Whats the problem with bodies inside children?

cocos2d-x C++
#1

I have a sprite with a body. and it have 4 children, each one with a body (trigger)
When the sprite moves, it moves with him the 4 children…
but there is a huge delay between the movement, the parent moves first, and a lot later, (probably more than one frame update) THEN the children updates their position…

wtf.png744×328 52 KB

the higher the speed, the bigger the offset.
Im using this to add the children and bodies:

if(requiresBodyInChild)
{
     auto child = cocos2d::Node::create();
     addChild(child);
     child->setPhysicsBody(body);
}
else
{
     setPhysicsBody(body);
}

And Im letting the physics world to update the body and positions…

How to get rid of this offset???
why is it happening?
I also have tried to explicitly update the children nodes, but doesnt work.

2d "camera" follow target looks ugly
#2

Try with manual physics step in update.
setAutoStep(false) for physics.
You will find code in cpp-test

#3

its being used :frowning:
My update looks like this:

getPhysicsWorld()->step(dt);
actionLayer->update(dt);
getDefaultCamera()->update(dt);

actually changing it to the same update only made it less visible, but the problem still is there.

#4

Instead of this, try like this…

for (int i = 0; i < 3; ++i)
{
       this->getScene()->getPhysicsWorld()->step((1.0f / 180.0f));
}
#5

I tried it, and is not a real solution, since only works 3 times harder, and is not precision for movement or collision what its missing.
What I need, is just to update both at same time. but I cant achieve it anyhow.

However, the offset is smaller, as long as the body doesnt move too fast.
I guess I give up with this.

#6

Can you give me the minimum code for this to reproduce?
I will check from my-side.

#7

the code is distributed in many files, but ill try to put here the minimum necesary.
A lot of info is missing in this semi code, since im using a lot of helper classes and utils. But this is actually all you need ( the player , children, and physics settings)

The character class

class PhysicsCharacter : public virtual cocos2d::Node
{
public:

~PhysicsCharacter();

virtual void AttachBody(const std::string& bodyName, cocos2d::PhysicsBody * body);
cocos2d::PhysicsBody* CreateCircleBody(
	ColliderTags tag,
	float radius = 50.0f,
	const cocos2d::Vec2 offset = cocos2d::Vec2::ZERO,
	bool isDynamic = true,
	bool isSensor = false
);


protected:
cocos2d::Sprite* display;
//colliders
cocos2d::PhysicsBody* bodyMov;

// helper colliders
cocos2d::PhysicsBody* bodyHelperL;
cocos2d::PhysicsBody* bodyHelperR;
cocos2d::PhysicsBody* bodyHelperTL;
cocos2d::PhysicsBody* bodyHelperTR;
std::map<std::string, cocos2d::PhysicsBody*> bodiesByName;
};

The character init

bool PhysicsCharacter ::Init()
{
if(display = Sprite::CreateWithTexture("blabla.png"))  <------ pseudocode
{
	bodyMov = CreateCircleBody(_TAG::PLAYER, 50.0f, { 0,40 });
	AttachBody("player", bodyMov);

	bodyHelperTL	= CreateCircleBody(_TAG::PLAYER_HELPER, 35.0f, { -35,75 }, false, true); //  ~ dynamic , sensor
	bodyHelperTR	= CreateCircleBody(_TAG::PLAYER_HELPER, 35.0f, {  35,75 }, false, true); //  ~ dynamic , sensor
	bodyHelperL	= CreateCircleBody(_TAG::PLAYER_HELPER, 35.0f, { -35, 5 }, false, true); //  ~ dynamic , sensor
	bodyHelperR	= CreateCircleBody(_TAG::PLAYER_HELPER, 35.0f, {  35, 5 }, false, true); //  ~ dynamic , sensor
	
	AttachBody("helper", bodyHelperL);
	AttachBody("helper", bodyHelperR);
	AttachBody("helper", bodyHelperTL);
	AttachBody("helper", bodyHelperTR);

	return true;
    }
    return false;
}

character - CreateBody:

cocos2d::PhysicsBody * PhysicsCharacter::CreateCircleBody(ColliderTags tag, float radius, const cocos2d::Vec2 
offset, bool isDynamic, bool isSensor)
{
cocos2d::PhysicsBody* body = cocos2d::PhysicsBody::create();

auto shape = cocos2d::PhysicsShapeCircle::create(radius);
body->addShape(shape);
body->setPositionOffset(offset);
body->setDynamic(isDynamic);
shape->setSensor(isSensor);

body->setAngularDamping(0.0f);
body->setLinearDamping(0.0f);
body->setRotationEnable(false);
///  collision masks settings here
return body;
}

character - Attach body

void PhysicsCharacter::AttachBody(const std::string& bodyName, cocos2d::PhysicsBody * body)
{
	if(tag == _TAG::PLAYER_HELPER)
	{
	    auto child = cocos2d::Node::create();
            addChild(child);
	    child->setPhysicsBody(body);
	}
	else
	{
		setPhysicsBody(body);
	}
	body->retain();
	bodiesByName.insert({ bodyName ,body }); // keep a reference by name
}

The scene setup

   Scene::Initialize
{
    getPhysicsWorld()->setAutoStep(false);
    //getPhysicsWorld()->setSubsteps(4);             <<---- previous tests.  result:  FAIL
    //getPhysicsWorld()->setUpdateRate(120);        <<---- previous tests.  result:  FAIL
    getPhysicsWorld()->setSpeed(5.0f);
    getPhysicsWorld()->setGravity(Vec2(0, -98));
    getPhysicsWorld()->setDebugDrawMask(PhysicsWorld::DEBUGDRAW_ALL);

    schedule(schedule_selector(GS_1::update), 1.0f / 60.0f);  // default Node::update
    schedule(schedule_selector(GS_1::Update), 1.0f / 90.0f);	// physics & logic

    CHARACTER = PhysicsCharacter::Create();
    if(CHARACTER )
    {
	CHARACTER ->setPosition(250, 180);
        actionLayer->addChild(CHARACTER );
	cameraTarget = CHARACTER ;
    }
}


void Scene::update(float dt)
{
    if(cameraTarget)
    {
	auto targetPos = cameraTarget->getPosition();
	UI->setPosition(targetPos);
	getDefaultCamera()->setPosition(targetPos);
    }
    getDefaultCamera()->update(dt);
    Node::update(dt);
}

void Scene::Update(float dt)
{
    for(int i = 0; i < 4; i++)
    {
	getPhysicsWorld()->step(dt);
    }

    actionLayer->update(dt);
}