Prevent a CCT from sliding

[Minenat69]

I managed to create colliders for 3D objects as well as for my terrain, based on a Heightmap :

CLPhysicsEXTShapeHeightmap* pHeightmapShape = (CLPhysicsEXTShapeHeightmap*)_pShape;
PxHeightFieldDesc oHfDesc;
oHfDesc.format = PxHeightFieldFormat::eS16_TM;
oHfDesc.nbColumns = pHeightmapShape->m_nCols;
oHfDesc.nbRows = pHeightmapShape->m_nRows;
oHfDesc.samples.data = pHeightmapShape->m_pSamples;
oHfDesc.samples.stride = sizeof(PxHeightFieldSample);

PxHeightField* pHeightField = s_PxCreateHeightField(oHfDesc,
m_pGlobals->m_pPhysics->getPhysicsInsertionCallback());
PxHeightFieldGeometry oHfGeom(pHeightField, PxMeshGeometryFlags(), pHeightmapShape->m_fHeightScale,
pHeightmapShape->m_fRowsScale, pHeightmapShape->m_fColsScale);
PxShape* pShape = m_pGlobals->m_pPhysics->createShape(oHfGeom, *m_pGlobals->m_pConcreteMaterial);

return pShape;

To fit with the PhysX workflow, I go through the CCT to manage my controller :

PxCapsuleControllerDesc oControllerDesc;
oControllerDesc.position = PxExtendedVec3(_vPosition.x, _vPosition.y, _vPosition.z);
oControllerDesc.height = 0.875f;
oControllerDesc.radius = 0.5f;
oControllerDesc.material = m_pGlobals->m_pRubberMaterial;
oControllerDesc.behaviorCallback = &m_pGlobals->m_oControllerBehaviourCallback;

if (m_pGlobals && m_pGlobals->m_pControllerManager)
{
PxController* pController = m_pGlobals->m_pControllerManager->createController(oControllerDesc);

CLAssert(pController);
CLPhysicsEXTUserData oUserData(_nEntityID);
pController->setUserData(reinterpret_cast<void*>(oUserData.Hash()));

However, I can't manage to avoid my controller sliding along the terrain, nor keep a constant speed when it goes up a ramp.

It's not only with PxHeightmap btw, collisions between controller and PxTriangleMesh have the same issue.

Yet, it's clearly written in the SDK that the CCT is a kinematic controller to bypass issues related to friction "When the character is standing on a ramp, it should not slide. So infinite friction is needed here. When the character is moving forward on that same ramp, it should not slow down."

And I also thought I read on this Reddit post: "By default, it seems PhysX sets the "friction" on your feet to infinity, so that calling move with a downwards force (like gravity) doesn't cause you to slide down when standing on a sloped surface".

Yet, no matter what modifications I make, the capsule collider of my controller slides uniformly on the heightmap collider. It really does seems that PhysX handles the capsule controller like a regular rigid shape.
I tried changing the PxMaterials, creating my own class inheriting from PxControllerBehaviorCallback to specify the behavious flag when a collision is detected :

class CLPxControllerBehaviourCallback : public PxControllerBehaviorCallback
{
virtual physx::PxControllerBehaviorFlags getBehaviorFlags(const physx::PxShape& shape, const physx::PxActor& actor) override
{
return physx::PxControllerBehaviorFlag::eCCT_CAN_RIDE_ON_OBJECT;
}

virtual physx::PxControllerBehaviorFlags getBehaviorFlags(const physx::PxController& controller) override
{
return physx::PxControllerBehaviorFlag::eCCT_CAN_RIDE_ON_OBJECT;
}

virtual physx::PxControllerBehaviorFlags getBehaviorFlags(const physx::PxObstacle& obstacle) override
{
return physx::PxControllerBehaviorFlag::eCCT_CAN_RIDE_ON_OBJECT;
}
};but nothing works, none of my modifications seem to change anything.class CLPxControllerBehaviourCallback : public PxControllerBehaviorCallback
{
virtual physx::PxControllerBehaviorFlags getBehaviorFlags(const physx::PxShape& shape, const physx::PxActor& actor) override
{
return physx::PxControllerBehaviorFlag::eCCT_CAN_RIDE_ON_OBJECT;
}

virtual physx::PxControllerBehaviorFlags getBehaviorFlags(const physx::PxController& controller) override
{
return physx::PxControllerBehaviorFlag::eCCT_CAN_RIDE_ON_OBJECT;
}

virtual physx::PxControllerBehaviorFlags getBehaviorFlags(const physx::PxObstacle& obstacle) override
{
return physx::PxControllerBehaviorFlag::eCCT_CAN_RIDE_ON_OBJECT;
}
};

But nothing works, none of my modifications seem to change anything. Even though the breakpoint on getBehaviorFlags has beeen catched while debugging.

Is there something I might have misunderstood ? Do you have snippets of code where you create your controller and you run your physics simulations ? If so, thank you for shedding light on the subject. Thanks in advance for your answers, and have a good rest of your day !

[vreutskyy]

Thanks for the detailed report! Before digging further, could you share how you initialize PxCapsuleControllerDesc — specifically whether you set slopeLimit?

The CCT's "infinite friction" on slopes is only active when slopeLimit is non-zero. Internally, slopeLimit = 0.0 disables slope handling entirely (mHandleSlope = false), and without it the downward gravity displacement you pass to move() gets resolved via standard sweep-and-slide against the terrain normal — which is exactly what produces the lateral sliding you're seeing.

The default is 0.707 (45°), but if slopeLimit was explicitly set to 0, that would explain the behavior.

A minimal repro snippet showing your move() loop and controller setup would help confirm this.

[Minenat69]

As shown in the snippet above, I don't set manually the slopeLimit attribute, so I guess it is set by its default value.
The move statement is called in this routine :

void CLPhysicsEXT::MoveController(uint8_t _nEntityID, glm::vec3 _vMove, float _fMinDistance, float _fDeltaTime)
{
	PxControllerFilters oControllerFilters;
	if (PxController* pController = (PxController*)GetControllerForEntity(_nEntityID))
		pController->move(PxVec3(_vMove.x, _vMove.y, _vMove.z), _fMinDistance, _fDeltaTime, oControllerFilters);
}

With _vMove the displacement delta vector, which is the addition of delta vectors built via keyboard inputs (move left right, forward...) AND the gravity vector

void CLPhysicsEngine::MoveController(uint8_t _nEntityID, glm::vec3 _vMove, float _fMinDistance, bool _bApplyGravity)
{
	float fDeltaTime = GlobalDataManager::DeltaTime();
	if(_bApplyGravity)
		_vMove.y += CL_GRAVITY_CST * fDeltaTime;

	m_oPhysicsEXT.MoveController(_nEntityID, _vMove, _fMinDistance, fDeltaTime);
}

[vreutskyy]

To give you a definitive answer I'd need a self-contained runnable repro that demonstrates the wrong behavior — ideally something I can drop into the PhysX snippet framework and run directly. Without that it's hard to tell whether it's a slope angle issue, a movement logic issue, or something else entirely.

[Minenat69]

I may have found a thing I might have not understood.
To fetch positions from PhysX and send it back to my ECS, I use the same routine for rigid objects and controllers, since a CCT create an actor :

bool CLPhysicsEXT::GetResultForEntity(CLPhysicsEXTUserData _oUserData, glm::vec3& _vPosition) const
{
	if (PxRigidActor* pActor = (PxRigidActor*)GetRigidActorForEntity(_oUserData))
	{
		PxShape* pShapes[MAX_NUM_ACTOR_SHAPES];
		const PxU32 nShapes = pActor->getNbShapes();

		// Multiple shapes per actor not yet supported
		CLAssert(nShapes == 1);
		pActor->getShapes(pShapes, 1);
		const PxTransform oShapeTransform(PxShapeExt::getGlobalPose(*pShapes[0], *pActor));

		// Store result
		_vPosition = glm::vec3(oShapeTransform.p.x, oShapeTransform.p.y, oShapeTransform.p.z);
		return true;
	}
	return false;
}

Because, for me, fetch a position from the controller OR from the created actors returned the same result, but maybe not ?
The SDK has a sub-section on Hidden Actors created by the CCT, but it also says that this actor "reflects the CCT position in the physics scene", so I don't know...

EDIT : Grabbing the position from the hidden actor or the controller result in the same value.