Emanuele Feronato

italian geek and PROgrammer

Talking about Pixel Purge game, Actionscript 3, Flash and Game development.

In step 1 I showed you how to move your spaceship, now it’s time to fire some bullets.

First, we need to more objects: the crosshair, called crosshair_mc, and the bullet itself, called bullet_mc.

Firing is very easy, as all you need to do is keeping the mouse button pressed. In the original game there is also a fire ratio and a different amount of bullets fired at the same time, but we’ll see these features later, when we’ll manage powerups.

At the moment, main class changes this way:

package {
	import flash.display.Sprite;
	import flash.events.Event;
	import flash.events.KeyboardEvent;
	import flash.events.MouseEvent;
	import flash.geom.Point;
	public class main extends Sprite {
		private var game_container:game_container_mc;
		private var player:player_mc;
		private var left,up,right,down:Boolean;
		private var crosshair:crosshair_mc;
		private var firing:Boolean=false;
		private var bullet:bullet_mc;
		public function main() {
			left=up=right=down=false;
			game_container=new game_container_mc();
			addChild(game_container);
			player=new player_mc();
			game_container.addChild(player);
			crosshair=new crosshair_mc();
			addChild(crosshair);
			stage.addEventListener(KeyboardEvent.KEY_DOWN,on_key_down);
			stage.addEventListener(KeyboardEvent.KEY_UP,on_key_up);
			addEventListener(Event.ENTER_FRAME,on_enter_frame);
			addEventListener(MouseEvent.MOUSE_DOWN,on_mouse_down);
			addEventListener(MouseEvent.MOUSE_UP,on_mouse_up);
		}
		private function on_mouse_down(e:MouseEvent):void {
			firing=true;
		}
		private function on_mouse_up(e:MouseEvent):void {
			firing=false;
		}
		private function on_enter_frame(e:Event):void {
			crosshair.x=mouseX;
			crosshair.y=mouseY;
			if (left) {
				player.engine(-1,0);
			}
			if (right) {
				player.engine(1,0);
			}
			if (up) {
				player.engine(0,-1);
			}
			if (down) {
				player.engine(0,1);
			}
			player.move_player();
			game_container.move_container(player.x,player.y);
			if (firing) {
				var dist_x:Number=player.x+game_container.x-mouseX;
				var dist_y:Number=player.y+game_container.y-mouseY;
				bullet=new bullet_mc(player.x,player.y,Math.atan2(dist_y,dist_x));
				game_container.addChild(bullet);
			}
		}
		private function on_key_down(e:KeyboardEvent):void {
			switch (e.keyCode) {
				case 37 ://left
					left=true;
					break;
				case 38 :// up
					up=true;
					break;
				case 39 ://right
					right=true;
					break;
				case 40 ://down
					down=true;
					break;
			}
		}
		private function on_key_up(e:KeyboardEvent):void {
			switch (e.keyCode) {
				case 37 ://left
					left=false;
					break;
				case 38 :// up
					up=false;
					break;
				case 39 ://right
					right=false;
					break;
				case 40 ://down
					down=false;
					break;
			}
		}
		public function remove_bullet(b:bullet_mc):void {
			game_container.removeChild(b);
			b=null;
		}
	}
}

firing variable will decide whether I am firing or not and at lines 51-56 will generate the bullets.

bullet_mc constructor works with three arguments: x position, y position and the angle of shooting, calculated with trigonometry.

bullet_mc class also uses trigonometry to make the bullet fly:

package {
	import flash.display.Sprite;
	import flash.events.Event;
	public class bullet_mc extends Sprite {
		private var speed:uint=20;
		private var shooting_angle:Number;
		public function bullet_mc(px:int,py:int,angle:Number) {
			x=px;
			y=py;
			shooting_angle=angle;
			addEventListener(Event.ENTER_FRAME,on_enter_frame);
		}
		private function on_enter_frame(e:Event) {
			x-=speed*Math.cos(shooting_angle);
			y-=speed*Math.sin(shooting_angle);
			if (x>1280||x<0||y>960||y<0) {
				removeEventListener(Event.ENTER_FRAME,on_enter_frame);
				var par:main= this.parent.parent as main
				par.remove_bullet(this);
			}
		}
	}
}

There's nothing you haven't already seen in the blog, just combined in a different way.

This is the result:

Move the ship with arrow keys, aim and fire with the mouse.

Download the source code.