Two ways to make Box2D cars

核心提示：I am showing you two ways to make cars with Box2d, with source codes includedThese are examples I found on the web – I will make my ones later – you

I am showing you two ways to make cars with Box2d, with source codes included

These are examples I found on the web – I will make my ones later – you can find interesting in order to make cars using Box2D.

Top Down Car Simulation

Making a top down game in Box2D is not that different than making a side view game… you just don’t have to set gravity.

Here it is a top-down racing game

And this is the script to handle it

import　Box2D.Collision.*;//　bounding　box　of　our　world
import　Box2D.Common.Math.*;//　for　vector(define　gravity)
import　Box2D.Dynamics.*;//　define　bodies　and　define　world
import　Box2D.Dynamics.Joints.*;
import　Box2D.Collision.Shapes.*;//　define　our　shapes
import　flash.display.*;//　sprite　class
　
const　MAX_STEER_ANGLE:Number　=　Math.PI/3;
const　STEER_SPEED　=　1.5;
const　SIDEWAYS_FRICTION_FORCE:Number　=　10;
const　HORSEPOWERS:Number　=　40
const　CAR_STARTING_POS:b2Vec2　=　new　b2Vec2(10,10);
　
const　leftRearWheelPosition:b2Vec2　=　new　b2Vec2(-1.5,1.90);
const　rightRearWheelPosition:b2Vec2　=　new　b2Vec2(1.5,1.9);
const　leftFrontWheelPosition:b2Vec2　=　new　b2Vec2(-1.5,-1.9);
const　rightFrontWheelPosition:b2Vec2　=　new　b2Vec2(1.5,-1.9);
　
var　engineSpeed:Number　=0;
var　steeringAngle:Number　=　0
　
var　myWorld:b2World;
　
var　worldBox:b2AABB　=　new　b2AABB();
worldBox.lowerBound.Set(-100,-100);
worldBox.upperBound.Set(100,100);
　
myWorld　=　new　b2World(worldBox,　new　b2Vec2(0,0)　,　true);
　
//Create　some　static　stuff
var　staticDef　=　new　b2BodyDef();
staticDef.position.Set(5,20);
var　staticBox　=　new　b2PolygonDef();
staticBox.SetAsBox(5,5);
myWorld.CreateBody(staticDef).CreateShape(staticBox);
staticDef.position.x　=　25;
myWorld.CreateBody(staticDef).CreateShape(staticBox);
staticDef.position.Set(15,　24);
myWorld.CreateBody(staticDef).CreateShape(staticBox);
　
　
//　define　our　body
var　bodyDef:b2BodyDef　=　new　b2BodyDef();
bodyDef.linearDamping　=　1;
bodyDef.angularDamping　=　1;
bodyDef.position　=　CAR_STARTING_POS.Copy()
　
var　body:b2Body　=　myWorld.CreateBody(bodyDef);
body.SetMassFromShapes();
　
var　leftWheelDef:b2BodyDef　=　new　b2BodyDef();
leftWheelDef.position　=　CAR_STARTING_POS.Copy();
leftWheelDef.position.Add(leftFrontWheelPosition);
var　leftWheel:b2Body　=　myWorld.CreateBody(leftWheelDef);
　
var　rightWheelDef:b2BodyDef　=　new　b2BodyDef();
rightWheelDef.position　=　CAR_STARTING_POS.Copy();
rightWheelDef.position.Add(rightFrontWheelPosition);
var　rightWheel:b2Body　=　myWorld.CreateBody(rightWheelDef);
　
var　leftRearWheelDef:b2BodyDef　=　new　b2BodyDef();
leftRearWheelDef.position　=　CAR_STARTING_POS.Copy();
leftRearWheelDef.position.Add(leftRearWheelPosition);
var　leftRearWheel:b2Body　=　myWorld.CreateBody(leftRearWheelDef);
　
var　rightRearWheelDef:b2BodyDef　=　new　b2BodyDef();
rightRearWheelDef.position　=　CAR_STARTING_POS.Copy();
rightRearWheelDef.position.Add(rightRearWheelPosition);
var　rightRearWheel:b2Body　=　myWorld.CreateBody(rightRearWheelDef);
　
//　define　our　shapes
var　boxDef:b2PolygonDef　=　new　b2PolygonDef();
boxDef.SetAsBox(1.5,2.5);
boxDef.density　=　1;
body.CreateShape(boxDef);
　
//Left　Wheel　shape
var　leftWheelShapeDef　=　new　b2PolygonDef();
leftWheelShapeDef.SetAsBox(0.2,0.5);
leftWheelShapeDef.density　=　1;
leftWheel.CreateShape(leftWheelShapeDef);
　
//Right　Wheel　shape
var　rightWheelShapeDef　=　new　b2PolygonDef();
rightWheelShapeDef.SetAsBox(0.2,0.5);
rightWheelShapeDef.density　=　1;
rightWheel.CreateShape(rightWheelShapeDef);
　
//Left　Wheel　shape
var　leftRearWheelShapeDef　=　new　b2PolygonDef();
leftRearWheelShapeDef.SetAsBox(0.2,0.5);
leftRearWheelShapeDef.density　=　1;
leftRearWheel.CreateShape(leftRearWheelShapeDef);
　
//Right　Wheel　shape
var　rightRearWheelShapeDef　=　new　b2PolygonDef();
rightRearWheelShapeDef.SetAsBox(0.2,0.5);
rightRearWheelShapeDef.density　=　1;
rightRearWheel.CreateShape(rightRearWheelShapeDef);
　
body.SetMassFromShapes();
leftWheel.SetMassFromShapes();
rightWheel.SetMassFromShapes();
leftRearWheel.SetMassFromShapes();
rightRearWheel.SetMassFromShapes();
　
var　leftJointDef:b2RevoluteJointDef　=　new　b2RevoluteJointDef();
leftJointDef.Initialize(body,　leftWheel,　leftWheel.GetWorldCenter());
leftJointDef.enableMotor　=　true;
leftJointDef.maxMotorTorque　=　100;
　
var　rightJointDef　=　new　b2RevoluteJointDef();
rightJointDef.Initialize(body,　rightWheel,　rightWheel.GetWorldCenter());
rightJointDef.enableMotor　=　true;
rightJointDef.maxMotorTorque　=　100;
　
var　leftJoint:b2RevoluteJoint　=　b2RevoluteJoint(myWorld.CreateJoint(leftJointDef));
var　rightJoint:b2RevoluteJoint　=　b2RevoluteJoint(myWorld.CreateJoint(rightJointDef));
　
var　leftRearJointDef:b2PrismaticJointDef　=　new　b2PrismaticJointDef();
leftRearJointDef.Initialize(body,　leftRearWheel,　leftRearWheel.GetWorldCenter(),　new　b2Vec2(1,0));
leftRearJointDef.enableLimit　=　true;
leftRearJointDef.lowerTranslation　=　leftRearJointDef.upperTranslation　=　0;
　
var　rightRearJointDef:b2PrismaticJointDef　=　new　b2PrismaticJointDef();
rightRearJointDef.Initialize(body,　rightRearWheel,　rightRearWheel.GetWorldCenter(),　new　b2Vec2(1,0));
rightRearJointDef.enableLimit　=　true;
rightRearJointDef.lowerTranslation　=　rightRearJointDef.upperTranslation　=　0;
　
myWorld.CreateJoint(leftRearJointDef);
myWorld.CreateJoint(rightRearJointDef);
　
　
//　debug　draw
var　dbgDraw:b2DebugDraw　=　new　b2DebugDraw();
dbgDraw.m_sprite　=　new　Sprite();
addChild(dbgDraw.m_sprite);
dbgDraw.m_drawScale　=　20.0;
dbgDraw.m_fillAlpha　=　0.3;
dbgDraw.m_lineThickness　=　1.0;
dbgDraw.m_drawFlags　=　b2DebugDraw.e_shapeBit　|b2DebugDraw.e_centerOfMassBit;
myWorld.SetDebugDraw(dbgDraw);
　
　
//==========　FUNCTIONS　==========
　
//This　function　applies　a　"friction"　in　a　direction　orthogonal　to　the　body's　axis.
function　killOrthogonalVelocity(targetBody:b2Body){
　var　localPoint　=　new　b2Vec2(0,0);
　var　velocity:b2Vec2　=　targetBody.GetLinearVelocityFromLocalPoint(localPoint);
　
　var　sidewaysAxis　=　targetBody.GetXForm().R.col2.Copy();
　sidewaysAxis.Multiply(b2Math.b2Dot(velocity,sidewaysAxis))
　
　targetBody.SetLinearVelocity(sidewaysAxis);//targetBody.GetWorldPoint(localPoint));
}
　
stage.addEventListener(KeyboardEvent.KEY_DOWN,　keyPressed_handler);
stage.addEventListener(KeyboardEvent.KEY_UP,　keyReleased_handler);
　
function　keyPressed_handler(e:KeyboardEvent)　{
　if(e.keyCode　==　Keyboard.UP){
　　body.WakeUp();
　　engineSpeed　=　-HORSEPOWERS;
　}
　if(e.keyCode　==　Keyboard.DOWN){
　　engineSpeed　=　HORSEPOWERS;
　}
　if(e.keyCode　==　Keyboard.RIGHT){
　　steeringAngle　=　MAX_STEER_ANGLE
　}
　if(e.keyCode　==　Keyboard.LEFT){
　　steeringAngle　=　-MAX_STEER_ANGLE
　}
}
　
function　keyReleased_handler(e:KeyboardEvent){
　if(e.keyCode　==　Keyboard.UP　||　e.keyCode　==　Keyboard.DOWN){
　　engineSpeed　=　0;
　}　
　if(e.keyCode　==　Keyboard.LEFT　||　e.keyCode　==　Keyboard.RIGHT){
　　steeringAngle　=　0;
　}
}
　
addEventListener(Event.ENTER_FRAME,　Update,　false,　0　,　true);
　
function　Update(e:Event):void　{
　myWorld.Step(1/30,　8);
　killOrthogonalVelocity(leftWheel);
　killOrthogonalVelocity(rightWheel);
　killOrthogonalVelocity(leftRearWheel);
　killOrthogonalVelocity(rightRearWheel);
　
　//Driving
　var　ldirection　=　leftWheel.GetXForm().R.col2.Copy();
　ldirection.Multiply(engineSpeed);
　var　rdirection　=　rightWheel.GetXForm().R.col2.Copy()
　rdirection.Multiply(engineSpeed);
　leftWheel.ApplyForce(ldirection,　leftWheel.GetPosition());
　rightWheel.ApplyForce(rdirection,　rightWheel.GetPosition());
　
　//Steering
　var　mspeed:Number;
　mspeed　=　steeringAngle　-　leftJoint.GetJointAngle();
　leftJoint.SetMotorSpeed(mspeed　*　STEER_SPEED);
　mspeed　=　steeringAngle　-　rightJoint.GetJointAngle();
　rightJoint.SetMotorSpeed(mspeed　*　STEER_SPEED);
}