How to detect a touch inside a box2d fixture created by PhyicsEditor in Cocos2d-x?

Question

My testing environment:

Xcode 4.6, New cocos2d-x+box2d project cocos2d-2.1beta3-x-2.1.1 PhysicsEditor 1.0.10

I modified a bit in HelloWorldScene of PhysicsEditor cocos2dx demo to make it simpler, Here are some of my code:

1. initPhysics

   gravity.Set(0.0f, 0.0f);

So that the sprite will not move.

2. Replace source code inside ccTouchesEnded to:

   CCTouch* pTouch = (CCTouch *)touches->anyObject();

   CCPoint location = pTouch->locationInView(pTouch->view());

   CCPoint convLoc = CCDirector::sharedDirector()->convertToGL(location);

   b2Vec2 v = b2Vec2(convLoc.x/PTM_RATIO, convLoc.y/PTM_RATIO);

   for (b2Body *b = world->GetBodyList(); b; b = b->GetNext()) {

   b2Fixture *f = b->GetFixtureList(); // get the first fixture
   CCSprite *sprite =(CCSprite *) b->GetUserData();
   
   if(sprite != NULL)
   {
       if(f -> TestPoint(v))
       {
           CCLog("You touched a body %d",sprite->getTag());
       }
   }
   

   }

The problem is that TestPoint only return true in a very small area (not for whole shape area).

Here is the screenshot:

Can anybody suggest how I debug this problem? Thanks

Updated: showing the generated data from PhysicsEditor

Answer 1

The problem is that you only probe for the first fixture. But complex bodies are made from several. The reason is that

• Box2d only allows 8 vertexes per fixture
• Box2d can only work with convex shapes

This is why complex shapes are decomposed into a list of polygons.

Iterate over the fixture list instead.

b2Fixture *f = body->GetFixtureList();
while(f)
{
    if(f -> TestPoint(v))
    {
        CCLog("You touched a body %d",sprite->getTag());
    }
    f = f->GetNext();            
}