转载自：http://gym202.blog.163.com/blog/static/95543274201011765141871/
demo : http://www.emanueleferonato.com/downloads/box2dplat3.swf
demo控制 左右键是左右移动 上方向键是起跳
下面是源码 ：
box2d是的角色邹形 能跳 能移动 能发射东西
/*
知识补漏：
world其本质也是个body, 即所有b2Body对象的parent 。CreateBody() 等一些Create ， Create就相当于flash player里的 add ， CreateBody() CreateShape（） 就相当于flash player里的 addChild()
ground_sensor.SetAsOrientedBox(10/pixels_in_a_meter,5/pixels_in_a_meter,new b2Vec2(0,27/pixels_in_a_meter), 0);
后面的坐标new b2Vec2(0,27/pixels_in_a_meter)其原点是body的中心（即以body的中心为原点），而不是以world中的原点为原点，
（总结：以body的中心为原点,向右向下为xy轴的正方向）
GetWorldCenter得到是整个body的中心,GetLocalCenter得到是SetAsBox() 这个组成的对象的中心
下面增加了b2ContactListene类进行了侦听 ，并对其进行了重写..
*/
package {
import flash.display.Sprite;
import flash.events.Event;
import Box2D.Dynamics.*;
import Box2D.Collision.*;
import Box2D.Collision.Shapes.*;
import Box2D.Common.Math.*;
import General.Input;
import flash.events.MouseEvent;
public class HelloWorld extends Sprite {
public var m_world:b2World;
public var pixels_in_a_meter:int=30;
public var bodyDef:b2BodyDef;
public var boxDef:b2PolygonDef;
public var m_input:Input;
public var xspeed:int=0;
public var bazooka:zooka=new zooka();
public var bazooka_angle:Number;
public var m_contactListener=new b2ContactListener();
var body:b2Body;
public function HelloWorld() {
addEventListener(Event.ENTER_FRAME, Update, false, 0, true);
var worldAABB:b2AABB = new b2AABB();
worldAABB.lowerBound.Set(-100.0, -100.0);
worldAABB.upperBound.Set(100.0, 100.0);
var gravity:b2Vec2=new b2Vec2(0.0,10.0);
var doSleep:Boolean=true;
m_world=new b2World(worldAABB,gravity,doSleep);
var m_sprite:Sprite;
m_sprite = new Sprite();
addChild(m_sprite);
var dbgDraw:b2DebugDraw = new b2DebugDraw();
var dbgSprite:Sprite = new Sprite();
m_sprite.addChild(dbgSprite);
dbgDraw.m_sprite=m_sprite;
dbgDraw.m_drawScale=30;
dbgDraw.m_alpha=1;
dbgDraw.m_fillAlpha=0.5;
dbgDraw.m_lineThickness=1;
dbgDraw.m_drawFlags=b2DebugDraw.e_shapeBit;
m_world.SetDebugDraw(dbgDraw);
var bodyDef:b2BodyDef;
var boxDef:b2PolygonDef;
var circleDef:b2CircleDef;
square_tile(250,395,500,10);
hero(100,370,20,40);
//
// adding the contact listener
m_world.SetContactListener(m_contactListener);
//
// Box2D input class - why should I bother making my one?
m_sprite = new Sprite();
addChild(m_sprite);
// input
m_input=new Input(m_sprite);
addChild(bazooka);
stage.addEventListener(MouseEvent.CLICK, shoot);
}
public function shoot(event:Event) {
bodyDef = new b2BodyDef();
bodyDef.position.Set((bazooka.x+(bazooka.width+3)*Math.cos(bazooka_angle))/pixels_in_a_meter, (bazooka.y+(bazooka.width+3)*Math.sin(bazooka_angle))/pixels_in_a_meter);
boxDef = new b2PolygonDef();
boxDef.SetAsBox(10/pixels_in_a_meter,10/pixels_in_a_meter);
boxDef.friction=0.3;
boxDef.density=1;
body=m_world.CreateBody(bodyDef);
body.CreateShape(boxDef);
body.SetMassFromShapes();
body.ApplyImpulse(new b2Vec2(Math.cos(bazooka_angle)*4, Math.sin(bazooka_angle)*4),body.GetWorldCenter());
}
public function square_tile(px:int,py:int,w:int,h:int) {
bodyDef = new b2BodyDef();
bodyDef.position.Set(px/pixels_in_a_meter, py/pixels_in_a_meter);
boxDef = new b2PolygonDef();
boxDef.SetAsBox(real_pixels(w), real_pixels(h));
boxDef.friction=0.3;
boxDef.density=0;
body=m_world.CreateBody(bodyDef);
body.CreateShape(boxDef);
body.SetMassFromShapes();
}
public function hero(px:int, py:int, w:int, h:int) {
bodyDef = new b2BodyDef();
bodyDef.position.Set(px/pixels_in_a_meter, py/pixels_in_a_meter);
boxDef = new b2PolygonDef();
boxDef.SetAsBox(real_pixels(w), real_pixels(h));
boxDef.density=1.0;
boxDef.friction=0.3;
boxDef.restitution=0.2;
bodyDef.userData = new Sprite();
bodyDef.userData.name="Player";
body=m_world.CreateBody(bodyDef);
body.SetBullet(true);
body.CreateShape(boxDef);
//
var ground_sensor:b2PolygonDef = new b2PolygonDef();
ground_sensor.isSensor=true;
ground_sensor.userData="groundsensor";
ground_sensor.SetAsOrientedBox(10/pixels_in_a_meter,5/pixels_in_a_meter,new b2Vec2(0,27/pixels_in_a_meter), 0);//后面的坐标new b2Vec2(0,27/pixels_in_a_meter)其原点是body的中心（即以body的中心为原点），而不是以world中的原点为原点，（总结：以body的中心为原点,向右向下为xy轴的正方向）
body.CreateShape(ground_sensor);
//
body.SetMassFromShapes();
}
public function real_pixels(n:int) {
return (n/pixels_in_a_meter/2);
}
public function Update(e:Event):void {
m_world.Step(1/30, 10);
xspeed=0;
for (var bb:b2Body = m_world.m_bodyList; bb; bb = bb.m_next) {
if (bb.GetUserData()!=null) {
if (Input.isKeyDown(39)) { // right arrow
xspeed=3;
} else if (Input.isKeyDown(37)) { // left arrow
xspeed=-3;
}
if (Input.isKeyDown(38)) {// up arrow
if (m_contactListener.can_jump()) { // checking if the hero can jump
bb.ApplyImpulse(new b2Vec2(0.0, -1.0), bb.GetWorldCenter());//这里用bb.GetWorldCenter(),而不用bb.GetLocalCenter()因为用GetLocalCenter容易引起bug
}
}
if (xspeed) {
bb.WakeUp();
bb.m_linearVelocity.x=xspeed;
}
bb.m_sweep.a=0;
bazooka.x=bb.m_userData.x=bb.GetPosition().x*30;
bazooka.y=bb.m_userData.y=bb.GetPosition().y*30;
var dist_x=bazooka.x-mouseX;
var dist_y=bazooka.y-mouseY;
bazooka_angle=Math.atan2(- dist_y,- dist_x);
bazooka.rotation=bazooka_angle*57.2957795;
}
}
Input.update();
}
}
}
b2ContactListener类的重写：
/*
* Copyright (c) 2006-2007 Erin Catto http://www.gphysics.com
*
* This software is provided 'as-is', without any express or implied
* warranty. In no event will the authors be held liable for any damages
* arising from the use of this software.
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
* 2. Altered source versions must be plainly marked as such, and must not be
* misrepresented as being the original software.
* 3. This notice may not be removed or altered from any source distribution.
*/
package Box2D.Dynamics{
import Box2D.Collision.*;
import Box2D.Collision.Shapes.*;
import Box2D.Dynamics.Contacts.*;
import Box2D.Dynamics.*;
import Box2D.Common.Math.*;
import Box2D.Common.*;
/// Implement this class to get collision results. You can use these results for
/// things like sounds and game logic. You can also get contact results by
/// traversing the contact lists after the time step. However, you might miss
/// some contacts because continuous physics leads to sub-stepping.
/// Additionally you may receive multiple callbacks for the same contact in a
/// single time step.
/// You should strive to make your callbacks efficient because there may be
/// many callbacks per time step.
/// @warning The contact separation is the last computed value.
/// @warning You cannot create/destroy Box2D entities inside these callbacks.
public class b2ContactListener {
var canjump:Boolean=false;
/// Called when a contact point is added. This includes the geometry
/// and the forces.
public function can_jump() {
return (canjump);
}
public virtual function Add(point:b2ContactPoint):void {}
/// Called when a contact point persists. This includes the geometry
/// and the forces.
//点持续接触时
public virtual function Persist(point:b2ContactPoint):void {
if (point.shape1.GetUserData()=="groundsensor"||point.shape2.GetUserData()=="groundsensor") {
canjump=true;
}
}
/// Called when a contact point is removed. This includes the last
/// computed geometry and forces.
public virtual function Remove(point:b2ContactPoint):void {
if (point.shape1.GetUserData()=="groundsensor"||point.shape2.GetUserData()=="groundsensor") {
canjump=false;
}
}
/// Called after a contact point is solved.
public virtual function Result(point:b2ContactResult):void {
}
}
}