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 Tutorials » Games
The CodingThere are a few important pieces of ActionScript that help in making this a fairly realistic space flight simulation. For the sake of not getting confused, we'll deal with each object to be scripted seperately. There are four objects which need ActionScript added to them. These are "player1", "planet1", "starfield1", and "bigstars1". First, let's deal with player1, the target that will sit in the center of the viewscreen. To center the target, enter the following code in the player1 instance's Action box:
onClipEvent(load)
{
this._x = 250;
this._y = 200;
planetSpeed=(.02 * _root.planet1._width);
starSpeed=(.001 * _root.planet1._width);
bigstarSpeed=(.003 * _root.planet1._width);
}
onClipEvent (enterFrame)
{
if (Key.isDown(Key.RIGHT))
{
_root.planet1._x -= planetSpeed;
_root.starfield1._x -= starSpeed;
_root.bigstars1._x -= bigstarSpeed;
}
else if (Key.isDown(Key.LEFT))
{
_root.planet1._x += planetSpeed;
_root.starfield1._x += starSpeed;
_root.bigstars1._x += bigstarSpeed;
}
if (Key.isDown(Key.DOWN))
{
_root.planet1._y -= planetSpeed;
_root.starfield1._y -= starSpeed;
_root.bigstars1._y -= bigstarSpeed;
}
else if (Key.isDown(Key.UP))
{
_root.planet1._y += planetSpeed;
_root.starfield1._y += starSpeed;
_root.bigstars1._y += bigstarSpeed;
}
}
Most of this code is pretty straight-forward, but it's worth going over. First, in the (load)
section at the top of the script, we center the object at the coordinates 250,200 and introduce
our three speed variables: planetSpeed is the rate at which the planet object seems to
move relative to the player. starSpeed sets how quickly the smaller stars appear to move,
and bigstarSpeed sets that speed for the big stars. As you can see, all three of these
variables depend ultimately on the _width property of the planet1 object. In other words, as the
planet object grows (or seems to get closer), the other objects' movements are affected, just
as if they were actually getting closer to the player in a space environment. After the (load)
section is (enterFrame), which updates every time the object takes any action. This section
consists of four keystroke handlers, one for each of the arrow keys. When each arrow key is
pushed, all three objects will react according to the variables set earlier.
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Programming Starfields for Realistic 3D Space Flight
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