CS320n –Visual Programming Class-level Methods and Inheritance – Part 2 Mike Scott (Slides 4-3-2) Thanks to Wanda Dann, Steve Cooper, and Susan Rodger for slides.

Class Level Methods - Part 2 What We Will Do Today Work on more class level methods Learn about built in functions Learn to use expressions Review the asSeenBy option Visual Programming Class Level Methods - Part 2

Guidelines for Class-Level Methods Should a method be a class-level method or a world-level method? For class level methods avoid hard coded references to other objects avoid calls to world level methods Play a sound only if has been imported and saved as part of the new class. (sounds can be imported to world or individual objects) If these guidelines are not followed and an instance of a class is added to another world, an error message is generated Visual Programming Class Level Methods - Part 2

Class Level Methods - Part 2 Bad Example 1 A class level method should not call world-level methods. Visual Programming Class Level Methods - Part 2

Class Level Methods - Part 2 Bad Example 2 Visual Programming Class Level Methods - Part 2

But I want to skate around things Is it reasonable to want a class-level method for the advanced skater where she skates around things? In this particular case, a penguin? Visual Programming Class Level Methods - Part 2

Class Level Methods - Part 2 Solution A solution is to write a class-level method with an object parameter that allows you to pass in the specific object. cleverSkater.skateAround Parameter: whichObject Do in order Do together cleverSkater turn to face whichObject cleverSkater lift right leg cleverSkater move to whichObject cleverSkater turn around whichObject Visual Programming Class Level Methods - Part 2

Parameterized Version of skateAround Making the object to skate around a parameter now removes the tie to the penguin in this world calling skateAround Visual Programming Class Level Methods - Part 2

Translating design into code Most of the skateAround storyboard design is straightforward and easy to code. The last two steps, however, require some thought: advancedSkater move to target -- What distance should the cleverSkater move? advancedSkater turn around target -- how do we tell cleverSkater to turn (in a circle) around another object? Visual Programming Class Level Methods - Part 2

Class Level Methods - Part 2 The distance to move We can work out how far to move the skater based on initial position of objects and a little experimentation Pick a distance, play the movie, more or less, refine until it looks good Is this a very general solution though? only works for one initial set up look to make it work for many set ups Visual Programming Class Level Methods - Part 2

Built-in Functions. (a.k.a. questions) The built-in function, distance to can be used to determine the distance the skater must move. Visual Programming Class Level Methods - Part 2

Class Level Methods - Part 2 Calling the Function drag and drop the function advancedSkater distance to from the function menu to the distance portion of the move method and pick expressions -> target call to move looks like this now Visual Programming Class Level Methods - Part 2

Class Level Methods - Part 2 Problem? What will happen when the skateAround method is called? Visual Programming Class Level Methods - Part 2

Class Level Methods - Part 2 Too Much Skater intersects penguin told to move forward the distance to the target moves skater all the way so centers of objects coincide distance measured center to center Visual Programming Class Level Methods - Part 2

Class Level Methods - Part 2 Expressions We don’t want the skater to move all the way to the target to avoid collision use math operator and create an expression that moves to within 2 meters Math operators is Alice: +, -, *, / Example: Visual Programming Class Level Methods - Part 2

Creating an Expression 1 3 2 4 Visual Programming Class Level Methods - Part 2

Class Level Methods - Part 2 More on Expressions Creating expressions with the pop up menus can be a pain In this case, text based programming languages may be easier to use Visual Programming Class Level Methods - Part 2

Class Level Methods - Part 2 Result of Expression Stops before running over penguin And skates around What if already less than 2 meters from an object? Visual Programming Class Level Methods - Part 2

Class Level Methods - Part 2 asSeenBy To have the skater skate around another object, pass whichObject as an argument to the asSeenBy parameter in a turn instruction. yes, passing a parameter to another method as a parameter For more details on asSeenBy, review Tips & Techniques 2. Visual Programming Class Level Methods - Part 2

Class Level Methods - Part 2 More on AsSeenBy Use invisible objects or dummy objects (isShowing property set to false) to have objects fly around in circles Example: Have gunfighters circle each other Visual Programming Class Level Methods - Part 2

Class Level Methods - Part 2 Circling Gunfighters Visual Programming Class Level Methods - Part 2

Class Level Methods - Part 2 Testing Each time you create a new class, test it: Add an instance of the new class to a new world. Write a short testing program to test each new method. Testing increases your confidence in the ability to reuse your code in other worlds. Visual Programming Class Level Methods - Part 2