用Box2D创建真正的爆炸—爆炸的物体以及用鼠标指定爆炸的中心

      之前我发表了题为怎样使用Box2D来创建真正的爆炸的文章，然后我收到了很多的提问，其中大部分问到怎样实现在单击物体的时候发生爆炸，并且用鼠标指针设定爆炸的中心。
   所以我稍微改了一点脚本，现在你已经可以实现这样的功能了，并且为了保持速度，我移除了所有的形状很小的物体。它们只会减慢原型的速度，而没有任何的好处。

所以这就是你要的了：
   [flash]http://www.emanueleferonato.com/wp-content/uploads/2012/01/boom.swf[/flash]
   单击任何一个对象（静态的或者是动态的），就可以让它爆炸了。

   下面是没有注释的，并且还将要进行优化的代码：

package {
import Box2D.Dynamics.*;
import Box2D.Collision.*;
import Box2D.Collision.Shapes.*;
import Box2D.Common.Math.*;
import flash.display.Sprite;
import flash.events.MouseEvent;
import flash.events.Event;
public class Main extends Sprite {
private var world:b2World=new b2World(new b2Vec2(0,10),true);
private var worldScale:int=30;
private var laserSegment:b2Segment;
private var drawing:Boolean=false;
private var affectedByLaser:Vector.<b2Body>;
private var entryPoint:Vector.<b2Vec2>;
private var explodingBodies:Vector.<b2Body>;
private var explosionCenterX:Number;
private var explosionCenterY:Number;
private var chunks:Number=5;
private var explosionRadius:Number=50;
public function Main() {
debugDraw();
addWall(320,480,640,20);
addWall(320,0,640,20);
addWall(0,240,20,480);
addWall(640,240,20,480);
addWall(320,240,200,200);
addWall(250,110,60,60);
addWall(390,110,60,60);
addEventListener(Event.ENTER_FRAME, updateWorld);
stage.addEventListener(MouseEvent.MOUSE_DOWN,mousePressed);
}
private function mousePressed(e:MouseEvent):void {
var cutAngle:Number;
explosionCenterX=mouseX;
explosionCenterY=mouseY;
var clickedBody:b2Body=GetBodyAtXY(new b2Vec2(explosionCenterX/worldScale,explosionCenterY/worldScale));
explodingBodies=new Vector.<b2Body>();
if (clickedBody!=null) {
explodingBodies.push(clickedBody);
for (var i:Number=0; i<chunks; i++) {
cutAngle=Math.random()*Math.PI*2;
laserSegment=new b2Segment();
laserSegment.p1=new b2Vec2((explosionCenterX+i/10-200*Math.cos(cutAngle))/worldScale,(explosionCenterY-200*Math.sin(cutAngle))/worldScale);
laserSegment.p2=new b2Vec2((explosionCenterX+200*Math.cos(cutAngle))/worldScale,(explosionCenterY+200*Math.sin(cutAngle))/worldScale);
affectedByLaser=new Vector.<b2Body>();
entryPoint=new Vector.<b2Vec2>();
world.RayCast(laserFired,laserSegment.p1,laserSegment.p2);
world.RayCast(laserFired,laserSegment.p2,laserSegment.p1);
}
}
}
private function debugDraw():void {
var debugDraw:b2DebugDraw = new b2DebugDraw();
var debugSprite:Sprite = new Sprite();
addChild(debugSprite);
debugDraw.SetSprite(debugSprite);
debugDraw.SetDrawScale(worldScale);
debugDraw.SetFlags(b2DebugDraw.e_shapeBit|b2DebugDraw.e_jointBit);
debugDraw.SetFillAlpha(0.5);
world.SetDebugDraw(debugDraw);
}
private function addWall(pX:Number,pY:Number,w:Number,h:Number):void {
var wallShape:b2PolygonShape = new b2PolygonShape();
wallShape.SetAsBox(w/worldScale/2,h/worldScale/2);
var wallFixture:b2FixtureDef = new b2FixtureDef();
wallFixture.density=0;
wallFixture.friction=1;
wallFixture.restitution=0.5;
wallFixture.shape=wallShape;
var wallBodyDef:b2BodyDef = new b2BodyDef();
wallBodyDef.position.Set(pX/worldScale,pY/worldScale);
var wall:b2Body=world.CreateBody(wallBodyDef);
wall.CreateFixture(wallFixture);
}
private function updateWorld(e:Event):void {
world.Step(1/30,10,10);
world.ClearForces();
world.DrawDebugData();
}
private function laserFired(fixture:b2Fixture,point:b2Vec2,normal:b2Vec2,fraction:Number):Number {
var affectedBody:b2Body=fixture.GetBody();
if (explodingBodies.indexOf(affectedBody)!=-1) {
var affectedPolygon:b2PolygonShape=fixture.GetShape() as b2PolygonShape;
var fixtureIndex:int=affectedByLaser.indexOf(affectedBody);
if (fixtureIndex==-1) {
affectedByLaser.push(affectedBody);
entryPoint.push(point);
}
else {
var rayCenter:b2Vec2=new b2Vec2((point.x+entryPoint[fixtureIndex].x)/2,(point.y+entryPoint[fixtureIndex].y)/2);
var rayAngle:Number=Math.atan2(entryPoint[fixtureIndex].y-point.y,entryPoint[fixtureIndex].x-point.x);
var polyVertices:Vector.<b2Vec2>=affectedPolygon.GetVertices();
var newPolyVertices1:Vector.<b2Vec2>=new Vector.<b2Vec2>();
var newPolyVertices2:Vector.<b2Vec2>=new Vector.<b2Vec2>();
var currentPoly:int=0;
var cutPlaced1:Boolean=false;
var cutPlaced2:Boolean=false;
for (var i:int=0; i<polyVertices.length; i++) {
var worldPoint:b2Vec2=affectedBody.GetWorldPoint(polyVertices[i]);
var cutAngle:Number=Math.atan2(worldPoint.y-rayCenter.y,worldPoint.x-rayCenter.x)-rayAngle;
if (cutAngle<Math.PI*-1) {
cutAngle+=2*Math.PI;
}
if (cutAngle>0&&cutAngle<=Math.PI) {
if (currentPoly==2) {
cutPlaced1=true;
newPolyVertices1.push(point);
newPolyVertices1.push(entryPoint[fixtureIndex]);
}
newPolyVertices1.push(worldPoint);
currentPoly=1;
}
else {
if (currentPoly==1) {
cutPlaced2=true;
newPolyVertices2.push(entryPoint[fixtureIndex]);
newPolyVertices2.push(point);
}
newPolyVertices2.push(worldPoint);
currentPoly=2;
}
}
if (! cutPlaced1) {
newPolyVertices1.push(point);
newPolyVertices1.push(entryPoint[fixtureIndex]);
}
if (! cutPlaced2) {
newPolyVertices2.push(entryPoint[fixtureIndex]);
newPolyVertices2.push(point);
}
createSlice(newPolyVertices1,newPolyVertices1.length);
createSlice(newPolyVertices2,newPolyVertices2.length);
world.DestroyBody(affectedBody);
}
}
return 1;
}
private function findCentroid(vs:Vector.<b2Vec2>, count:uint):b2Vec2 {
var c:b2Vec2 = new b2Vec2();
var area:Number=0.0;
var p1X:Number=0.0;
var p1Y:Number=0.0;
var inv3:Number=1.0/3.0;
for (var i:int = 0; i < count; ++i) {
var p2:b2Vec2=vs[i];
var p3:b2Vec2=i+1<count?vs[int(i+1)]:vs[0];
var e1X:Number=p2.x-p1X;
var e1Y:Number=p2.y-p1Y;
var e2X:Number=p3.x-p1X;
var e2Y:Number=p3.y-p1Y;
var D:Number = (e1X * e2Y - e1Y * e2X);
var triangleArea:Number=0.5*D;
area+=triangleArea;
c.x += triangleArea * inv3 * (p1X + p2.x + p3.x);
c.y += triangleArea * inv3 * (p1Y + p2.y + p3.y);
}
c.x*=1.0/area;
c.y*=1.0/area;
return c;
}
private function getArea(vs:Vector.<b2Vec2>, count:uint):Number {
var area:Number=0.0;
var p1X:Number=0.0;
var p1Y:Number=0.0;
var inv3:Number=1.0/3.0;
for (var i:int = 0; i < count; ++i) {
var p2:b2Vec2=vs[i];
var p3:b2Vec2=i+1<count?vs[int(i+1)]:vs[0];
var e1X:Number=p2.x-p1X;
var e1Y:Number=p2.y-p1Y;
var e2X:Number=p3.x-p1X;
var e2Y:Number=p3.y-p1Y;
var D:Number = (e1X * e2Y - e1Y * e2X);
var triangleArea:Number=0.5*D;
area+=triangleArea;
}
return area;
}
private function createSlice(vertices:Vector.<b2Vec2>,numVertices:int):void {
if (getArea(vertices,vertices.length)>=0.05) {
var centre:b2Vec2=findCentroid(vertices,vertices.length);
for (var i:int=0; i<numVertices; i++) {
vertices[i].Subtract(centre);
}
var sliceBody:b2BodyDef= new b2BodyDef();
sliceBody.position.Set(centre.x, centre.y);
sliceBody.type=b2Body.b2_dynamicBody;
var slicePoly:b2PolygonShape = new b2PolygonShape();
slicePoly.SetAsVector(vertices,numVertices);
var sliceFixture:b2FixtureDef = new b2FixtureDef();
sliceFixture.shape=slicePoly;
sliceFixture.density=1;
var worldSlice:b2Body=world.CreateBody(sliceBody);
worldSlice.CreateFixture(sliceFixture);
for (i=0; i<numVertices; i++) {
vertices[i].Add(centre);
}
var distX:Number=(centre.x*worldScale-explosionCenterX);
if (distX<0) {
if (distX<-explosionRadius) {
distX=0;
}
else {
distX=-50-distX;
}
}
else {
if (distX>explosionRadius) {
distX=0;
}
else {
distX=50-distX;
}
}
var distY:Number=(centre.y*worldScale-explosionCenterY);
if (distY<0) {
if (distY<-explosionRadius) {
distY=0;
}
else {
distY=-50-distY;
}
}
else {
if (distY>explosionRadius) {
distY=0;
}
else {
distY=50-distY;
}
}
distX*=0.25;
distY*=0.25;
worldSlice.SetLinearVelocity(new b2Vec2(distX,distY));
explodingBodies.push(worldSlice);
}
}
private function GetBodyAtXY(coordinate:b2Vec2):b2Body {
var touchedBody:b2Body=null;
world.QueryPoint(GetBodyCallback,coordinate);
function GetBodyCallback(fixture:b2Fixture):Boolean {
var shape:b2Shape=fixture.GetShape();
var inside:Boolean=shape.TestPoint(fixture.GetBody().GetTransform(),coordinate);
if (inside) {
touchedBody=fixture.GetBody();
return false;
}
return true;
}
return touchedBody;
}
}
}

复制代码

一旦我完成了最后一步：给爆炸添加纹理，我将会发上完整的教程。如果你想试试这个类，你可以复制/粘贴代码到你的例子中，例子可以在这里下载:使用Box2D来实现对象的分片，爆炸以及切割。