物理模拟引擎box2D-1
几个常用的概念
rigid body
shape
constraint
contact constraint
joint
joint limit
joint motor
world
Hello Box2D
Creating a World
Caution
The world AABB should always be bigger then the region where your bodies are located. It is better to make the world AABB too big than too small. If a body reaches the boundary of the world AABB it will be frozen and will stop simulating.
and b2 allow object to sleep.
now we create world object.
we can following the steps as
Creating a World--Creating a Ground Box--Creating a Dynamic Body--
Simulating the World (of Box2D). the following is source code and the attacted is flash.
rigid body
shape
constraint
contact constraint
joint
joint limit
joint motor
world
Hello Box2D
Creating a World
var worldAABB:b2AABB = new b2AABB(); worldAABB.lowerBound.Set(-100.0, -100.0); worldAABB.upperBound.Set(100.0, 100.0);
Caution
The world AABB should always be bigger then the region where your bodies are located. It is better to make the world AABB too big than too small. If a body reaches the boundary of the world AABB it will be frozen and will stop simulating.
and b2 allow object to sleep.
var gravity:b2Vec2 = new b2Vec2 (0.0, -10.0); var doSleep:Boolean = true;
now we create world object.
var world:b2World = new b2World(worldAABB, gravity, doSleep);
we can following the steps as
Creating a World--Creating a Ground Box--Creating a Dynamic Body--
Simulating the World (of Box2D). the following is source code and the attacted is flash.
package{
import flash.display.Sprite;
import flash.events.Event;
// Classes used in this example
import Box2D.Dynamics.*;
import Box2D.Collision.*;
import Box2D.Collision.Shapes.*;
import Box2D.Common.Math.*;
[SWF(width="640", height="360", backgroundColor="#000000", frameRate="30")]
public class HelloWorld extends Sprite{
[Embed(source='assets/PhysBox.swf')]
public var PhysBox:Class;
//public var FGmc:MovieClip = new FG as MovieClip;
[Embed(source='assets/PhysCircle.swf')]
public var PhysCircle:Class;
[Embed(source='assets/PhysGround.swf')]
public var PhysGround:Class;
public function HelloWorld(){
// Add event for main loop
addEventListener(Event.ENTER_FRAME, Update, false, 0, true);
// Creat world AABB
var worldAABB:b2AABB = new b2AABB();
worldAABB.lowerBound.Set(-100.0, -100.0);
worldAABB.upperBound.Set(100.0, 100.0);
// Define the gravity vector
var gravity:b2Vec2 = new b2Vec2(0.0, 10.0);
// Allow bodies to sleep
var doSleep:Boolean = true;
// Construct a world object
m_world = new b2World(worldAABB, gravity, doSleep);
// set debug draw
/*var dbgDraw:b2DebugDraw = new b2DebugDraw();
var dbgSprite:Sprite = new Sprite();
addChild(dbgSprite);
dbgDraw.m_sprite = dbgSprite;
dbgDraw.m_drawScale = 30.0;
dbgDraw.m_fillAlpha = 0.0;
dbgDraw.m_lineThickness = 1.0;
dbgDraw.m_drawFlags = 0xFFFFFFFF;
m_world.SetDebugDraw(dbgDraw);*/
// Vars used to create bodies
var body:b2Body;
var bodyDef:b2BodyDef;
var boxDef:b2PolygonDef;
var circleDef:b2CircleDef;
// Add ground body
bodyDef = new b2BodyDef();
//bodyDef.position.Set(15, 19);
bodyDef.position.Set(10, 12);
//bodyDef.angle = 0.1;
boxDef = new b2PolygonDef();
boxDef.SetAsBox(30, 3);
boxDef.friction = 0.3;
boxDef.density = 0; // static bodies require zero density
/*circleDef = new b2CircleDef();
circleDef.radius = 10;
circleDef.restitution = 0.2*/
// Add sprite to body userData
bodyDef.userData = new PhysGround();
//bodyDef.userData = new PhysCircle();
bodyDef.userData.width = 30 * 2 * 30;
bodyDef.userData.height = 30 * 2 * 3;
addChild(bodyDef.userData);
body = m_world.CreateBody(bodyDef);
body.CreateShape(boxDef);
//body.CreateShape(circleDef);
body.SetMassFromShapes();
// Add some objects
for (var i:int = 1; i < 10; i++){
bodyDef = new b2BodyDef();
bodyDef.position.x = Math.random() * 15 + 5;
bodyDef.position.y = Math.random() * 10;
var rX:Number = Math.random() + 0.5;
var rY:Number = Math.random() + 0.5;
// Box
if (Math.random() < 0.5){
boxDef = new b2PolygonDef();
boxDef.SetAsBox(rX, rY);
boxDef.density = 1.0;
boxDef.friction = 0.5;
boxDef.restitution = 0.2;
bodyDef.userData = new PhysBox();
bodyDef.userData.width = rX * 2 * 30;
bodyDef.userData.height = rY * 2 * 30;
body = m_world.CreateBody(bodyDef);
body.CreateShape(boxDef);
}
// Circle
else {
circleDef = new b2CircleDef();
circleDef.radius = rX;
circleDef.density = 1.0;
circleDef.friction = 0.5;
circleDef.restitution = 0.2
bodyDef.userData = new PhysCircle();
bodyDef.userData.width = rX * 2 * 30;
bodyDef.userData.height = rX * 2 * 30;
body = m_world.CreateBody(bodyDef);
body.CreateShape(circleDef);
}
body.SetMassFromShapes();
addChild(bodyDef.userData);
}
}
public function Update(e:Event):void{
m_world.Step(m_timeStep, m_iterations);
// Go through body list and update sprite positions/rotations
for (var bb:b2Body = m_world.m_bodyList; bb; bb = bb.m_next){
if (bb.m_userData is Sprite){
bb.m_userData.x = bb.GetPosition().x * 30;
bb.m_userData.y = bb.GetPosition().y * 30;
bb.m_userData.rotation = bb.GetAngle() * (180/Math.PI);
}
}
}
public var m_world:b2World;
public var m_iterations:int = 10;
public var m_timeStep:Number = 1.0/30.0;
}
}