Box2D flying arrows engine – first attempt

December 14, 2012 • Actionscript 3, Box2D, Flash, Game design by Emanuele Feronato • 9 Comments

This is an uncommented and unoptimized attempt to make an arrow engine. I used the third example of my Flying arrows simulation with Box2D, added the lines to have the camera following the latest arrow fired taken from Develop a Flash game like Angry Birds using Box2D – Following bird with the camera and skinning crates and played with a custom contact listener to add different behaviors to arrow-wall collision, arrow-crate collision and arrow-arrow collision.

I got also inspired by iforce2D sticky projectiles, and this is what I made:

Click on the stage to shoot an arrow from x=50, y=240 according to the angle between such coordinate and mouse pointer.

This is the main class:

package {
	import flash.display.Sprite;
	import flash.events.Event;
	import flash.events.MouseEvent;
	import Box2D.Dynamics.*;
	import Box2D.Collision.*;
	import Box2D.Collision.Shapes.*;
	import Box2D.Common.Math.*;
	import Box2D.Dynamics.Contacts.*;
	public class Main extends Sprite {
		private var world:b2World=new b2World(new b2Vec2(0,10),true);
		private var worldScale:int=30;
		private var arrowVector:Vector.<b2Body>=new Vector.<b2Body>();
		private var customContact=new CustomContactListener();
		public function Main():void {
			world.SetContactListener(customContact);
			debugDraw();
			wall(640,470,1280,20);
			wall(1270,240,20,4800);
			for (var i:Number=1; i<=10; i++) {
				crate(Math.random()*500+640,Math.random()*400,80,80);
			}
			addEventListener(Event.ENTER_FRAME, update);
			stage.addEventListener(MouseEvent.CLICK,addArrow);
		}
		private function addArrow(e:MouseEvent):void {
			var angle:Number=Math.atan2(mouseY-240,mouseX-50);
			var vertices:Vector.<b2Vec2>=new Vector.<b2Vec2>();
			vertices.push(new b2Vec2(-1.4,0));
			vertices.push(new b2Vec2(0,-0.1));
			vertices.push(new b2Vec2(0.6,0));
			vertices.push(new b2Vec2(0,0.1));
			var bodyDef:b2BodyDef= new b2BodyDef();
			bodyDef.position.Set(50/worldScale,240/worldScale);
			bodyDef.type=b2Body.b2_dynamicBody;
			bodyDef.userData={name:"arrow",freeFlight:false,follow:true};
			bodyDef.bullet=true;
			var polygonShape:b2PolygonShape = new b2PolygonShape();
			polygonShape.SetAsVector(vertices,4);
			var fixtureDef:b2FixtureDef = new b2FixtureDef();
			fixtureDef.shape=polygonShape;
			fixtureDef.density=1;
			fixtureDef.friction=0.5;
			fixtureDef.restitution=0.5;
			var body:b2Body=world.CreateBody(bodyDef);
			body.CreateFixture(fixtureDef);
			body.SetLinearVelocity(new b2Vec2(30*Math.cos(angle),30*Math.sin(angle)));
			body.SetAngle(angle);
			for (var i:Number=0; i<arrowVector.length; i++) {
				arrowVector[i].GetUserData().follow=false;
			}
			arrowVector.push(body);
		}
		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 wall(pX:Number,pY:Number,w:Number,h:Number):void {
			var bodyDef:b2BodyDef=new b2BodyDef();
			bodyDef.position.Set(pX/worldScale,pY/worldScale);
			bodyDef.userData={name:"wall"};
			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=0.4;
			fixtureDef.friction=0.5;
			var theWall:b2Body=world.CreateBody(bodyDef);
			theWall.CreateFixture(fixtureDef);
		}
		private function crate(pX:Number,pY:Number,w:Number,h:Number):void {
			var bodyDef:b2BodyDef=new b2BodyDef();
			bodyDef.position.Set(pX/worldScale,pY/worldScale);
			bodyDef.userData={name:"crate"};
			bodyDef.type=b2Body.b2_dynamicBody;
			var polygonShape:b2PolygonShape=new b2PolygonShape();
			polygonShape.SetAsBox(w/2/worldScale,h/2/worldScale);
			var fixtureDef:b2FixtureDef=new b2FixtureDef();
			fixtureDef.shape=polygonShape;
			fixtureDef.density=0.2;
			fixtureDef.restitution=0.4;
			fixtureDef.friction=0.5;
			var theWall:b2Body=world.CreateBody(bodyDef);
			theWall.CreateFixture(fixtureDef);
		}
		private function update(e : Event):void {
			world.Step(1/30,5,5);
			world.ClearForces();
			for (var i:Number=arrowVector.length-1; i>=0; i--) {
				var body:b2Body=arrowVector[i];
				if (body.GetType()==b2Body.b2_dynamicBody) {
					if (! body.GetUserData().freeFlight) {
						var flyingAngle:Number=Math.atan2(body.GetLinearVelocity().y,body.GetLinearVelocity().x);
						body.SetAngle(flyingAngle);
					}
				}
				else {
					arrowVector.splice(i,1);
					body.SetBullet(false);
					body.GetUserData().follow=false;
				}
				if (body.GetUserData().follow) {
					var posX:Number=body.GetPosition().x*worldScale;
					posX=stage.stageWidth/2-posX;
					if (posX>0) {
						posX=0;
					}
					if (posX<-640) {
						posX=-640;
					}
					x=posX;
				}
			}
			world.DrawDebugData();
		}
	}
}

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package {

import flash.display.Sprite;

import flash.events.Event;

import flash.events.MouseEvent;

import Box2D.Dynamics.*;

import Box2D.Collision.*;

import Box2D.Collision.Shapes.*;

import Box2D.Common.Math.*;

import Box2D.Dynamics.Contacts.*;

public class Main extends Sprite {

private var world:b2World=new b2World(new b2Vec2(0,10),true);

private var worldScale:int=30;

private var arrowVector:Vector.<b2Body>=new Vector.<b2Body>();

private var customContact=new CustomContactListener();

public function Main():void {

world.SetContactListener(customContact);

debugDraw();

wall(640,470,1280,20);

wall(1270,240,20,4800);

for (var i:Number=1; i<=10; i++) {

crate(Math.random()*500+640,Math.random()*400,80,80);

}

addEventListener(Event.ENTER_FRAME, update);

stage.addEventListener(MouseEvent.CLICK,addArrow);

}

private function addArrow(e:MouseEvent):void {

var angle:Number=Math.atan2(mouseY-240,mouseX-50);

var vertices:Vector.<b2Vec2>=new Vector.<b2Vec2>();

vertices.push(new b2Vec2(-1.4,0));

vertices.push(new b2Vec2(0,-0.1));

vertices.push(new b2Vec2(0.6,0));

vertices.push(new b2Vec2(0,0.1));

var bodyDef:b2BodyDef= new b2BodyDef();

bodyDef.position.Set(50/worldScale,240/worldScale);

bodyDef.type=b2Body.b2_dynamicBody;

bodyDef.userData={name:"arrow",freeFlight:false,follow:true};

bodyDef.bullet=true;

var polygonShape:b2PolygonShape = new b2PolygonShape();

polygonShape.SetAsVector(vertices,4);

var fixtureDef:b2FixtureDef = new b2FixtureDef();

fixtureDef.shape=polygonShape;

fixtureDef.density=1;

fixtureDef.friction=0.5;

fixtureDef.restitution=0.5;

var body:b2Body=world.CreateBody(bodyDef);

body.CreateFixture(fixtureDef);

body.SetLinearVelocity(new b2Vec2(30*Math.cos(angle),30*Math.sin(angle)));

body.SetAngle(angle);

for (var i:Number=0; i<arrowVector.length; i++) {

arrowVector[i].GetUserData().follow=false;

}

arrowVector.push(body);

}

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 wall(pX:Number,pY:Number,w:Number,h:Number):void {

var bodyDef:b2BodyDef=new b2BodyDef();

bodyDef.position.Set(pX/worldScale,pY/worldScale);

bodyDef.userData={name:"wall"};

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=0.4;

fixtureDef.friction=0.5;

var theWall:b2Body=world.CreateBody(bodyDef);

theWall.CreateFixture(fixtureDef);

}

private function crate(pX:Number,pY:Number,w:Number,h:Number):void {

var bodyDef:b2BodyDef=new b2BodyDef();

bodyDef.position.Set(pX/worldScale,pY/worldScale);

bodyDef.userData={name:"crate"};

bodyDef.type=b2Body.b2_dynamicBody;

var polygonShape:b2PolygonShape=new b2PolygonShape();

polygonShape.SetAsBox(w/2/worldScale,h/2/worldScale);

var fixtureDef:b2FixtureDef=new b2FixtureDef();

fixtureDef.shape=polygonShape;

fixtureDef.density=0.2;

fixtureDef.restitution=0.4;

fixtureDef.friction=0.5;

var theWall:b2Body=world.CreateBody(bodyDef);

theWall.CreateFixture(fixtureDef);

}

private function update(e : Event):void {

world.Step(1/30,5,5);

world.ClearForces();

for (var i:Number=arrowVector.length-1; i>=0; i--) {

var body:b2Body=arrowVector[i];

if (body.GetType()==b2Body.b2_dynamicBody) {

if (! body.GetUserData().freeFlight) {

var flyingAngle:Number=Math.atan2(body.GetLinearVelocity().y,body.GetLinearVelocity().x);

body.SetAngle(flyingAngle);

}

else {

arrowVector.splice(i,1);

body.SetBullet(false);

body.GetUserData().follow=false;

}

if (body.GetUserData().follow) {

var posX:Number=body.GetPosition().x*worldScale;

posX=stage.stageWidth/2-posX;

if (posX>0) {

posX=0;

}

if (posX<-640) {

posX=-640;

}

x=posX;

}

world.DrawDebugData();

}

and this is the custom contact listener:

package {
	import Box2D.Dynamics.*;
	import Box2D.Collision.*;
	import Box2D.Dynamics.Joints.*;
	import Box2D.Dynamics.Contacts.*;
	import Box2D.Common.Math.b2Vec2;
	class CustomContactListener extends b2ContactListener {
		override public function PreSolve(contact:b2Contact, oldManifold:b2Manifold):void {
			var contactPoint:b2Vec2;
			var weldJointDef:b2WeldJointDef;
			if (contact.IsTouching()) {
				var bodyA:b2Body=contact.GetFixtureA().GetBody();
				var bodyB:b2Body=contact.GetFixtureB().GetBody();
				var objA:Object=bodyA.GetUserData();
				var objB:Object=bodyB.GetUserData();
				if (objA.name=="arrow"&&objB.name=="arrow") {
					for (var j:b2JointEdge=bodyA.GetJointList(); j; j=j.next) {
						bodyA.GetWorld().DestroyJoint(j.joint);
					}
					for (j=bodyB.GetJointList(); j; j=j.next) {
						bodyB.GetWorld().DestroyJoint(j.joint);
					}
				}
				if (objA.name=="wall"&&objB.name=="arrow") {
					if (! objB.freeFlight) {
						weldJointDef = new b2WeldJointDef();
						weldJointDef.Initialize(bodyB,bodyA,bodyA.GetWorldCenter());
						bodyB.GetWorld().CreateJoint(weldJointDef);
					}
				}
				if (objB.name=="wall"&&objA.name=="arrow") {
					if (! objA.freeFlight) {
						weldJointDef = new b2WeldJointDef();
						weldJointDef.Initialize(bodyA,bodyB,bodyB.GetWorldCenter());
						bodyA.GetWorld().CreateJoint(weldJointDef);
					}
				}
				if (objA.name=="crate"&&objB.name=="arrow") {
					contactPoint=contact.GetManifold().m_points[0].m_localPoint;
					if (! objB.freeFlight&&Math.round(contactPoint.x*10)==6) {
						weldJointDef = new b2WeldJointDef();
						weldJointDef.Initialize(bodyB,bodyA,bodyA.GetWorldCenter());
						bodyB.GetWorld().CreateJoint(weldJointDef);
					}
				}
				if (objB.name=="crate"&&objA.name=="arrow") {
					contactPoint=contact.GetManifold().m_points[0].m_localPoint;
					if (! objA.freeFlight&&Math.round(contactPoint.x*10)==6) {
						weldJointDef = new b2WeldJointDef();
						weldJointDef.Initialize(bodyA,bodyB,bodyB.GetWorldCenter());
						bodyA.GetWorld().CreateJoint(weldJointDef);
					}
				}
				if (objB.name=="arrow") {
					objB.freeFlight=true;
				}
				if (objA.name=="arrow") {
					objA.freeFlight=true;
				}
			}
		}
	}
}

package {

import Box2D.Dynamics.*;

import Box2D.Collision.*;

import Box2D.Dynamics.Joints.*;

import Box2D.Dynamics.Contacts.*;

import Box2D.Common.Math.b2Vec2;

class CustomContactListener extends b2ContactListener {

override public function PreSolve(contact:b2Contact, oldManifold:b2Manifold):void {

var contactPoint:b2Vec2;

var weldJointDef:b2WeldJointDef;

if (contact.IsTouching()) {

var bodyA:b2Body=contact.GetFixtureA().GetBody();

var bodyB:b2Body=contact.GetFixtureB().GetBody();

var objA:Object=bodyA.GetUserData();

var objB:Object=bodyB.GetUserData();

if (objA.name=="arrow"&&objB.name=="arrow") {

for (var j:b2JointEdge=bodyA.GetJointList(); j; j=j.next) {

bodyA.GetWorld().DestroyJoint(j.joint);

}

for (j=bodyB.GetJointList(); j; j=j.next) {

bodyB.GetWorld().DestroyJoint(j.joint);

}

if (objA.name=="wall"&&objB.name=="arrow") {

if (! objB.freeFlight) {

weldJointDef = new b2WeldJointDef();

weldJointDef.Initialize(bodyB,bodyA,bodyA.GetWorldCenter());

bodyB.GetWorld().CreateJoint(weldJointDef);

}

if (objB.name=="wall"&&objA.name=="arrow") {

if (! objA.freeFlight) {

weldJointDef = new b2WeldJointDef();

weldJointDef.Initialize(bodyA,bodyB,bodyB.GetWorldCenter());

bodyA.GetWorld().CreateJoint(weldJointDef);

}

if (objA.name=="crate"&&objB.name=="arrow") {

contactPoint=contact.GetManifold().m_points[0].m_localPoint;

if (! objB.freeFlight&&Math.round(contactPoint.x*10)==6) {

weldJointDef = new b2WeldJointDef();

weldJointDef.Initialize(bodyB,bodyA,bodyA.GetWorldCenter());

bodyB.GetWorld().CreateJoint(weldJointDef);

}

if (objB.name=="crate"&&objA.name=="arrow") {

contactPoint=contact.GetManifold().m_points[0].m_localPoint;

if (! objA.freeFlight&&Math.round(contactPoint.x*10)==6) {

weldJointDef = new b2WeldJointDef();

weldJointDef.Initialize(bodyA,bodyB,bodyB.GetWorldCenter());

bodyA.GetWorld().CreateJoint(weldJointDef);

}

if (objB.name=="arrow") {

objB.freeFlight=true;

}

if (objA.name=="arrow") {

objA.freeFlight=true;

}

Next time, I’ll add some improvements like a real bow firing arrow at different speed. Meanwhile feel free to give feedback or suggestions.

Rate this post: 1 Star

(21 votes, average: 5.00 out of 5)

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This post has 9 comments

Cody

on December 14, 2012 at 3:29 pm

This is truly great, you are an inspiration!
André Fellipe

on December 14, 2012 at 5:07 pm

Awesome! Some little optimizations and it will be perfect!
[??]Box2D????-???? » Luo????

on December 15, 2012 at 3:09 pm

[...] ?????http://www.emanueleferonato.com/2012/12/14/box2d-flying-arrow-engine-first-attempt/ [...]
MC

on December 15, 2012 at 9:50 pm

Suggestions:
- zoom in / zoom out / cam-movement
- Control the arrow speed/power
- graphic textures
Box2D flying arrows engine – first attempt – Emanuele Feronato « eaflash

on December 17, 2012 at 10:36 am

[...] on http://www.emanueleferonato.com Share this:TwitterFacebookLike this:LikeBe the first to like [...]
Shekhar Suman

on December 17, 2012 at 11:26 pm

Please check my website. I’ve tried to accomplish the same using Box2dWeb.
http://adf.ly/G5gMb
Husky

on December 18, 2012 at 4:27 am

This is COOL!!!!!!!
Franklin

on January 2, 2013 at 5:56 am

@MC plus one for the suggestions
Ray Kutro

on March 1, 2013 at 1:53 pm

Great stuff really… I’m waiting for the next part with real bow. Thanks

Emanuele Feronato

italian geek and PROgrammer

Box2D flying arrows engine – first attempt

This post has 9 comments

Cody

André Fellipe

[??]Box2D????-???? » Luo????

MC

Box2D flying arrows engine – first attempt – Emanuele Feronato « eaflash

Shekhar Suman

Husky

Franklin

Ray Kutro