TUTORIAL: Building games in Flash 5
Part 1: Player movement and fire.

Author: David Doull
Date: 23/02/01
Download source files: tut1.zip

Step 2: Right, now lets get the spaceship moving!

The player will use the arrow keys to move the spaceship, up, down, left and right. So how do we do this?

We need to detect which key or keys are being pressed using Key.isDown and then adjust the spaceship x-position and y-postion accordingly.

Show me the code.

Lets have a look at how this is done. We are going to put almost all of the game code in clip events so if you don't know what clip events are then read on. (If you already know all about clip events then skip the next three paragraphs)

What are Clip Events?

Put simply, an event is 'something that happens', so a clip event is something that happens to a movie clip. More precisely it is an event that is associated with a movie clip. Two of the most useful movie clip events are 'load' and 'enterFrame' which occur when a movie clip is loaded and when it it enters a frame. The code looks like this

onClipEvent(load){

// code goes here

}

Any code contained between the curly brackets will be run when the movie clip is loaded or first appears on the stage. The load event is useful in games for initialising variables and defining functions, anything you want to do once at the start of a game - like setting the score to zero. The 'enterFrame' event occurs every time the movie clip enters a new frame. So code you want to happen over and over again (such as detecting a collision) should be included in an enterFrame event.

Where do you type this clip event code? Select the movieclip and either right click and choose actions, or pick actions from the Window menu, the actions window will open and this is where you type your clipEvent code. This is similar to where you put code for buttons in Flash 4.

Setting the speed.

Right click on the spaceship movie clip and choose actions. In the actions window type

onClipEvent(load){

moveSpeed=10;

}

This sets a variable called moveSpeed to 10 when the spaceship is first loaded. This variable will control the number of pixels the player moves. So to make the player appear to move faster you would change this to a higher number.

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