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.
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