Real world catapult prototype using Box2D – Cleaner code

Read all posts about "" game

We got it.

After the first catapult prototype and the “slippery wheels” sequel, this is a version with realistic movement and a lot cleaner code.

To add realistic movement I defined friction and restitution, making useless the CreateFixture2 function and widely using the more appropriate CreateFixture one.

This way I have full control on fixtures, while in the old way I could only define their masses.

This is the result:

Left and right to move, spacebar to fire

And this is the code:

package {
	import flash.display.Sprite;
	import flash.events.Event;
	import flash.events.KeyboardEvent;
	import Box2D.Dynamics.*;
	import Box2D.Collision.*;
	import Box2D.Collision.Shapes.*;
	import Box2D.Common.Math.*;
	import Box2D.Dynamics.Joints.*;
	public class main extends Sprite {
		public var world:b2World=new b2World(new b2Vec2(0,10.0),true);
		public var world_scale:int=30;
		var catapult_chassis_body:b2Body;
		var catapult_arm_body:b2Body;
		var rear_wheel_body:b2Body;
		var front_wheel_body:b2Body;
		var arm_revolute_joint:b2RevoluteJoint;
		var front_wheel_revolute_joint:b2RevoluteJoint;
		var rear_wheel_revolute_joint:b2RevoluteJoint;
		var left_key_pressed:Boolean=false;
		var right_key_pressed:Boolean=false;
		public function main():void {
			debug_draw();
			the_ground();
			the_catapult_body();
			the_catapult_arm();
			the_catapult_motor();
			the_wheels();
			the_wheel_motors();
			the_cannonball();
			addEventListener(Event.ENTER_FRAME, update);
			stage.addEventListener(KeyboardEvent.KEY_DOWN, key_down);
			stage.addEventListener(KeyboardEvent.KEY_UP, key_up);
		}
		public function the_cannonball():void {
			var cannonball:b2BodyDef= new b2BodyDef();
			cannonball.position.Set(90/world_scale, 90/world_scale);
			cannonball.type=b2Body.b2_dynamicBody;
			var ball:b2CircleShape=new b2CircleShape(10/world_scale);
			var cannonball_fixture:b2FixtureDef = new b2FixtureDef();
			cannonball_fixture.shape=ball;
			cannonball_fixture.friction=0.9;
			cannonball_fixture.density=20;
			cannonball_fixture.restitution=0.5;
			var the_cannonball_itself:b2Body=world.CreateBody(cannonball);
			the_cannonball_itself.CreateFixture(cannonball_fixture);
		}
		public function the_wheel_motors():void {
			var front_wheel_joint:b2RevoluteJointDef = new b2RevoluteJointDef();
			front_wheel_joint.enableMotor=true;
			front_wheel_joint.Initialize(catapult_chassis_body, front_wheel_body,new b2Vec2(0,0));
			front_wheel_joint.localAnchorA=new b2Vec2(80/world_scale,0);
			front_wheel_joint.localAnchorB=new b2Vec2(0,0);
			front_wheel_revolute_joint=world.CreateJoint(front_wheel_joint) as b2RevoluteJoint;
			front_wheel_revolute_joint.SetMaxMotorTorque(1000000);
			//
			var rear_wheel_joint:b2RevoluteJointDef = new b2RevoluteJointDef();
			rear_wheel_joint.enableMotor=true;
			rear_wheel_joint.Initialize(catapult_chassis_body, rear_wheel_body,new b2Vec2(0,0));
			rear_wheel_joint.localAnchorA=new b2Vec2(-80/world_scale,0);
			rear_wheel_joint.localAnchorB=new b2Vec2(0,0);
			rear_wheel_revolute_joint=world.CreateJoint(rear_wheel_joint) as b2RevoluteJoint;
			rear_wheel_revolute_joint.SetMaxMotorTorque(1000000);
		}
		public function the_wheels():void {
			var rear_wheel:b2BodyDef= new b2BodyDef();
			rear_wheel.position.Set(250/world_scale, 200/world_scale);
			rear_wheel.type=b2Body.b2_dynamicBody;
			var rear_wheel_shape:b2CircleShape=new b2CircleShape(40/world_scale);
			var rear_wheel_fixture:b2FixtureDef = new b2FixtureDef();
			rear_wheel_fixture.shape=rear_wheel_shape;
			rear_wheel_fixture.friction=0.9;
			rear_wheel_fixture.density=30;
			rear_wheel_fixture.restitution=0.1;
			rear_wheel_body=world.CreateBody(rear_wheel);
			rear_wheel_body.CreateFixture(rear_wheel_fixture);
			//
			var front_wheel:b2BodyDef= new b2BodyDef();
			front_wheel.position.Set(450/world_scale, 200/world_scale);
			front_wheel.type=b2Body.b2_dynamicBody;
			var front_wheel_shape:b2CircleShape=new b2CircleShape(40/world_scale);
			var front_wheel_fixture:b2FixtureDef = new b2FixtureDef();
			front_wheel_fixture.shape=front_wheel_shape;
			front_wheel_fixture.friction=0.9;
			front_wheel_fixture.density=30;
			front_wheel_fixture.restitution=0.1;
			front_wheel_body=world.CreateBody(front_wheel);
			front_wheel_body.CreateFixture(front_wheel_fixture);
		}
		public function the_catapult_motor():void {
			var arm_joint:b2RevoluteJointDef = new b2RevoluteJointDef();
			arm_joint.enableMotor=true;
			arm_joint.enableLimit=true;
			arm_joint.Initialize(catapult_chassis_body, catapult_arm_body,new b2Vec2(0,0));
			arm_joint.localAnchorA=new b2Vec2(-80/world_scale,-90/world_scale);
			arm_joint.localAnchorB=new b2Vec2(60/world_scale,0);
			arm_revolute_joint=world.CreateJoint(arm_joint) as b2RevoluteJoint;
			arm_revolute_joint.SetMotorSpeed(1000);
			arm_revolute_joint.SetLimits(-Math.PI,Math.PI/3);
			arm_revolute_joint.SetMaxMotorTorque(1);
		}
		public function the_catapult_arm():void {
			var catapult_arm:b2BodyDef = new b2BodyDef();
			catapult_arm.allowSleep=false;
			catapult_arm.position.Set(210/world_scale,110/world_scale);
			catapult_arm.type=b2Body.b2_dynamicBody;
			var arm_part:b2PolygonShape = new b2PolygonShape();
			arm_part.SetAsOrientedBox(150/world_scale, 10/world_scale, new b2Vec2(0,0),0);
			var arm_part_fixture:b2FixtureDef = new b2FixtureDef();
			arm_part_fixture.shape=arm_part;
			arm_part_fixture.friction=0.9;
			arm_part_fixture.density=5;
			arm_part_fixture.restitution=0.1;
			var stopper:b2PolygonShape = new b2PolygonShape();
			stopper.SetAsOrientedBox(10/world_scale, 20/world_scale, new b2Vec2(-140/world_scale,-30/world_scale),0);
			var stopper_fixture:b2FixtureDef = new b2FixtureDef();
			stopper_fixture.shape=stopper;
			stopper_fixture.friction=0.9;
			stopper_fixture.density=10;
			stopper_fixture.restitution=0.1;
			catapult_arm_body=world.CreateBody(catapult_arm);
			catapult_arm_body.CreateFixture(arm_part_fixture);
			catapult_arm_body.CreateFixture(stopper_fixture);
		}
		public function the_catapult_body():void {
			var catapult_body:b2BodyDef = new b2BodyDef();
			catapult_body.position.Set(350/world_scale,200/world_scale);
			catapult_body.type=b2Body.b2_dynamicBody;
			var main_part:b2PolygonShape = new b2PolygonShape();
			main_part.SetAsOrientedBox(125/world_scale, 20/world_scale, new b2Vec2(0,0),0);
			var chassis_fixture:b2FixtureDef = new b2FixtureDef();
			chassis_fixture.shape=main_part;
			chassis_fixture.friction=0.9;
			chassis_fixture.density=50;
			chassis_fixture.restitution=0.1;
			var fixed_arm:b2PolygonShape = new b2PolygonShape();
			fixed_arm.SetAsOrientedBox(20/world_scale, 60/world_scale, new b2Vec2(-80/world_scale,-40/world_scale),0);
			var fixed_arm_fixture:b2FixtureDef = new b2FixtureDef();
			fixed_arm_fixture.shape=fixed_arm;
			fixed_arm_fixture.friction=0.9;
			fixed_arm_fixture.density=1;
			fixed_arm_fixture.restitution=0.1;
			catapult_chassis_body=world.CreateBody(catapult_body);
			catapult_chassis_body.CreateFixture(chassis_fixture);
			catapult_chassis_body.CreateFixture(fixed_arm_fixture);
		}
		public function the_ground():void {
			var ground:b2BodyDef= new b2BodyDef();
			ground.position.Set(250/world_scale, 400/world_scale);
			var my_box:b2PolygonShape = new b2PolygonShape();
			my_box.SetAsBox(1000/world_scale, 15/world_scale);
			var ground_fixture:b2FixtureDef = new b2FixtureDef();
			ground_fixture.shape=my_box;
			ground_fixture.friction=0.9;
			ground_fixture.restitution=0.1;
			var the_ground_itself:b2Body=world.CreateBody(ground);
			the_ground_itself.CreateFixture(ground_fixture);
		}
		public function key_up(event:KeyboardEvent):void {
			switch (event.keyCode) {
				case 39 :
					right_key_pressed=false;
					break;
				case 37 :
					left_key_pressed=false;
					break;
			}
		}
		public function key_down(event:KeyboardEvent):void {
			switch (event.keyCode) {
				case 39 :
					right_key_pressed=true;
					left_key_pressed=false;
					break;
				case 37 :
					left_key_pressed=true;
					right_key_pressed=false;
					break;
				case 32 :
					arm_revolute_joint.SetMaxMotorTorque(10000);
					break;
			}
		}
		public function debug_draw():void {
			var debug_draw:b2DebugDraw = new b2DebugDraw();
			var debug_sprite:Sprite = new Sprite();
			addChild(debug_sprite);
			debug_draw.SetSprite(debug_sprite);
			debug_draw.SetDrawScale(world_scale);
			debug_draw.SetFlags(b2DebugDraw.e_shapeBit|b2DebugDraw.e_jointBit);
			debug_draw.SetFillAlpha(0.5);
			world.SetDebugDraw(debug_draw);
		}
		public function set_motor_speed():void {
			var current_speed:Number;
			if (right_key_pressed) {
				current_speed=1;
			}
			if (left_key_pressed) {
				current_speed=-1;
			}
			if (! right_key_pressed&&! left_key_pressed) {
				current_speed=rear_wheel_revolute_joint.GetMotorSpeed()*0.9;
				if (Math.abs(current_speed)<0.1) {
					current_speed=0;
				}
			}
			rear_wheel_revolute_joint.SetMotorSpeed(current_speed);
			front_wheel_revolute_joint.SetMotorSpeed(current_speed);
		}
		public function update(e:Event):void {
			set_motor_speed();
			world.Step(1/30,10,10);
			world.ClearForces();
			world.DrawDebugData();
		}
	}
}

No need to download, just cut and paste on the first catapult prototype.

Next time, full comments and some other interesting features...

Get the most popular Phaser 3 book

Through 202 pages, 32 source code examples and an Android Studio project you will learn how to build cross platform HTML5 games and create a complete game along the way.

Get the book

214 GAME PROTOTYPES EXPLAINED WITH SOURCE CODE
// 1+2=3
// 100 rounds
// 10000000
// 2 Cars
// 2048
// A Blocky Christmas
// A Jumping Block
// A Life of Logic
// Angry Birds
// Angry Birds Space
// Artillery
// Astro-PANIC!
// Avoider
// Back to Square One
// Ball Game
// Ball vs Ball
// Ball: Revamped
// Balloon Invasion
// BallPusher
// Ballz
// Bar Balance
// Bejeweled
// Biggification
// Block it
// Blockage
// Bloons
// Boids
// Bombuzal
// Boom Dots
// Bouncing Ball
// Bouncing Ball 2
// Bouncy Light
// BoxHead
// Breakout
// Bricks
// Bubble Chaos
// Bubbles 2
// Card Game
// Castle Ramble
// Chronotron
// Circle Chain
// Circle Path
// Circle Race
// Circular endless runner
// Cirplosion
// CLOCKS - The Game
// Color Hit
// Color Jump
// ColorFill
// Columns
// Concentration
// Crossy Road
// Crush the Castle
// Cube Jump
// CubesOut
// Dash N Blast
// Dashy Panda
// Deflection
// Diamond Digger Saga
// Don't touch the spikes
// Dots
// Down The Mountain
// Drag and Match
// Draw Game
// Drop Wizard
// DROP'd
// Dudeski
// Dungeon Raid
// Educational Game
// Elasticity
// Endless Runner
// Erase Box
// Eskiv
// Farm Heroes Saga
// Filler
// Flappy Bird
// Fling
// Flipping Legend
// Floaty Light
// Fuse Ballz
// GearTaker
// Gem Sweeper
// Globe
// Goat Rider
// Gold Miner
// Grindstone
// GuessNext
// Helicopter
// Hero Emblems
// Hero Slide
// Hexagonal Tiles
// HookPod
// Hop Hop Hop Underwater
// Horizontal Endless Runner
// Hundreds
// Hungry Hero
// Hurry it's Christmas
// InkTd
// Iromeku
// Jet Set Willy
// Jigsaw Game
// Knife Hit
// Knightfall
// Legends of Runeterra
// Lep's World
// Line Rider
// Lumines
// Magick
// MagOrMin
// Mass Attack
// Math Game
// Maze
// Meeblings
// Memdot
// Metro Siberia Underground
// Mike Dangers
// Mikey Hooks
// Nano War
// Nodes
// o:anquan
// One Button Game
// One Tap RPG
// Ononmin
// Pacco
// Perfect Square!
// Perfectionism
// Phyballs
// Pixel Purge
// PixelField
// Planet Revenge
// Plants Vs Zombies
// Platform
// Platform game
// Plus+Plus
// Pocket Snap
// Poker
// Pool
// Pop the Lock
// Pop to Save
// Poux
// Pudi
// Pumpkin Story
// Puppet Bird
// Pyramids of Ra
// qomp
// Quick Switch
// Racing
// Radical
// Rebuild Chile
// Renju
// Rise Above
// Risky Road
// Roguelike
// Roly Poly
// Run Around
// Rush Hour
// SameGame
// SamePhysics
// Save the Totem
// Security
// Serious Scramblers
// Shrink it
// Sling
// Slingy
// Snowflakes
// Sokoban
// Space Checkers
// Space is Key
// Spellfall
// Spinny Gun
// Splitter
// Spring Ninja
// Sproing
// Stabilize!
// Stack
// Stick Hero
// String Avoider
// Stringy
// Sudoku
// Super Mario Bros
// Surfingers
// Survival Horror
// Talesworth Adventure
// Tetris
// The Impossible Line
// The Moops - Combos of Joy
// The Next Arrow
// Threes
// Tic Tac Toe
// Timberman
// Tiny Wings
// Tipsy Tower
// Toony
// Totem Destroyer
// Tower Defense
// Trick Shot
// Tunnelball
// Turn
// Turnellio
// TwinSpin
// vvvvvv
// Warp Shift
// Way of an Idea
// Whack a Creep
// Wheel of Fortune
// Where's my Water
// Wish Upon a Star
// Word Game
// Wordle
// Worms
// Yanga
// Yeah Bunny
// Zhed
// zNumbers