Using Cos & Sin to Drive a Car

Moving Car
Play demo

This is a basic driving simulation. A simple driving demonstration allow the player to steer and move.

Top-Down Driving Game

Click here to play

This is sample of a game that use Math.cos and Math.sin values of the rotation to determine forward movement, using left and right arrow keys to directly change the rotation property of the car.

Here is the start of the Moving Car class, with the listeners and the code to handle the arrow keys. Notice that we don't need any extra imports to use the Math functions. These are part of the standard ActionScript Library .


package {
import flash.display.*;
import flash.events.*;

public class MovingCar extends MovieClip {
private var leftArrow, rightArrow, upArrow: Boolean;

public function MovingCar() {

// move every frame
addEventListener(Event.ENTER_FRAME, moveCar);

// respond to key events
stage.addEventListener(KeyboardEvent.KEY_DOWN,keyPressedDown);
stage.addEventListener(KeyboardEvent.KEY_UP,keyPressedUp);
}

// set arrow variables to true
public function keyPressedDown(event:KeyboardEvent) {
if (event.keyCode == 37) {
leftArrow = true;
} else if (event.keyCode == 39) {
rightArrow = true;
} else if (event.keyCode == 38) {
upArrow = true;
}
}

// set arrow variables to false
public function keyPressedUp(event:KeyboardEvent) {
if (event.keyCode == 37) {
leftArrow = false;
} else if (event.keyCode == 39) {
rightArrow = false;
} else if (event.keyCode == 38) {
upArrow = false;
}
}

// turn or move car forward
public function moveCar(event:Event) {
if (leftArrow) {
car.rotation -= 5;
}
if (rightArrow) {
car.rotation += 5;
}
if (upArrow) {
moveForward();
}
}

// calculate x and y speed and move car
public function moveForward() {
var speed:Number = 5.0;
var angle:Number = 2*Math.PI*(car.rotation/360);
var dx:Number = speed*Math.cos(angle);
var dy:Number = speed*Math.sin(angle);
car.x += dx;
car.y += dy;
}
}
}

This source code is courtesy of ActionScript 3.0 Game Programming. I also use 2 reference books such as Learning ActionScript 3.0 and ActionScript 3.0 Bible.