Computer Game Design 101

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ActionScript is…

• Object-oriented programming

• Everything you do in ActionScript does something to some object*

• Some objects are called Symbols in Flash– Movie Clip– Graphic– Button

*anything you can manipulate in some way

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Object oriented?

• You can decide what happens when a user clicks a button without worrying about how the button (or program) knows that it has been clicked

• You can decide what changes to make to an object’s properties without knowing the internal mechanics of how those changes were made

• You can program tasks incrementally without sitting down and writing the whole program from start to finish in one session

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ActionScript Deconstructed

• Class: a group of items that are similar in some way– Items are called objects or instances of the class

• Objects can be concrete (like a button or graphic) or abstract (like a variable that is invisible, but hold data)

• Objects have two aspects form (properties) and function (methods)

• Each property and method is defined by Actions (pieces of code that tell Flash how to manipulate a target object at any point in your movie).

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ActionScript Metaphor

• Ball could be considered a class of items defined as “spherical things”– One object in this class is a movie clip called

Tennis_ball• The properties of Tennis_ball might be the color

neon green or a 20-pixel diameter• Its methods might be bounce, roll, and/or spin

– A 2nd object in the ball class might be Softball• Properties white…etc.

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ActionScript Flow

• Flash executes ActionScript statements starting with the first statement and continuing in order until it reaches the final statement or a statement that instructs ActionScript to go somewhere else.

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One type of action that sends ActionScript somewhere

other than the next statement is an if statement

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Actions

• Tell Flash to do something– Frame actions – Object actions

• Actions also can have parameters

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gotoAndPlay

• This frame action sends the playhead to the specified frame in a scene and plays from that frame. If no scene is specified, the playhead goes to the specified frame in the current scene.

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Functions

• Perform a specific task

• Like in a spreadsheet program (Excel)

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getVersion

• Returns the Flash Player version number and operating system information.

• You can use this function to determine whether the Flash Player that is in use can handle your Actionscript.

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Properties

• All available information about an object

• You can use ActionScript to read and modify object properties

• All property names begin with an underscore (e.g., _visible)

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_visible = false

• This property make an object invisible

• Assign the following action to a button…On (release) {

_visible = false;

}

• Button disappears on mouse click

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Method

• Similar to actions in that they effect objects

• Built into objects

• Invoked (Executed) through dot notation

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RocketMC.gotoAndPlay(“BlastOff”);

• ActionScript notation must end in ;

• Movie clip Rocket MC goes to a frame labeled BlastOff and plays

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Variables

• hold data for use in your Flash movies

• Variables can hold any type of data

• You could store:– User name– Result of calculation– True or false value

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Expressions

• An expression is any statement that Flash can evaluate and that returns a value.

• You can create an expression by combining operators and values or by calling a function.

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Operators

• Expressions use operators to tell Flash how to manipulate the values in the expression.

• They are the commands that say “add these values” or “multiply these numbers”

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Some types of operators

• Assignment: • are used to assign values to variables. • The most common is (=). It makes the variable on

the left equal to the value of the variable or expression on the right.

• Comparison and equivalence: • (<), (>), (< =)

• Numeric: • perform mathematical operations on values

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Looping

• When you need to repeat certain actions in your movies more than once.

• Makes coding more efficient, using the same set of commands as many times as necessary to complete a task.

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Looping examples

• while• Creates a loop that continues to repeat as long as

a condition remains true

• for• Creates a loop that executes a specific number of

times using a counter

• for…in• Creates a loop that executes once for each

member of a group of objects (class)• This makes certain that the entire group of objects

is processed in the same way

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Hints

• Before you begin writing scripts, formulate your goal and understand what you want to achieve.

• Planning your scripts is as important as developing storyboards for your work.

• Start by writing out what you want to happen in the movie, as in this example: – I want to create my whole site using Flash. – Site visitors will be asked for their name, which will be reused in

messages throughout the site. – The site will have a draggable navigation bar with buttons that

link to each section of the site. – When a navigation button is clicked, the new section will fade in

at the center of the Stage. – One scene will have a contact form with the user's name already

filled in.