.众所周知,box2d的DrawDebugData函数绘制默认不是放在最前面的,为了达到这个要求,v2版代码很简单

v2:

void Box2dManager::draw(){ ccGLEnableVertexAttribs( kCCVertexAttribFlag_Position );
    kmGLPushMatrix();
    box2dWorld->DrawDebugData();
    kmGLPopMatrix();
}

v3:

v3版找了很久,貌似研究的人不多,不过找的过程中,有人分析v3为了提高性能,将v2那种单独渲染变成了集中渲染,在draw中并不马上执行渲染,这时候使用代码:

void Box2dManager::draw(Renderer *renderer,const Mat4& transform,uint32_t flags){
    GL::enableVertexAttribs( GL::VERTEX_ATTRIB_FLAG_POSITION );
    Director::getInstance()->pushMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);
    box2dWorld->DrawDebugData();
    Director::getInstance()->popMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);
}

这个写法是完全从v2过度过来的,但很遗憾,并没有实现该有的功能

而根据v3方式把要渲染的顺序加入到渲染序列中,通过调用onDraw来进行上面的代码,这时候才能有效的让渲染悬浮在其他sprite之上

void Box2dManager::draw(Renderer *renderer,uint32_t flags){
    super::draw(renderer,transform,_transformUpdated);
    GL::enableVertexAttribs( cocos2d::GL::VERTEX_ATTRIB_FLAG_POSITION );
    Director* director = Director::getInstance();
    CCASSERT(nullptr != director,"Director is null when seting matrix stack");
    director->pushMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);
    _modelViewMV = director->getMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);
    _customCommand.init(_globalZOrder);
    _customCommand.func = CC_CALLBACK_0(Box2dManager::onDraw,this);
    renderer->addCommand(&_customCommand);
    director->popMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);
}

void Box2dManager::onDraw() {
    Director* director = Director::getInstance();
    CCASSERT(nullptr != director,"Director is null when seting matrix stack");
    Mat4 oldMV;
    oldMV = director->getMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);
    director->loadMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW,_modelViewMV);
    box2dWorld->DrawDebugData();
    director->loadMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW,oldMV);
}

参考:

Box2d debug drawing for cocos2d-x 3.0
B2DebugDrawLayer attachment
Cocos2d-x 3.2的渲染流程