Programming in Alice Chapter 2 Part 2

Events Editor Identifies what method is executed (run) when the “Play” button is hit 2

Deleting Instructions  Right-click the instruction and select delete  Drag the instruction tile to the trash can 3

Copying Instruction  Right-click the instruction and select make copy  Drag the instruction tile to the clipboard o When the clipboard turns green, drop the tile o Click on the clipboard and drag it back to the Method Editor 4

Objects With Custom Methods  In addition to primitive methods some objects have custom methods  When objects are selected from gallery, a listing of custom methods appears  Names of the custom methods give clues as to what the method does What do you think the foottap custom method does? 5

Naming Conventions  Names are known as identifiers because they identify items in a program  Use a name that provides meaning o Name of method should indicate the method’s purpose 6 Which one coaches the Knights and which one coaches the Cougars?

Naming Conventions  Dot notation o world.my first method  Dot (period) separates pieces of information o Left side: object that the method belongs to  The WORLD object in this case o Right side: name of the method  “my first method” in this case 7 the period is called a “dot”

8 Naming Conventions  Most programming languages do NOT recognize spaces o Alice allows spaces, good practice to not use them method.my first method  Without spaces, how do you have more than one word in names? o Lower case first letter o Capitalize first letter of next words o Called camelCase (camel’s hump) Note the space Which is easier to read? onehumpcamel or oneHumpCamel

Class Names  Method names begin with a lower case letter  Class names are capitalized  No spaces, so each word is capitalized o This convention is called PascalCase 9

Renaming  Objects o Right-click object’s tile in the object tree and select rename  Custom methods o Select the world object o Select the methods tab from the Details Panel o Right-click the my first method tile and select rename o If right-click does not work then hit Control & click 10

Orientation and Movement A translation in computer graphics o Moves an object a specified distance in a specified direction o Move instruction in Alice moves object  Left, right, up, down, forward, backward All movements of objects are egocentric o They move from their perspective, not ours 11

Pivot Point Examples Center of rotation 12

Turn Method Causes rotational motion Can turn an object o Left, right – similar to turning door on hinges  Along the horizontal plane o Forward, backward – lifting or closing hinged lid on a box  Along the vertical plane forward and backward 13

Roll Method Object is rotated left or right o Along the vertical plane clockwise or counter-clockwise Rotation depends on where center is 14

Subpart Rotation Center for rotational motion is where subpart connects to object o Also called a pivot point Turn rotation of Monkey’s left arm subpart 15

Orient to Method Used when two objects need to move together synchronization Objects might be pointing in different directions Use orient to method to align them o Argument is object to orient to method Forward Notice change orientation of ball changed 16

Circling Other Objects  Object’s turn method spins the object around o Can also get an object circle around another object  The asSeenBy optional argument causes an object to turn around the asSeenBy’s objects center point  Example: hawk turns one complete revolution around the tree from the tree’s perspective 17

Facing and Pointing Objects Turn to face o Causes object to turn toward another object Point at o Aligns two objects from the center of one to center of other o Centers are not always in good spot  They could collide in odd places or cause odd movement 18

“Move to” Instruction Moves an object to another object o Instead of a distance with move instruction The centers of both objects align They will look like they collide o Better to use “move toward” instruction o Need to know distance though and be careful of center Be very careful when “move toward” instruction o Will match center of both objects together o If centers are at different heights the object will be moved off ground or into ground to align centers o Use “turn to face” object then move distance to object 19

Exporting Code for Printing 20 Code can be exported to an HTML file From File – Choose Export Code for Printing You MUST add your name as the author o Author’s name is printed with the exported code Author’s name

Homework Read chapter 2 Answer questions in handout Do lab assignments after handing in algorithms Due one week after assigned with 1 week grace 21