“Hundreds” Flash game prototype using Box2D

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Did you play iOS Hundreds game? It’s basically the remake of Hundreds Flash game which wasn’t made with Box2D as far as I can see from the way it handles collisions, so we are going to improve it with the power of Box2D.

The aim of the game is simple: make the ball numbers increase to reach a hundred by touching it with the mouse. Do not grow balls when they touch each other.

In this first step, the game features are:

* There are a number of circles moving at a constant speed and colliding each other
* You can make a circle grow by touching it with the mouse

The prototype uses concepts we have already seen in other games, check the Filler Box2D prototype to make Box2D bodies move at a constant speed and the new Way of an Idea prototype to detect bodies under the mouse.

Here is the code:

package {
	import flash.display.Sprite;
	import flash.events.Event;
	import Box2D.Dynamics.*;
	import Box2D.Collision.*;
	import Box2D.Collision.Shapes.*;
	import Box2D.Common.Math.*;
	public class Main extends Sprite {
		private var world:b2World=new b2World(new b2Vec2(0,0),true);
		private var worldScale:Number=30;
		// speed of circles
		private var circleSpeed:Number=5;
		public function Main() {
			debugDraw();
			// adding 10 random circles
			for (var i:Number=1; i<=10; i++) {
				addCircle();
			}
			// adding boundary walls
			addWall(320,0,640,10);
			addWall(320,480,640,10);
			addWall(0,240,10,480);
			addWall(640,240,10,480);
			addEventListener(Event.ENTER_FRAME,update);
		}
		private function debugDraw():void {
			var debugDraw:b2DebugDraw=new b2DebugDraw();
			var debugSprite:Sprite=new Sprite();
			addChild(debugSprite);
			debugDraw.SetSprite(debugSprite);
			debugDraw.SetDrawScale(worldScale);
			debugDraw.SetFlags(b2DebugDraw.e_shapeBit|b2DebugDraw.e_jointBit);
			debugDraw.SetFillAlpha(0.5);
			world.SetDebugDraw(debugDraw);
		}
		private function addCircle():void {
			var bodyDef:b2BodyDef= new b2BodyDef();
			bodyDef.type=b2Body.b2_dynamicBody;
			bodyDef.position.Set(Math.round(Math.random()*600+20)/worldScale,Math.round(Math.random()*440+20)/worldScale);
			bodyDef.userData={name:"sphere"};
			var circleShape:b2CircleShape = new b2CircleShape(10/worldScale);
			var fixtureDef:b2FixtureDef = new b2FixtureDef();
			fixtureDef.density=1;
			fixtureDef.friction=0;
			fixtureDef.restitution=0.5;
			fixtureDef.shape=circleShape;
			var body:b2Body=world.CreateBody(bodyDef);
			body.CreateFixture(fixtureDef);
			// giving the circle a random direction
			var randomAngle:Number=Math.random()*2*Math.PI;
			body.SetLinearVelocity(new b2Vec2(circleSpeed*Math.cos(randomAngle),circleSpeed*Math.sin(randomAngle)));
		}
		private function addWall(pX:Number,pY:Number,w:Number,h:Number):void {
			var bodyDef:b2BodyDef=new b2BodyDef();
			bodyDef.position.Set(pX/worldScale,pY/worldScale);
			var polygonShape:b2PolygonShape=new b2PolygonShape();
			polygonShape.SetAsBox(w/2/worldScale,h/2/worldScale);
			var fixtureDef:b2FixtureDef=new b2FixtureDef();
			fixtureDef.shape=polygonShape;
			fixtureDef.density=1;
			fixtureDef.restitution=0.5;
			fixtureDef.friction=0;
			var theWall:b2Body=world.CreateBody(bodyDef);
			theWall.CreateFixture(fixtureDef);
		}
		// the core of the script, looking for the body touched and 
		// increasing the size of the circle shape
		private function queryCallback(fixture:b2Fixture):Boolean {
			var touchedBody:b2Body=fixture.GetBody();
			if (touchedBody.GetUserData()!=null) {
				var fixture:b2Fixture=touchedBody.GetFixtureList();
				var circleDef:b2CircleShape=fixture.GetShape() as b2CircleShape;
				var radius:Number=circleDef.GetRadius();
				// setting a max radius of 50 pixels for gameplay purpose
				if (radius<50/worldScale) {
					circleDef.SetRadius(radius+1/worldScale);
				}
			}
			return false;
		}
		private function update(e:Event):void {
			world.Step(1/30,10,10);
			world.ClearForces();
			for (var b:b2Body=world.GetBodyList(); b; b=b.GetNext()) {
				if (b.GetUserData()!=null) {
					// keep moving circles at a constant speed
					var velocity:b2Vec2=b.GetLinearVelocity();
					var speed:Number=velocity.Length();
					var ratio:Number=circleSpeed/speed;
					velocity.Multiply(ratio);
					b.SetLinearVelocity(velocity);
				}
			}
			// checking for bodies under the mouse
			world.QueryPoint(queryCallback,new b2Vec2(mouseX/worldScale,mouseY/worldScale));
			world.DrawDebugData();
		}
	}
}

In this prototype there is a limit to circle growth because I still have to check for collisions and I don't want circles to get bigger than the screen. This is the result:

Move the mouse over a circle to make it grow.

Download the source code.

Next time, the complete prototype with the count to 100 and the collision management.

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