我有旋转关节的问题。当我用litlle box和revoluteJoint做一条线时，我注意到了我的第一个盒子的奇怪行为。它与其他盒子分开。
你可以在这里看到：
你可以编译它，你会看到我在说什么......
HelloWorldScene.h
// When you import this file, you import all the cocos2d classes
#import "cocos2d.h"
#import "Box2D.h"
#import "GLES-Render.h"
// HelloWorld Layer
@interface HelloWorld : CCLayer
{
b2World* world;
GLESDebugDraw *m_debugDraw;
}
// returns a Scene that contains the HelloWorld as the only child
+(id) scene;
-(void) Test;
@end
HelloWorldScene.mm
// Import the interfaces
#import "HelloWorldScene.h"
//Pixel to metres ratio. Box2D uses metres as the unit for measurement.
//This ratio defines how many pixels correspond to 1 Box2D "metre"
//Box2D is optimized for objects of 1x1 metre therefore it makes sense
//to define the ratio so that your most common object type is 1x1 metre.
#define PTM_RATIO 32
// enums that will be used as tags
enum {
kTagTileMap = 1,
kTagBatchNode = 1,
kTagAnimation1 = 1,
};
// HelloWorld implementation
@implementation HelloWorld
+(id) scene
{
// 'scene' is an autorelease object.
CCScene *scene = [CCScene node];
// 'layer' is an autorelease object.
HelloWorld *layer = [HelloWorld node];
// add layer as a child to scene
[scene addChild: layer];
// return the scene
return scene;
}
// initialize your instance here
-(id) init
{
if( (self=[super init])) {
// enable touches
self.isTouchEnabled = YES;
// enable accelerometer
self.isAccelerometerEnabled = YES;
CGSize screenSize = [CCDirector sharedDirector].winSize;
CCLOG(@"Screen width %0.2f screen height %0.2f",screenSize.width,screenSize.height);
// Define the gravity vector.
b2Vec2 gravity;
gravity.Set(0.0f, -10.0f);
// Do we want to let bodies sleep?
// This will speed up the physics simulation
bool doSleep = true;
// Construct a world object, which will hold and simulate the rigid bodies.
world = new b2World(gravity, doSleep);
world->SetContinuousPhysics(true);
// Debug Draw functions
m_debugDraw = new GLESDebugDraw( PTM_RATIO );
world->SetDebugDraw(m_debugDraw);
uint32 flags = 0;
flags += b2DebugDraw::e_shapeBit;
flags += b2DebugDraw::e_jointBit;
// flags += b2DebugDraw::e_aabbBit;
// flags += b2DebugDraw::e_pairBit;
// flags += b2DebugDraw::e_centerOfMassBit;
m_debugDraw->SetFlags(flags);
// Define the ground body.
b2BodyDef groundBodyDef;
groundBodyDef.position.Set(0, 0); // bottom-left corner
// Call the body factory which allocates memory for the ground body
// from a pool and creates the ground box shape (also from a pool).
// The body is also added to the world.
b2Body* groundBody = world->CreateBody(&groundBodyDef);
// Define the ground box shape.
b2PolygonShape groundBox;
// bottom
groundBox.SetAsEdge(b2Vec2(0,0), b2Vec2(screenSize.width/PTM_RATIO,0));
groundBody->CreateFixture(&groundBox,0);
// top
groundBox.SetAsEdge(b2Vec2(0,screenSize.height/PTM_RATIO), b2Vec2(screenSize.width/PTM_RATIO,screenSize.height/PTM_RATIO));
groundBody->CreateFixture(&groundBox,0);
// left
groundBox.SetAsEdge(b2Vec2(0,screenSize.height/PTM_RATIO), b2Vec2(0,0));
groundBody->CreateFixture(&groundBox,0);
// right
groundBox.SetAsEdge(b2Vec2(screenSize.width/PTM_RATIO,screenSize.height/PTM_RATIO), b2Vec2(screenSize.width/PTM_RATIO,0));
groundBody->CreateFixture(&groundBox,0);
//Set up sprite
[self Test];
[self schedule: @selector(tick:)];
}
return self;
}
- (void) Test {
// Circle
b2Body *circle1;
b2BodyDef bd1;
bd1.position.Set(45.0f/PTM_RATIO, 180.0f/PTM_RATIO);
bd1.type = b2_kinematicBody;
bd1.fixedRotation = false;
bd1.allowSleep = false;
circle1 = world->CreateBody(&bd1);
b2CircleShape shapecircle1;
shapecircle1.m_radius = 0.5f;
b2FixtureDef fdcircle1;
fdcircle1.shape = &shapecircle1;
fdcircle1.density = 2.0f;
fdcircle1.friction = 2.0f;
circle1->CreateFixture(&fdcircle1);
// Boxes
b2PolygonShape shape;
shape.SetAsBox(6.0f/PTM_RATIO, 0.125f);
b2FixtureDef fd;
fd.shape = &shape;
fd.density = 20.0f;
fd.friction = 0.2f;
b2RevoluteJointDef jd;
jd.collideConnected = false;
const float32 y = 9.0f;
b2BodyDef bd;
bd.type = b2_dynamicBody;
bd.position.Set(15.0f/PTM_RATIO, y);
b2Body* prevBody = world->CreateBody(&bd);
prevBody->CreateFixture(&fd);
b2Vec2 anchor(float32(0), y);
for (int32 i = 1; i < 8; ++i)
{
b2BodyDef bd;
bd.type = b2_dynamicBody;
bd.position.Set((15.0f + (i*10))/PTM_RATIO, y);
b2Body* body = world->CreateBody(&bd);
body->CreateFixture(&fd);
b2Vec2 anchor(float32(i*10)/PTM_RATIO, y);
jd.Initialize(prevBody, body, anchor);
world->CreateJoint(&jd);
prevBody = body;
}
}
-(void) draw
{
// Default GL states: GL_TEXTURE_2D, GL_VERTEX_ARRAY, GL_COLOR_ARRAY, GL_TEXTURE_COORD_ARRAY
// Needed states: GL_VERTEX_ARRAY,
// Unneeded states: GL_TEXTURE_2D, GL_COLOR_ARRAY, GL_TEXTURE_COORD_ARRAY
glDisable(GL_TEXTURE_2D);
glDisableClientState(GL_COLOR_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
world->DrawDebugData();
// restore default GL states
glEnable(GL_TEXTURE_2D);
glEnableClientState(GL_COLOR_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
}
-(void) tick: (ccTime) dt
{
//It is recommended that a fixed time step is used with Box2D for stability
//of the simulation, however, we are using a variable time step here.
//You need to make an informed choice, the following URL is useful
//http://gafferongames.com/game-physics/fix-your-timestep/
int32 velocityIterations = 8;
int32 positionIterations = 1;
// Instruct the world to perform a single step of simulation. It is
// generally best to keep the time step and iterations fixed.
world->Step(dt, velocityIterations, positionIterations);
//Iterate over the bodies in the physics world
for (b2Body* b = world->GetBodyList(); b; b = b->GetNext())
{
if (b->GetUserData() != NULL) {
//Synchronize the AtlasSprites position and rotation with the corresponding body
CCSprite *myActor = (CCSprite*)b->GetUserData();
myActor.position = CGPointMake( b->GetPosition().x * PTM_RATIO, b->GetPosition().y * PTM_RATIO);
myActor.rotation = -1 * CC_RADIANS_TO_DEGREES(b->GetAngle());
}
}
}
// on "dealloc" you need to release all your retained objects
- (void) dealloc
{
// in case you have something to dealloc, do it in this method
delete world;
world = NULL;
delete m_debugDraw;
// don't forget to call "super dealloc"
[super dealloc];
}
@end
有什么想法吗？提前致谢
答案 0 :(得分：1)
您的情况下的问题是您的第一个盒子围绕锚点旋转360度。这可能发生在第一个和最后一个框。我认为您需要限制连接的360度旋转。你已经确定了你的盒子可以达到的最大角度。您可以通过在关节中使用马达来实现。以下是Box2D手册中的一些代码，用于为关节创建电机，
b2RevoluteJointDef jointDef;
jointDef.Initialize(body1, body2, myBody1->GetWorldCenter());
jointDef.lowerAngle = -0.5f * b2_pi; // -90 degrees
jointDef.upperAngle = 0.25f * b2_pi; // 45 degrees
jointDef.enableLimit = true;
jointDef.maxMotorTorque = 10.0f;
jointDef.motorSpeed = 0.0f;
jointDef.enableMotor = true;
我希望它有所帮助。