows the beginning of the scope of the project you should be doing

29. Alice Project • We have learned most of the fundamental concepts available in Alice for programming • (Just not: infinite loops, lists, recursion, arrays, advanced use of variables) • Now we are going to put it all together to make a big program • See handout • Note: We have a quiz scheduled for this week - it’ll be on the concepts we’ve covered so far and will be on Monday

30. Project Work • Wednesday - Ideas due • Thursday & Friday: Class time on project • Friday: Brief quiz review