flash 切割游戏

flash 切割游戏
引用：http://bbs.9ria.com/thread-114856-1-1.html

Box2D切割引擎，这个引擎是从Box2D爆炸引擎演化而来的。

现在就要使用相同的思想以最真实的方式来切割刚体。

这是我做的效果：

在舞台上点击鼠标，会有一个小球以随机的速度从边上射出，看看它是怎么切割这块木桩的。我使用了“bullet time”来做这个东西，所以你可以看看它是怎么工作的，并且由于当这个小球以高速度飞行的时候，我有的时候会遇到一些问题，但是现在这里只是一个原型。

不管怎样，它是按下面的方式运行的：

当小球触碰到木桩的时候，我自定义的接触监听器对它进行了监听；

这时，我知道小球的位置和速度。假设小球可以切断这块木桩，通过小球的位置以及方向，我可以确定一条切割线；

将切割线应用到木桩上面，将它切成两半；

最后我将这个小球克隆，创建另外一个新的小球，这个小球与原来的小球有相同的速度和方向，这个小球将会和木桩相碰，用来展现小球和木桩碎片相碰撞的效果。

基本上就是这样了。

我将所有带有注释的源码贴出来：
package {

      import flash.display.Sprite;

      import flash.events.Event;

      import flash.events.MouseEvent;

      import flash.geom.Matrix;

      import flash.display.BitmapData;

      import Box2D.Dynamics.*;

      import Box2D.Collision.*;

      import Box2D.Collision.Shapes.*;

      import Box2D.Common.Math.*;

      public class Main extends Sprite {

            private var world:b2World=new b2World(new b2Vec2(0,10),true);

            // You can see the reason for creating the enterPointsVec in the coments in the intersection() method.

            private var enterPointsVec:Vector.<b2Vec2> = new Vector.<b2Vec2>();

            private var numEnterPoints:int=0;

            private var worldScale:Number=30;

            // custom contact listener

            private var customContact=new CustomContactListener();

            public function Main() {

                     // defining the custom contact listener

                     world.SetContactListener(customContact);

                     // calling the debug draw. This is used to show you the bitmaps are correctly applied,

                     // and because I did not want to draw the walls :)

                     debugDraw();

                     // this is the BitmapData representation of the wood

                     // check the library to see both the raw image and the sprite

                     var woodBitmap:BitmapData=new BitmapData(50,400);

                     woodBitmap.draw(new WoodImage());

                     // adding the four static, undestroyable walls;

                     addWall(320,480,640,20);

                     addWall(320,0,640,20);

                     addWall(0,240,20,480);

                     addWall(640,240,20,480);

                     // createBody builds the final body and applies the bitmap.

                     createBody(400,270,new <b2Vec2>[new b2Vec2(-25,-200),new b2Vec2(25,-200),new b2Vec2(25,200),new b2Vec2(-25,200)],woodBitmap);

                     // You can see the reason for creating the enterPointsVec in the coments in the intersection() method.

                     enterPointsVec=new Vector.<b2Vec2>(numEnterPoints);

                     // listeners

                     stage.addEventListener(MouseEvent.MOUSE_DOWN, shoot);

                     addEventListener(Event.ENTER_FRAME, update);

            }

            // my old friend debugDraw function

            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);

            }

            // function that will add the sphere and launch it

            // arguments are respectively x position, y position, radius, x velocity and y velocity

            private function addSphere(pX:Number,pY:Number,r:Number,vX:Number,vY:Number):void {

                     var theSphere:b2Body;

                     var sphereShape:b2CircleShape=new b2CircleShape(r/worldScale);

                     var sphereFixture:b2FixtureDef = new b2FixtureDef();

                     sphereFixture.density=1;

                     sphereFixture.friction=3;

                     sphereFixture.restitution=0.1;

                     sphereFixture.shape=sphereShape;

                     var sphereBodyDef:b2BodyDef = new b2BodyDef();

                     sphereBodyDef.type=b2Body.b2_dynamicBody;

                     sphereBodyDef.position.Set(pX/worldScale,pY/worldScale);

                     sphereBodyDef.bullet=true;

                     sphereBodyDef.userData={assetName:"sphere",collided:false};

                     theSphere=world.CreateBody(sphereBodyDef);

                     theSphere.CreateFixture(sphereFixture);

                     theSphere.SetLinearVelocity(new b2Vec2(vX,vY));

            }

            // simple function to add a static wall

            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);

                     wallBodyDef.userData={assetName:"wall"};

                     var wall:b2Body=world.CreateBody(wallBodyDef);

                     wall.CreateFixture(wallFixture);

                     numEnterPoints++;

            }

            // function to create and texture a dynamic body

            private function createBody(xPos:Number, yPos:Number, verticesArr:Vector.<b2Vec2>, texture:BitmapData) {

                     // I need this temp vector to convert pixels coordinates to Box2D meters coordinates

                     var vec:Vector.<b2Vec2>=new Vector.<b2Vec2>();

                     for (var i:Number=0; i<verticesArr.length; i++) {

                              vec.push(new b2Vec2(verticesArr[i].x/worldScale,verticesArr[i].y/worldScale));

                     }

                     var bodyDef:b2BodyDef = new b2BodyDef();

                     bodyDef.type=b2Body.b2_dynamicBody;

                     var boxDef:b2PolygonShape = new b2PolygonShape();

                     boxDef.SetAsVector(vec);

                     bodyDef.position.Set(xPos/worldScale, yPos/worldScale);

                     // custom userData used to map the texture;

                     bodyDef.userData={assetName:"wood",textureData:new userData(numEnterPoints,vec,texture)};

                     addChild(bodyDef.userData.textureData);

                     var fixtureDef:b2FixtureDef = new b2FixtureDef();

                     fixtureDef.density=1;

                     fixtureDef.friction=0.2;

                     fixtureDef.restitution=0.5;

                     fixtureDef.shape=boxDef;

                     var tempBox:b2Body=world.CreateBody(bodyDef);

                     tempBox.CreateFixture(fixtureDef);

                     numEnterPoints++;

            }

            // function to shoot the ball

            private function shoot(e:MouseEvent) {

                     addSphere(20,240,15,50,Math.random()*40-20);

                     stage.removeEventListener(MouseEvent.MOUSE_DOWN,shoot);

            }

            // update function to simulate and render the world

            public function update(e:Event):void {

                     world.Step(1/300, 10, 10);

                     world.ClearForces();

                     var spr:Sprite;

                     for (var b:b2Body = world.GetBodyList(); b; b = b.GetNext()) {

                              if (b.GetUserData()!=null) {

                                    // according to the collision listener, I am here when the sphere hits the wood

                                    if (b.GetUserData().assetName=="sphere"&&b.GetUserData().collided) {

                                             // retrieving sphere velocity

                                             var sphereVelocity:b2Vec2=b.GetLinearVelocity();

                                             // getting direction according to velocity

                                             var sphereDirection:Number=Math.atan2(sphereVelocity.y,sphereVelocity.x);

                                             // getting sphere position

                                             var colX:Number=b.GetPosition().x;

                                             var colY:Number=b.GetPosition().y;

                                             // clone the sphere

                                             addSphere(colX*worldScale,colY*worldScale,15,sphereVelocity.x,sphereVelocity.y);

                                             // perform the raycast

                                             world.RayCast(intersection, new b2Vec2(colX,colY), new b2Vec2(colX+5*Math.cos(sphereDirection),colY+5*Math.sin(sphereDirection)));

                                             world.RayCast(intersection, new b2Vec2(colX+5*Math.cos(sphereDirection),colY+5*Math.sin(sphereDirection)), new b2Vec2(colX,colY));

                                             // destroy the original sphere

                                             world.DestroyBody(b);

                                    }

                              }

                     }

                     // update graphics on stage

                     for (b = world.GetBodyList(); b; b = b.GetNext()) {

                              if (b.GetUserData()!=null) {

                                    spr=b.GetUserData().textureData;

                                    if (spr) {

                                             spr.x=b.GetPosition().x*worldScale;

                                             spr.y=b.GetPosition().y*worldScale;

                                             spr.rotation=b.GetAngle()*180/Math.PI;

                                    }

                              }

                     }

                     world.DrawDebugData();

            }

            private function intersection(fixture:b2Fixture, point:b2Vec2, normal:b2Vec2, fraction:Number):Number {

                     if (fixture.GetBody().GetUserData()) {

                              if (fixture.GetBody().GetUserData().textureData!=null) {

                                    var spr:Sprite=fixture.GetBody().GetUserData().textureData;

                                    // Throughout this whole code I use only one global vector, and that is enterPointsVec. Why do I need it you ask?

                                    // Well, the problem is that the world.RayCast() method calls this function only when it sees that a given line gets into the body - it doesnt see when the line gets out of it.

                                    // I must have 2 intersection points with a body so that it can be sliced, thats why I use world.RayCast() again, but this time from B to A - that way the point, at which BA enters the body is the point at which AB leaves it!

                                    // For that reason, I use a vector enterPointsVec, where I store the points, at which AB enters the body. And later on, if I see that BA enters a body, which has been entered already by AB, I fire the splitObj() function!

                                    // I need a unique ID for each body, in order to know where its corresponding enter point is - I store that id in the userData of each body.

                                    if (spr is userData) {

                                             var userD:userData=spr as userData;

                                             if (enterPointsVec[userD.id]) {

                                                      // If this body has already had an intersection point, then it now has two intersection points, thus it must be split in two - thats where the splitObj() method comes in.

                                                      splitObj(fixture.GetBody(), enterPointsVec[userD.id], point.Copy());

                                             }

                                             else {

                                                      enterPointsVec[userD.id]=point;

                                             }

                                    }

                              }

                     }

                     return 1;

            }

            // function to get the area of a shape. I will remove tiny shape to increase performance

            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 splitObj(sliceBody:b2Body, A:b2Vec2, B:b2Vec2):void {

                     var origFixture:b2Fixture=sliceBody.GetFixtureList();

                     var poly:b2PolygonShape=origFixture.GetShape() as b2PolygonShape;

                     var verticesVec:Vector.<b2Vec2>=poly.GetVertices(),numVertices:int=poly.GetVertexCount();

                     var shape1Vertices:Vector.<b2Vec2> = new Vector.<b2Vec2>(), shape2Vertices:Vector.<b2Vec2> = new Vector.<b2Vec2>();

                     var origUserData:userData=sliceBody.GetUserData().textureData,origUserDataId:int=origUserData.id,d:Number;

                     var polyShape:b2PolygonShape=new b2PolygonShape();

                     var body:b2Body;

                     // First, I destroy the original body and remove its Sprite representation from the childlist.

                     world.DestroyBody(sliceBody);

                     removeChild(origUserData);

                     // The world.RayCast() method returns points in world coordinates, so I use the b2Body.GetLocalPoint() to convert them to local coordinates.;

                     A=sliceBody.GetLocalPoint(A);

                     B=sliceBody.GetLocalPoint(B);

                     // I use shape1Vertices and shape2Vertices to store the vertices of the two new shapes that are about to be created.

                     // Since both point A and B are vertices of the two new shapes, I add them to both vectors.

                     shape1Vertices.push(A, B);

                     shape2Vertices.push(A, B);

                     // I iterate over all vertices of the original body. ;

                     // I use the function det() ("det" stands for "determinant") to see on which side of AB each point is standing on. The parameters it needs are the coordinates of 3 points:

                     // - if it returns a value >0, then the three points are in clockwise order (the point is under AB)

                     // - if it returns a value =0, then the three points lie on the same line (the point is on AB)

                     // - if it returns a value <0, then the three points are in counter-clockwise order (the point is above AB).

                     for (var i:Number=0; i<numVertices; i++) {

                              d=det(A.x,A.y,B.x,B.y,verticesVec[i].x,verticesVec[i].y);

                              if (d>0) {

                                    shape1Vertices.push(verticesVec[i]);

                              }

                              else {

                                    shape2Vertices.push(verticesVec[i]);

                              }

                     }

                     // In order to be able to create the two new shapes, I need to have the vertices arranged in clockwise order.

                     // I call my custom method, arrangeClockwise(), which takes as a parameter a vector, representing the coordinates of the shape's vertices and returns a new vector, with the same points arranged clockwise.

                     shape1Vertices=arrangeClockwise(shape1Vertices);

                     shape2Vertices=arrangeClockwise(shape2Vertices);

                     // setting the properties of the two newly created shapes

                     var bodyDef:b2BodyDef = new b2BodyDef();

                     bodyDef.type=b2Body.b2_dynamicBody;

                     bodyDef.position=sliceBody.GetPosition();

                     var fixtureDef:b2FixtureDef = new b2FixtureDef();

                     fixtureDef.density=origFixture.GetDensity();

                     fixtureDef.friction=origFixture.GetFriction();

                     fixtureDef.restitution=origFixture.GetRestitution();

                     // creating the first shape, if big enough

                     if (getArea(shape1Vertices,shape1Vertices.length)>=0.05) {

                              polyShape.SetAsVector(shape1Vertices);

                              fixtureDef.shape=polyShape;

                              bodyDef.userData={assetName:"debris",textureData:new userData(origUserDataId,shape1Vertices,origUserData.texture)};

                              addChild(bodyDef.userData.textureData);

                              enterPointsVec[origUserDataId]=null;

                              body=world.CreateBody(bodyDef);

                              body.SetAngle(sliceBody.GetAngle());

                              body.CreateFixture(fixtureDef);

                     }

                     // creating the second shape, if big enough;

                     if (getArea(shape2Vertices,shape2Vertices.length)>=0.05) {

                              polyShape.SetAsVector(shape2Vertices);

                              fixtureDef.shape=polyShape;

                              bodyDef.userData={assetName:"debris",textureData:new userData(origUserDataId,shape2Vertices,origUserData.texture)};

                              addChild(bodyDef.userData.textureData);

                              enterPointsVec.push(null);

                              numEnterPoints++;

                              body=world.CreateBody(bodyDef);

                              body.SetAngle(sliceBody.GetAngle());

                              body.CreateFixture(fixtureDef);

                     }

            }

            private function arrangeClockwise(vec:Vector.<b2Vec2>):Vector.<b2Vec2> {

                     // The algorithm is simple:

                     // First, it arranges all given points in ascending order, according to their x-coordinate.

                     // Secondly, it takes the leftmost and rightmost points (lets call them C and D), and creates tempVec, where the points arranged in clockwise order will be stored.

                     // Then, it iterates over the vertices vector, and uses the det() method I talked about earlier. It starts putting the points above CD from the beginning of the vector, and the points below CD from the end of the vector.

                     // That was it!

                     var n:int=vec.length,d:Number,i1:int=1,i2:int=n-1;

                     var tempVec:Vector.<b2Vec2>=new Vector.<b2Vec2>(n),C:b2Vec2,D:b2Vec2;

                     vec.sort(comp1);

                     tempVec[0]=vec[0];

                     C=vec[0];

                     D=vec[n-1];

                     for (var i:Number=1; i<n-1; i++) {

                              d=det(C.x,C.y,D.x,D.y,vec[i].x,vec[i].y);

                              if (d<0) {

                                    tempVec[i1++]=vec[i];

                              }

                              else {

                                    tempVec[i2--]=vec[i];

                              }

                     }

                     tempVec[i1]=vec[n-1];

                     return tempVec;

            }

            private function comp1(a:b2Vec2, b:b2Vec2):Number {

                     // This is a compare function, used in the arrangeClockwise() method - a fast way to arrange the points in ascending order, according to their x-coordinate.

                     if (a.x>b.x) {

                              return 1;

                     }

                     else if (a.x<b.x) {

                              return -1;

                     }

                     return 0;

            }

            private function det(x1:Number, y1:Number, x2:Number, y2:Number, x3:Number, y3:Number):Number {

                     // This is a function which finds the determinant of a 3x3 matrix.

                     // If you studied matrices, you'd know that it returns a positive number if three given points are in clockwise order, negative if they are in anti-clockwise order and zero if they lie on the same line.

                     // Another useful thing about determinants is that their absolute value is two times the face of the triangle, formed by the three given points.

                     return x1*y2+x2*y3+x3*y1-y1*x2-y2*x3-y3*x1;

            }

      }

}
复制代码
下面的是自定义的接触监听器：
package {

      import Box2D.Dynamics.*;

      import Box2D.Collision.*;

      import Box2D.Dynamics.Contacts.*;

      import Box2D.Common.Math.*;

      class CustomContactListener extends b2ContactListener {

            override public function PreSolve(contact:b2Contact, oldManifold:b2Manifold):void {

                     var nameA:String=contact.GetFixtureA().GetBody().GetUserData().assetName.toString();

                     var nameB:String=contact.GetFixtureB().GetBody().GetUserData().assetName.toString();

                     if ((nameA=="wood" && nameB=="sphere")||(nameA=="sphere" && nameB=="wood")) {

                              if (nameA=="sphere") {

                                    contact.GetFixtureA().GetBody().GetUserData().collided=true

                              }

                              else {

                                    contact.GetFixtureB().GetBody().GetUserData().collided=true

                              }

                     }

            }

      }

}
复制代码
我希望这会给你设计自己的游戏带来一些灵感。源码下载。
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原文地址：https://www.cnblogs.com/sode/p/2728008.html