Extending Serialization

NVIDIA PhysX SDK 3.4.1

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Extending Serialization

Introduction

The PhysX serialization system (Serialization) is extendable to custom types. If an application were to require a new joint type, for example, the serialization system could be extended to add support for serialization of that new joint type.

The following document contains some recipes and example code that show how PhysX serialization may be extended to custom types. It doesn't cover all aspects of the extension mechanisms. It is therefore advisable to look into the following implementation example for more details:

  • PhysXVehicle library (PhysXVehicle/src)

Overview

Both binary and RepX serialization can be extended for custom types. To prepare the custom type for serialization it must first inherit from PxBase. This allows instances of the custom type to be added to a PxCollection, which is a pre-requisite for serialization. The core serialization functionality needs to be provided by implementing the PxSerializer interface. The template PxSerializerDefaultAdapter provides a default implementation and can be specialized for the custom type as required. In order to support RepX serialization an additional PxRepXSerializer interface needs to be implemented. RepX serialization relies on automatic code generation using clang. Scripts to run the code generation for the examples can be found in (Tools/PhysXMetaDataGenerator).

Binary Serialization of Custom Classes

Serialization and deserialization of a custom class can be achieved with the following steps:

  1. Define a PxConcreteType and type info for the custom class. Make sure its type value is unique.
  2. The custom class needs to inherit from PxBase and implement it's interface.
  3. Instance PxSerializerDefaultAdapter<T> and implement specialized methods where necessary.
  4. If retargeting to other platforms is needed, implement getBinaryMetaData().
  5. Register the adapter and metadata, see PX_NEW_SERIALIZER_ADAPTER , PxSerializationRegistry::registerSerializer and PxSerializationRegistry::registerBinaryMetaDataCallback. Note that serializers also need to be unregistered before PxSerializationRegistry::release is called. The application is responsible for custom type serializer allocation and deallocation.

For pointer members the following needs to be done (Note that reference members are currently not supported):

  1. Implement PxSerializer::requires. It should enumerate PxBase objects on which the object depends for deserialization. See Requires.
  2. For a member pointer to another PxBase object, register the reference in the implementation of PxSerializer::registerReferences. The implementation of PxSerializer::requires may be used to help with this.
  3. Resolve references in the implementation of PxSerializer::createObject using PxDeserializationContext::resolveReference, translatePxBase.
  4. Make sure that PxSerializer::isSubordinate returns whether the object can only be serialized along with an owner object. See Subordinate.
  5. Export non PxBase data by implementing PxSerializer::exportExtraData using PxSerializationContext::writeData, alignData.
  6. Import non PxBase data in the implementation of PxSerializer::createObject using PxDeserializationContext::readExtraData, alignExtraData.

Note

In checked builds (PX_CHECKED defined as 1) metadata definitions are verified against serialized data. If metadata definitions are missing warnings are output on the error stream during re-targeting (PxBinaryConverter::convert). To avoid false warnings, all unused memory in custom serialized class instances should be marked with a 0xcd pattern. This can be done with Cm::markSerializedMem from CmUtils.h.

Note

The memory of a deserialized class instance should not be deallocated. The memory is embedded in the memory buffer containing the serialized data. The flag PxBaseFlag::eOWNS_MEMORY can used to decide whether the object memory needs be deallocated or not.

Example for a custom class:

#include "extensions/PxSerialization.h"
#include "common/PxTypeInfo.h"
#include "common/PxMetaData.h"
#include "common/PxSerializer.h"
#include "common/PxSerialFramework.h

using namespace physx;

const PxType customClassType = PxConcreteType::eFIRST_USER_EXTENSION;
PX_DEFINE_TYPEINFO(CustomClass, customClassType);

class CustomClass : public PxBase
{
    friend class PxSerializerDefaultAdapter<CustomClass>;
public:

    // constructor setting up PxBase object
    CustomClass()
    : PxBase(customClassType, PxBaseFlag::eOWNS_MEMORY | PxBaseFlag::eIS_RELEASABLE)
    {}

    // constructor called on deserialization
    CustomClass(PxBaseFlags baseFlags) : PxBase(baseFlags) {}

    virtual ~CustomClass() {}


    //PxBase
    virtual const char* getConcreteTypeName() const { return "CustomClass"; }

    virtual bool isKindOf(const char* name) const
    {
        return !strcmp("CustomClass", name) || PxBase::isKindOf(name);
    }
    //~PxBase

    //PxSerializationRegistry::registerBinaryMetaDataCallback
    static void getBinaryMetaData(PxOutputStream& stream)
    {
        PX_DEF_BIN_METADATA_VCLASS(stream, CustomClass)
        PX_DEF_BIN_METADATA_BASE_CLASS(stream, CustomClass, PxBase)

        PX_DEF_BIN_METADATA_ITEM(stream, CustomClass, PxRigidDynamic, mActor,
            PxMetaDataFlag::ePTR)
        PX_DEF_BIN_METADATA_ITEM(stream, CustomClass, char, mBuf, PxMetaDataFlag::ePTR)
        PX_DEF_BIN_METADATA_ITEM(stream, CustomClass, PxU32, mSize, 0)

        PX_DEF_BIN_METADATA_EXTRA_ITEMS(stream, CustomClass, char, mBuf, mSize, 0, 0)
    }
    //~PxSerializationRegistry::registerBinaryMetaDataCallback

private:
    PxRigidDynamic* mActor;    //add in requires
    char* mBuf;                //extra data
    PxU32 mSize;               //size of mBuf
};

//PxSerializerDefaultAdapter
template<>
void PxSerializerDefaultAdapter<CustomClass>::requires(PxBase& obj,
                                                       PxProcessPxBaseCallback& c) const
{
    CustomClass* custom = obj.is<CustomClass>();
    PX_ASSERT(custom);
    c.process(*custom->mActor);
}

template<>
void PxSerializerDefaultAdapter<CustomClass>::registerReferences(PxBase& obj,
                                                                 PxSerializationContext& s) const
{
    CustomClass* custom = obj.is<CustomClass>();
    PX_ASSERT(custom);

    s.registerReference(obj, PX_SERIAL_REF_KIND_PXBASE, size_t(&obj));
    s.registerReference(*custom->mActor, PX_SERIAL_REF_KIND_PXBASE, size_t(custom->mActor));
}

template<>
void PxSerializerDefaultAdapter<CustomClass>::exportExtraData(PxBase& obj,
                                                              PxSerializationContext& s) const
{
    CustomClass* custom = obj.is<CustomClass>();
    PX_ASSERT(custom);
    s.alignData(PX_SERIAL_ALIGN);
    s.writeData(custom->mBuf, custom->mSize);
}

template<>
PxBase* PxSerializerDefaultAdapter<CustomClass>::createObject(PxU8*& address,
                                                              PxDeserializationContext& context)
                                                              const
{
    CustomClass* custom = new (address) CustomClass(PxBaseFlag::eIS_RELEASABLE);
    address += sizeof(CustomClass);

    // resolve references
    context.translatePtr(custom->mActor);

    // import extra data
    custom->mBuf = context.readExtraData<char*, PX_SERIAL_ALIGN>();

    // return deserialized object
    return custom;
}
//~PxSerializerDefaultAdapter

void registerCustomClassBinarySerializer(PxSerializationRegistry& registry)
{
    registry.registerSerializer(customClassType, PX_NEW_SERIALIZER_ADAPTER(CustomClass));
    registry.registerBinaryMetaDataCallback(CustomClass::getBinaryMetaData);
}

void unregisterCustomClassBinarySerializer(PxSerializationRegistry& registry)
{
    PX_DELETE_SERIALIZER_ADAPTER(registry.unregisterSerializer(customClassType));
}

RepX Serialization of Custom Classes

Serialization and deserialization of a custom class can be achieved with the following steps:

  1. Perform the first three steps from Binary Serialization of Custom Classes. Methods in PxSerializer and PxSerializerDefaultAdapter<T> required exclusively for binary serialization may be left empty.
  2. Create a custom RepX serializer that implements the PxRepXSerializer interface. PxRepXSerializer is used to create an object from the xml file and write an object to the xml file. The class RepXSerializerImpl can be used to inherit default implementations of some methods.
  3. Register the general serializer adapter and the RepX serializer. Note that custom type serializers also need to be unregistered and deallocated.
  4. RepX supports automatic reading and writing of class properties. To achieve this, clang has to be used to generate corresponding metadata: PhysX API Metadata System.

Example for a custom class:

#include "SnRepXSerializerImpl.h"

const PxType customClassType = PxConcreteType::eFIRST_USER_EXTENSION;
PX_DEFINE_TYPEINFO(CustomClass, customClassType);

struct CustomClassRepXSerializer : public RepXSerializerImpl<CustomClass>
{
    CustomClassRepXSerializer(PxAllocatorCallback& inCallback)
    : RepXSerializerImpl<CustomClass>(inCallback)
    {}

    virtual PxRepXObject fileToObject(XmlReader& inReader, XmlMemoryAllocator& inAllocator,
        PxRepXInstantiationArgs& inArgs, PxCollection* inCollection)
    {
        // factory for CustomClass instance provided by application
        CustomClass* object = createCustomClass();

        // when using the PhysX API metadata system readAllProperties(...) can be used to read
        // all properties automatically
        readAllProperties(inArgs, inReader, object, inAllocator, *inCollection);

        return PxCreateRepXObject(object);
    }

    virtual void objectToFileImpl(const CustomClass* obj, PxCollection* inCollection,
                                  XmlWriter& inWriter, MemoryBuffer& inTempBuffer,
                                  PxRepXInstantiationArgs&)
    {
        // when using the PhysX API metadata system writeAllProperties(...) can be used to save
        // all properties automatically
        writeAllProperties(obj, inWriter, inTempBuffer, *inCollection);
    }

    // this can return NULL if fileToObject(...) is overwritten with a custom implementation.
    virtual CustomClass* allocateObject(PxRepXInstantiationArgs&) { return NULL; }
};

void registerCustomClassRepXSerializer(PxSerializationRegistry& registry)
{
    registry.registerSerializer(customClassType,
                                PX_NEW_SERIALIZER_ADAPTER(CustomClass));

    registry.registerRepXSerializer(customClassType,
                                    PX_NEW_REPX_SERIALIZER<CustomClassRepXSerializer>));
}

void unregisterCustomClassRepXSerializer(PxSerializationRegistry& registry)
{
    PX_DELETE_SERIALIZER_ADAPTER(registry.unregisterSerializer(customClassType));
    PX_DELETE_REPX_SERIALIZER(registry.unregisterRepXSerializer(customClassType));
}

Note

Implementing a PxRepXSerializer is currently not practical without including the internal PhysXExtension header "SnRepXSerializerImpl.h".

PhysX API Metadata System

This system produces a set of objects that are analogues of the interfaces and of descriptors in the PhysX system, all based on the public interface. The generator heuristically finds functions that start with get/set and, through a series of cascading rules, combines those into several types of properties.

Currently the generator supports the following property types:

  • Basic property
    • {ptype} get{pname}() const;
    • void set{pname}( const ptype& prop ); //plus variations
    • read-only, write-only variants of above.
  • Range property
    • void get{pname}( {ptype}& lowEnd, {ptype}& highEnd );
    • void set{pname}( {ptype} lowEnd, {ptype} highEnd );
  • Indexed property
    • {ptype} get{pname}( enumType idx );
    • void set{pname}( enumType idx, const {ptype}& prop );
  • Dual indexed property (like above, but with two enumeration indexes).
  • Collection
    • PxU32 getNb() const;
    • PxU32 get( {ptype}* buffer, PxU32 count );
    • void set({ptype}* buffer, PxU32 count);

In order to make use of the generator the following files need to be created with the following recipe:

  • CustomTypeExtensionAPI.h

    • Add all the types that should be exported to gUserPhysXTypes to this file.
    • Add the unnecessary types to gAvoidedPhysXTypes. It will not generate metadata information for these types.
    • Be sure to append the included files for these types.

  • runClang_[windows|osx|linux].[bat|sh] (e.g. runClang_windows.bat)

    • Set definition folder for these autogenerated files and set the source file in here.

    • Specify the filename of autogenerated files. Then it will generate the following files:

      include/CustomTypeAutoGeneratedMetaDataObjectNames.h
include/CustomTypeAutoGeneratedMetaDataObjects.h
src/CustomTypeAutoGeneratedMetaDataObjects.cpp

  • CustomTypeMetaDataObjects.h

    • CustomTypePropertyInfoName has to be defined and CustomTypeAutoGeneratedMetaDataObjects.h has to be included in this file. The file will then export the properties of the custom class and can be included for implementing the custom RepX serializer.

  • CustomTypeMetaDataObjects.cpp

    • This file is optional. It is only required when custom properties are needed.

PxVehicle serialization is a useful example. With Source/PhysXVehicle as the root folder the structure of the files is as follows:

src/PhysXMetaData/include/PxVehicleMetaDataObjects.h
src/PhysXMetaData/src/PxVehicleMetaDataObjects.cpp
../../Tools/PhysXMetaDataGenerator/PxVehicleExtensionAPI.h
../../Tools/PhysXMetaDataGenerator/generateMetaData.py

Running the script will auto-generate the following files:

src/PhysXMetaData/include/PxVehicleAutoGeneratedMetaDataObjectNames.h
src/PhysXMetaData/include/PxVehicleAutoGeneratedMetaDataObjects.h
src/PhysXMetaData/src/PxVehicleAutoGeneratedMetaDataObjects.cpp
  1. PxVehicleExtensionAPI.h: The type DisabledPropertyEntry is used to mark properties which do not require export. CustomProperty is for properties that need to be customized and gUserPhysXTypes is for general properties that need to be exported.
  2. runClang_[windows|osx|linux].[bat|sh]: The target directory is set to src/PhysXMetaData, and the target name is PxVehicle.
  3. PxVehicleMetaDataObjects.h: It defines the custom properties and includes PxVehicleAutoGeneratedMetaDataObjects.h
  4. PxVehicleMetaDataObjects.cpp: It implements the custom properties.

Note

The properties defined in PxVehicleAutoGeneratedMetaDataObjects.h are written to the RepX file automatically if PxVehicleMetaDataObjects.h is included for the custom RepX serializer.

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