# Basic Filler engine with Box2D – part 3

Read all posts about "" game

Here we are with the 3rd part… this time we’ll manage collision detection.

I recommend to read step 1 and 2 before continuing.

You should how to manage collisions with Box2D, and if not go and read Understanding how Box2D manages collisions, but this time we won’t use the collision handler.

Since all collisions we have to manage are among circles, I’ll simply use the Pythagoras theorem.

The only thing that differs from the original concept is when you touch a ball or the boundaries, the ball you are drawing does not disappear but falls down. Just to make something different…

```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.*;
public class colorballz extends Sprite {
public var m_dbgSprite;
public var m_world:b2World;
public var m_phys_scale:Number=30;
public var m_timestep:Number=1.0/30.0;
public var m_iterations:Number=10.0;
public var initX:Number=0.0;
public var initY:Number=0.0;
public var drawing:Boolean=false;
public var b:b2Body;
public var the_ball:ball;
public var the_enemy:enemy;
public function colorballz() {
var gravity:b2Vec2=new b2Vec2(0,9.8);
var worldAABB:b2AABB = new b2AABB();
worldAABB.lowerBound.Set(-1000,-1000);
worldAABB.upperBound.Set(1000,1000);
m_world=new b2World(worldAABB,gravity,true);
//Add Our Ground
AddStaticBox(250/m_phys_scale,510/m_phys_scale,250/m_phys_scale,10/m_phys_scale);
AddStaticBox(250/m_phys_scale,-10/m_phys_scale,250/m_phys_scale,10/m_phys_scale);
AddStaticBox(-10/m_phys_scale,250/m_phys_scale,10/m_phys_scale,250/m_phys_scale);
AddStaticBox(510/m_phys_scale,250/m_phys_scale,10/m_phys_scale,250/m_phys_scale);
//Add enemies
for (var x:int=1; x<=3; x++) {
// the first parameter is enemy's radius
addEnemy(10);
}
addEventListener(Event.ENTER_FRAME,Update);
stage.addEventListener(MouseEvent.MOUSE_DOWN,mousePressed);
stage.addEventListener(MouseEvent.MOUSE_MOVE,mouseMoved);
stage.addEventListener(MouseEvent.MOUSE_UP,mouseReleased);
}
public function mousePressed(e:MouseEvent) {
initX=e.localX;
initY=e.localY;
the_ball = new ball();
the_ball.x=mouseX;
the_ball.y=mouseY;
the_ball.width=1;
the_ball.height=1;
addChild(the_ball);
drawing=true;
}
public function mouseMoved(e:MouseEvent) {
if (drawing) {
the_ball.x=mouseX;
the_ball.y=mouseY;
}
}
public function mouseReleased(e:MouseEvent) {
if (drawing) {
drawing=false;
addCircle(mouseX,mouseY,the_ball.width/2,the_ball);
}
}
public function addCircle(_x:Number, _y:Number, _radius:Number,ballclip:ball) {
var bd:b2BodyDef = new b2BodyDef();
var cd:b2CircleDef = new b2CircleDef();
var area:Number=Math.floor(_radius*_radius*Math.PI/25)/100;
cd.radius=Math.abs(_radius)/m_phys_scale;
cd.density=2;
cd.restitution=0.7;
cd.friction=2;
bd.position.Set(_x/m_phys_scale, _y/ m_phys_scale);
bd.userData=ballclip;
b=m_world.CreateBody(bd);
b.CreateShape(cd);
b.SetMassFromShapes();
}
public function addEnemy(_radius:Number) {
var x_speed:Number=Math.random()*10;
var bd:b2BodyDef = new b2BodyDef();
var cd:b2CircleDef = new b2CircleDef();
the_enemy = new(enemy);
cd.radius=Math.abs(_radius)/m_phys_scale;
cd.density=20;
// setting restitution to 1 should grant the enemy won't lose speed when bouncing
// on STATIC objects
cd.restitution=1;
cd.friction=2;
// randomly placing the enemy
bd.position.Set((Math.random()*300+50)/m_phys_scale, (Math.random()*300+50)/ m_phys_scale);
bd.userData=the_enemy;
bd.userData.name="enemy";
bd.userData.width=_radius*2;
bd.userData.height=_radius*2;
addChild(the_enemy);
b=m_world.CreateBody(bd);
b.CreateShape(cd);
b.SetMassFromShapes();
// assigning random speed to enemy
b.m_linearVelocity.x=x_speed;
b.m_linearVelocity.y=10-x_speed;
}
public function AddStaticBox(_x:Number,_y:Number,_halfwidth:Number,_halfheight:Number) {
var bodyDef:b2BodyDef = new b2BodyDef();
bodyDef.position.Set(_x,_y);
var boxDef:b2PolygonDef = new b2PolygonDef();
boxDef.SetAsBox(_halfwidth,_halfheight);
boxDef.density=0.0;
var body:b2Body=m_world.CreateBody(bodyDef);
body.CreateShape(boxDef);
body.SetMassFromShapes();
}
public function Update(e:Event) {
var dist_x:Number;
var dist_y:Number;
var distance:Number;
// variable to handle enemy speed
var enemy_speed:Number;
// variable to handle the speed offset:it's the ratio between
// the real enemy speed and the minimum allowed speed
var speed_offset:Number;
if (drawing) {
the_ball.width+=2;
the_ball.height+=2;
// checking if the ball is touching boundaries
if (the_ball.x-the_ball.width/2<0||the_ball.x+the_ball.width/2>500||the_ball.y-the_ball.width/2<0||the_ball.y+the_ball.width/2>500) {
drawing=false;
addCircle(mouseX,mouseY,the_ball.width/2,the_ball);
}
}
m_world.Step(m_timestep,m_iterations);
for (var bb:b2Body=m_world.m_bodyList; bb; bb=bb.m_next) {
if (bb.m_userData is Sprite) {
if (bb.m_userData.name=="enemy") {
// determining enemy speed
enemy_speed=Math.abs(bb.GetLinearVelocity().x)+Math.abs(bb.GetLinearVelocity().y);
// if the speed is too slow... (lower than 10)
if (enemy_speed<10) {
// calculating the offset
speed_offset=10/enemy_speed;
// multiplying the horizontal and vertical components of the speed
// by the offset
bb.m_linearVelocity.x=bb.GetLinearVelocity().x*speed_offset;
bb.m_linearVelocity.y=bb.GetLinearVelocity().y*speed_offset;
}
}
bb.m_userData.x=bb.GetPosition().x*30;
bb.m_userData.y=bb.GetPosition().y*30;
// if I am drawing the ball...
if (drawing) {
// determining the distance between the current ball and the one I am drawing
dist_x=the_ball.x-bb.m_userData.x;
dist_y=the_ball.y-bb.m_userData.y;
// notice I am not using any square root to make the script lighter
distance=dist_x*dist_x+dist_y*dist_y;
// if balls collide...
if (distance<(the_ball.width/2+bb.m_userData.width/2)*(the_ball.width/2+bb.m_userData.width/2)) {
// release the drawing ball and set drawing to false, as if I released the mouse
// here you should lose a life...
drawing=false;
addCircle(mouseX,mouseY,the_ball.width/2,the_ball);
}
}
}
}
}
}
}```

And this is the result:

You should already know ho to play...

Download the source code and make your own filler game

215 GAME PROTOTYPES EXPLAINED WITH SOURCE CODE
// 1+2=3
// 10000000
// 2 Cars
// 2048
// Avoider
// Ballz
// Block it
// Blockage
// Bloons
// Boids
// Bombuzal
// BoxHead
// Breakout
// Bricks
// Columns
// CubesOut
// Dots
// DROP'd
// Dudeski
// Eskiv
// Filler
// Fling
// Globe
// HookPod
// Hundreds
// InkTd
// Iromeku
// Lumines
// Magick
// MagOrMin
// Maze
// Memdot
// Nano War
// Nodes
// o:anquan
// Ononmin
// Pacco
// Phyballs
// Platform
// Poker
// Pool
// Poux
// Pudi
// qomp
// Racing
// Radical
// Renju
// SameGame
// Security
// Sling
// Slingy
// Sokoban
// Splitter
// Sproing
// Stack
// Stairs
// Stringy
// Sudoku
// Tetris
// Threes
// Toony
// Turn
// TwinSpin
// vvvvvv
// Wordle
// Worms
// Yanga
// Zhed
// zNumbers