path: root/docs/_source/ext_physx.txt

/*! \page pageextphysx PhysX Extensions

NvBlastExtPhysX contains extensions for easier use of Blast Toolkit with the PhysX SDK.
There are 3 of them:
- <b>ExtPxManager</b>: Manager to keep Blast Actors in sync with PhysX actors.
- <b>ExtImpactDamageManager</b>: Manager to collect and apply impact damage caused by collision in PhysX Scene.
- <b>ExtStressSolver</b>: Stress Solver to propagate stress through support graph and apply it as damage to Blast actors.

This library also contains an extension for synchronizing Blast state:
- <b>ExtSync</b> - Utility for writing Blast state to a buffer, to be read by a client.  This may be used for networking, for example.


<br>
\section ExtPxManager

<b>Physics Manager</b> - is a reference implementation for keeping Blast Actors synced with PhysX actors. It's main job is to listen
for TkFamily events and update \a PxScene (by adding and removing PxActors) accordingly.

In order to use it create ExtPxManager:

\code
ExtPxManager* pxManager = ExtPxManager::create(m_physics, m_tkFramework);
\endcode

For every \a TkAsset prepare \a ExtPxAsset. Which contains \a TkAsset + collection of physics geometry for every chunk. Every chunk can contain any number of subchunks.
Where each subchunk is basically PxConvexMeshGeometry with transform. Also every chunk can be marked as static (\a isStatic flag). 
If actor contains at least one static chunks in it's support graph it makes an actor kinematic (static), otherwise it's dynamic.
Having zero subchunks makes chunk invisible in physics scene, it can be used for example to represent 'earth' as a special invisible static chunk and connect all near earth chunks to it.


To create a \a ExtPxFamily from an \a ExtPxAsset:

\code 
ExtPxFamilyDesc familyDesc;
familyDesc.pxAsset = pxAsset;
familyDesc.group = tkGroup;
familyDesc.actorDesc.initialBondHealths = nullptr;
familyDesc.actorDesc.initialSupportChunkHealths = nullptr;
familyDesc.actorDesc.uniformInitialBondHealth = BOND_HEALTH_MAX;
familyDesc.actorDesc.uniformInitialLowerSupportChunkHealth = 1.0f;
ExtPxFamily* family = pxManager->createFamily(desc);
\endcode

You can subscribe to family events in order to sync graphics (or anything else) with physics:

\code
family->subscribe(listener);
\endcode

Listener will be notified with all physics actors added and removed.

And finally spawn the family in some world position (the first actor/actors will be created and event will be fired to the listener):

\code 

ExtPxSpawnSettings spawnSettings = {
	&pxScene,
	defaultPxMaterial,
	RIGIDBODY_DENSITY
};

family->spawn(PxTransform(0, 0, 0), spawnSettings);
\endcode

You can get families actor's either from listening to events or by calling getActors(). 
Every \a ExtPxActor matches 1 <-> 1 with TkActor (which matches \a NvBlastActor accordingly).

\code
ExtPxActor* actor = ....; 
physx::PxRigidDynamic rigidDynamic = actor->getPxActor(); // 
\endcode

ExtPxActor remains internally unchanged through it's life time.
Use \a ExtPxActor \a getChunkIndices() and  \a getPxActor() to update graphics representation. Sample code:

\code
	const uint32_t* chunkIndices;
	size_t chunkIndexCount;
	actor.getChunkIndices(chunkIndices, chunkIndexCount);
	for (uint32_t i = 0; i < chunkIndexCount; i++)
	{
		uint32_t chunkIndex = chunkIndices[i];
		for (Renderable* r : m_chunks[chunkIndex].renderables)
		{
			r->setTransform(actor.getPxActor()->getGlobalPose() * pxAsset.chunks[chunkIndex].convexes[0].transform);
		}
	}
\endcode

In order to use joints set joint create function with \a ExtPxManager::setCreateJointFunction(...). It will be called when new TkJoint's are
being created. All the joint updates and remove will be handled by manager internally.

<br>
\section ExtImpactDamageManager

<b>Impact Damage Manager</b> - is a reference implementation for fast and easy impact damage support. It's built on top of ExtPxManager.

In order to use it create it:

\code
ExtImpactDamageManager* impactManager = ExtImpactDamageManager::create(pxManager);
\endcode

Call it's onContact method on every \a PxSimulationEventCallback \a onContact()

\code
	class EventCallback : public PxSimulationEventCallback
	{
	public:
		EventCallback(ExtImpactDamageManager* manager) : m_manager(manager) {}

		virtual void onContact(const PxContactPairHeader& pairHeader, const PxContactPair* pairs, uint32_t nbPairs)
		{
			m_manager->onContact(pairHeader, pairs, nbPairs);
		}

	private:
		ExtImpactDamageManager*		m_manager;
	};
\endcode

Call \a applyDamage() when you want the buffered damage to be applied:

\code
impactManager->applyDamage();
\endcode

Also important to enable contact notification with custom filter shader for PxScene. \a ImpactDamageManager has a reference filter shader 
implementation which can be used for that:

\code
PxSceneDesc sceneDesc;
sceneDesc.filterShader = ExtImpactDamageManager::FilterShader;
\endcode

<br>
\section ExtStressSolver

<b>Stress Solver</b> - is a reference implementation of stress propagation using Blast support graph. 

\subsection Features Features
- Supports both static and dynamic actors
- Propagates both linear and angular momentum
- Graph complexity selection (reduces support graph to smaller size trade off speed and quality)
- Apply stress damage on Blast Actor
- Debug Render

\subsection Usage Usage

In order to use it instance stress solver by providing \a ExtPxFamily:

\code
ExtStressSolver* stressSolver = ExtStressSolver::create(family);
\endcode

And then call update() every frame:

\code
bool doDamage = true; // if you want to actually apply stress and damage actors
stressSolver->update(doDamage);
\endcode

By default it will apply scene gravity on static actors and centrifugal force on dynamic actors.
Also applyImpulse(...) can be called for additional stress to apply:

\code
stressSolver->applyImpulse(actor, position, force);
\endcode

It fully utilizes the fact that it knows initial support graph structure and does maximum of processing 
in \a create(...) method calls. After that all actors split calls are synced internally quite fast and only the actual
stress propagation takes most of computational time. 
Computational time is linearly proprtional to \a bondIterationsPerFrame setting. To fine tune look for balance 
between \a bondIterationsPerFrame and \a graphReductionLevel . The more bond iterations
are set the more precise computation will be. The smaller graph allows to make higher fidelity computations witihing 
the same bond iterations per frame (same time spent), but actual cracks (damaged bonds) will be more sparsed as the result.


<br>
\section ExtSync

<b>Synchronization Extension (NvBlastExtSync)</b> - is a reference implementation for synchronizing Blast state. 

The idea is that you can use it to write synchronization events to the buffer (on server for example) and then apply this buffer on
a client. TkFamily ID should be properly set for that.

3 types of events are supported:

- <b>ExtSyncEventType::Fracture</b>: Fracture event. Contains fracture commands information on particular TkFamily. Applied incrementally. Relatively small.
- <b>ExtSyncEventType::FamilySync</b>: Family sync event. Contains all necessary information to fully sync TkFamily state.
- <b>ExtSyncEventType::Physics</b>: Physics sync event. Contains all necessary information to fully sync ExtPxFamily state.

In order to use it create ExtSync:

\code
ExtSync* sync = ExtSync::create();
\endcode

Then let ExtSync insatnce listen to family fracture commands and write them to internal buffer:

\code
TkFamily* family = ...;
family->addListener(*sync);

// fracture family
// ....
\endcode

You can fully record TkFamily state or ExtPxFamily state at any moment by calling:

\code
sync->syncFamily(tkFamily);
// or
sync->syncFamily(pxFamily);
\endcode

Now you can take sync buffer:

\code
const ExtSyncEvent*const* buffer;
uint32_t size;
sync->acquireSyncBuffer(buffer, size);

m_savedBuffer.resize(size);
for (uint32_t i = 0; i < size; ++i)
{
	m_savedBuffer[i] = buffer[i]->clone();
}

sync->releaseSyncBuffer();
\endcode

On the client you can then apply this buffer:

\code
sync->applySyncBuffer(tkFramework, m_savedBuffer.data(), m_savedBuffer.size(), group, pxManager);
\endcode

ExtPxManager is required only if sync buffer contains ExtSyncEventType::Physics events.


<br>

*/