Read/Write an Atoms cache

Owned by Alan Stanzione
Last updated: Aug 16, 2017 by Daniele Federico
5 min read

Atoms has its own internal format for agent caches, please check the reference to know more about what files is made of.

Cache header

The cache header is a MapMetadata cointaining the following key-value pairs:

  • agentIds: an IntArrayMetadata containing all the agents ids
  • cacheType: a StringMetadata,for internal use only and it must store the value "dynamic"
  • endFrame: an IntMetadata containing the end frame
  • startFrame: an IntMetadata containing the start frame

This file must have the following name extension: atoms (i.e. test_cache.atoms)

Agent types

To make the caches more portable, all the agent type files are saved in a "agentTypes" subfolder next to the cache files.

The agent type are serialized in a binary format:

Atoms::AgentTypePtr agentType = agent->agentType();
AtomsCore::Archive agentTypeArchive(agentType->memSize());
agentType->serialize(agentTypeArchive);
agentTypeArchive->writeToFile("myAgentType.agentType")

 

To make an agent type visible inside the Atoms UI, an event simulation python wrapper script is exported in the same folder.

std::string cachePath = "/atomsDemo/cache/";
std::string agentType = agent->agentType().name();

Atoms::AgentTypePtr agentTypePtr = agent->agentType();
AtomsCore::Archive agentTypeArchive(agentTypePtr->memSize());
agentTypePtr->serialize(agentTypeArchive);
agentTypeArchive->writeToFile(cachePath + "/agentTypes/"  + agentType + ".agentType")


//store the python event wrapper
	const std::string pythonEvent =	
	"import AtomsCore\n"
	"import Atoms\n"
	"import imath\n"
	"\n"
	"class "+ agentType +"Cached(Atoms.SimulationEvent):\n"
	"\tagentTypeFile = r'" + agentTypePath + "'\n"
	"\teventName = '" + agentType + "Cached'\n"
	"\tagentTypeName = '+ agentType + '\n"
	"\tgeoPath = ''\n"
	"\tskinPath = ''\n"
	"\tstateMachine = ''\n"
	"\n"
	"\tdef __init__(self):\n"
	"\t\tAtoms.SimulationEvent.__init__(self)\n"
	"\t\tself.setName(self.eventName)\n"
	"\n"
	"\tdef load(self):\n"
	"\t\taType = Atoms.AgentType()\n"
	"\t\taTypeArchive = AtomsCore.Archive()\n"
	"\t\tif aTypeArchive.readFromFile(self.agentTypeFile):\n"
	"\t\t\taType.deserialise(aTypeArchive)\n"
	"\t\telse:\n"
	"\t\t\treturn\n"
	"\n"
	"\t\tif self.geoPath:\n"
	"\t\t\tmeshMap = AtomsCore.MapMetadata()\n"
	"\t\t\ttypeArchive = AtomsCore.Archive()\n"
	"\t\t\tif typeArchive.readFromFile(self.geoPath):\n"
	"\t\t\t\tmeshMap.deserialise(typeArchive)\n"
	"\t\t\t\taType.metadata()["lowGeo"] = meshMap\n"
	"\n"
	"\t\tif self.skinPath:\n"
	"\t\t\tskinMap = AtomsCore.MapMetadata()\n"
	"\t\t\tskinArchive = AtomsCore.Archive()\n"
	"\t\t\tif skinArchive.readFromFile(self.skinPath):\n"
	"\t\t\t\tskinMap.deserialise(skinArchive)\n"
	"\t\t\t\taType.metadata()["skinGeo"] = skinMap\n"
	"\n"
	"\t\taType.metadata()["stateMachine"] = AtomsCore.StringMetadata(self.stateMachine)\n"
	"\n"
	"\t\tAtoms.AgentTypes.instance().addAgentType(self.agentTypeName, aType)\n";

	std::string agentTypeWrapperPath = cachePath  + "/agenTypes/" + agentType + ".py";
	std::ofstream out(agentTypeWrapperPath);
    out << pythonEvent;
    out.close();
CACHED_AGENT_TYPE_SCRIPT = '''
import AtomsCore
import Atoms

class AgentTypeEvent$(Atoms.SimulationEvent):
\tagentTypeFile = r'agentTypeFile$'
\teventName = 'agentType$'
\tagentTypeName = 'agentTypeName$'
\tgeoPath = ''
\tskinPath = ''
\tstateMachine = ''

\tdef __init__(self):
\t\tAtoms.SimulationEvent.__init__(self)
\t\tself.setName(self.eventName)

\tdef load(self):
\t\taType = Atoms.AgentType()
\t\taTypeArchive = AtomsCore.Archive()
\t\tif aTypeArchive.readFromFile(self.agentTypeFile):
\t\t\taType.deserialise(aTypeArchive)
\t\telse:
\t\t\treturn

\t\tif self.geoPath:
\t\t\tmeshMap = AtomsCore.MapMetadata()
\t\t\ttypeArchive = AtomsCore.Archive()
\t\t\tif typeArchive.readFromFile(self.geoPath):
\t\t\t\tmeshMap.deserialise(typeArchive)
\t\t\t\taType.metadata()["lowGeo"] = meshMap

\t\tif self.skinPath:
\t\t\tskinMap = AtomsCore.MapMetadata()
\t\t\tskinArchive = AtomsCore.Archive()
\t\t\tif skinArchive.readFromFile(self.skinPath):
\t\t\t\tskinMap.deserialise(skinArchive)
\t\t\t\taType.metadata()["skinGeo"] = skinMap

\t\taType.metadata()["stateMachine"] = AtomsCore.StringMetadata(self.stateMachine)

\t\tAtoms.AgentTypes.instance().addAgentType(self.agentTypeName, aType)
'''

agentType = "atomsRobot"

# This serialize the agent type in python
aType = Atoms.AgentTypes.instance().agentType(agentType)
if aType:
  atArchive = AtomsCore.Archive(aType.memSize())
  aType.serialise(atArchive)
  atArchive.writeToFile(os.path.join(agentTypesPath, "%s.agentType" %
                                               (agentType)))

agentTypesPath = "/atomsDemo/cache/test_cache/agentTypes/"

agentTypeScript = CACHED_AGENT_TYPE_SCRIPT

af = os.path.normpath(os.path.join(agentTypesPath, "%s.agentType" %
                                               (agentType)))

agentTypeScript = agentTypeScript.replace("agentTypeFile$", af)
agentTypeScript = agentTypeScript.replace("agentType$","%sCached" %
                                                      agentType)
agentTypeScript = agentTypeScript.replace("agentTypeName$",
                                                      agentType)
agentTypeScript = agentTypeScript.replace("AgentTypeEvent$",
                                                      "%sCached" % (agentType))

with open(os.path.join(agentTypesPath, "%s.py" % (agentType)), "w") as pyFile:
	pyFile.write(agentTypeScript)
	pyFile.close()

Frame files

The cache has these four files per frame:

  • header: basic info such as number of agents at the current frame, number of created agents and number of deleted agents
  • frame: agent data such as agent type, position, velocity, bbox and variation
  • meta: agents metadata
  • pose: agent skeleton data
Header file

The cache frame header is a MapMetadata cointaining the following key-value pairs:

  • agents: an IntArrayMetadata containing all the agents ids
  • agentsCreated: an IntArrayMetadata containing the ids of the created agents at this frame.
  • agentsDeleted: an IntArrayMetadata containing the ids of the deleted agents at this frame.
  • box: an BoxMetadata containing the bounding box at the current frame

This file has the following extension: .$FRAME.header.atoms (i.e. test_cache.0010.header.atoms)

Frame file

The cache frame is a MapMetadata. Each entry in this map uses the agent id as key while the value is another MapMetadata containing the following key-value pairs:

  • agentType: StringMetadata containing the agent type name
  • box: BoxMetadata containing the agent bounding box
  • position: Vector3Metadata containing the agent position
  • variation: StringMetadata containing the agent variation
  • velocity: Vector3Metadata containing the agent velocity


This is an example of frame data:

  • "0":
    - "agentType": StringMetadata("atomsRobot")
    - "box": BoxMetadata(AtomsCore::Box(AtomsCore::Vector3(-10,-10,-10),AtomsCore::Vector3( 10, 10, 10)))
    - "position": Vector3Metadata(AtomsCore::Vector3(0,0,0))
    - "velocity": Vector3Metadata(AtomsCore::Vector3(1.4354,0.234,0.54433))
  • "1":

    - "agentType": StringMetadata("atomsRobot")
    - "box": BoxMetadata(AtomsCore::Box(AtomsCore::Vector3(-50,-10,-50),AtomsCore::Vector3(-40, 10, -40)))
    - "position": Vector3Metadata(AtomsCore::Vector3(-45,0,0))
    - "velocity": Vector3Metadata(AtomsCore::Vector3(1.5464,0.124,0.76433))

  • "5":
    - "agentType": StringMetadata("atomsRobot")
    - "box": BoxMetadata(...)
    - "position": Vector3Metadata(...)
    - "velocity": Vector3Metadata(...)
  • ...

This file has the following extension: .$FRAME.frame.atoms (i.e. test_cache.0010.frame.atoms)

Metafile

The cache meta file is a MapMetadata. Each entry in this map uses the agent id as key while the value is another MapMetadata containing all the metadatas of the agent

This is an example:

  • "0":
    - "position": Vector3Metadata(...)
    - "direction": Vector3Metadata(...)
    - "state": IntMetadata(...)
    - ...
  • "1":

    - "position": Vector3Metadata(...)
    - "direction": Vector3Metadata(...)
    - "state": IntMetadata(...)
    - ...

  • "1":

    - "position": Vector3Metadata(...)
    - "direction": Vector3Metadata(...)
    - "state": IntMetadata(...)
    - ...

  • ...

This file must have the following extension: .$FRAME.meta.atoms (i.e. test_cache.0010.meta.atoms)

Pose file

The cache pose file is a MapMetadata. Each entry in this map uses the agent id as key while the value is a PoseMetadata that store the agent pose.

This file has the following extension: .$FRAME.pose.atoms (i.e. test_cache.0010.pose.atoms)

Writing an Atoms cache

An atoms cache can be exported using the AtomsCache::exportCacheFrame() function. This function exports only the frame files, the header and the agents type must be exported separately.

#include <Atoms/AtomsCache

std::string cachePath = "/atomsDemo/cache/";
std::string cacheName = "cache_test";
int startFrame = 1;
int endFrame = 2;

// list of agents groups to export
std::vector<AtomsPtr<Atoms::AgentGroup>> agentGroups;

// if you are in maya or houdini you can get the agent groups from the agents simulation
auto sims = Atoms::AgentsSimulations::instance()
auto sim = sims.begin().second;
for(unsigned int i=0; i < sim.numAgentGroups(); i++)
{
	agentGroups.push_back(sim.agentGroup(i));
}

// This maps the agent global id with the cache id 
std::unordered_map<size_t, size_t> cacheIdMap;

std::set<std::string> agentTypes;

// Add compression and use multithread 
size_t tags = AtomsCore::Archive::kRandomAccessCompress | AtomsCore::Archive::kMultithread;


for (unsigned int frame = startFrame; frame < endFrame; frame++)
{
	AtomsCache::exportCacheFrame(cachePath, cacheName, frame, agentGroups, cacheIdMap, agentTypes, tags);
}

// save the agent types
Atoms::AgentTypes& agentTypes = Atoms::AgentTypes::instance();
for(const std::string agentType: agentTypes)
{
	auto agentTypePtr = agentTypes->agentType(agentType);
	if (!agentTypePtr)
		continue;
	AtomsCore::Archive agentTypeArchive(agentTypePtr->memSize());
	agentType->serialize(agentTypeArchive);
	std::string agentTypePath = cachePath  + "/agenTypes/" + agentType + ".agentType";
	agentTypeArchive->writeToFile(agentTypePath);

	//store the python event wrapper
	const std::string pythonEvent =	
	"import AtomsCore\n"
	"import Atoms\n"
	"import imath\n"
	"\n"
	"class "+ agentType +"Cached(Atoms.SimulationEvent):\n"
	"\tagentTypeFile = r'" + agentTypePath + "'\n"
	"\teventName = '" + agentType + "Cached'\n"
	"\tagentTypeName = '+ agentType + '\n"
	"\tgeoPath = ''\n"
	"\tskinPath = ''\n"
	"\tstateMachine = ''\n"
	"\n"
	"\tdef __init__(self):\n"
	"\t\tAtoms.SimulationEvent.__init__(self)\n"
	"\t\tself.setName(self.eventName)\n"
	"\n"
	"\tdef load(self):\n"
	"\t\taType = Atoms.AgentType()\n"
	"\t\taTypeArchive = AtomsCore.Archive()\n"
	"\t\tif aTypeArchive.readFromFile(self.agentTypeFile):\n"
	"\t\t\taType.deserialise(aTypeArchive)\n"
	"\t\telse:\n"
	"\t\t\treturn\n"
	"\n"
	"\t\tif self.geoPath:\n"
	"\t\t\tmeshMap = AtomsCore.MapMetadata()\n"
	"\t\t\ttypeArchive = AtomsCore.Archive()\n"
	"\t\t\tif typeArchive.readFromFile(self.geoPath):\n"
	"\t\t\t\tmeshMap.deserialise(typeArchive)\n"
	"\t\t\t\taType.metadata()["lowGeo"] = meshMap\n"
	"\n"
	"\t\tif self.skinPath:\n"
	"\t\t\tskinMap = AtomsCore.MapMetadata()\n"
	"\t\t\tskinArchive = AtomsCore.Archive()\n"
	"\t\t\tif skinArchive.readFromFile(self.skinPath):\n"
	"\t\t\t\tskinMap.deserialise(skinArchive)\n"
	"\t\t\t\taType.metadata()["skinGeo"] = skinMap\n"
	"\n"
	"\t\taType.metadata()["stateMachine"] = AtomsCore.StringMetadata(self.stateMachine)\n"
	"\n"
	"\t\tAtoms.AgentTypes.instance().addAgentType(self.agentTypeName, aType)\n";

	std::string agentTypeWrapperPath = cachePath  + "/agenTypes/" + agentType + ".py";
	std::ofstream out(agentTypeWrapperPath);
    out << pythonEvent;
    out.close();
}


// write the cache header
AtomsCore::IntArrayMetadata agentIdsMeta;
std::vector<int>& agentIdsVec = agentIdsMeta.get();
agentIdsVec.reserve(cacheIdMap.size());
for (auto it=cacheIdMap.begin(); it != cacheIdMap.end(); it++)
{
	agentIdsVec.pushBack(it->second);
}

std::sort(agentIdsVec.begin(), agentIdsVec.end());

AtomsCore::MapMetadata cacheHeader;
cacheHeader.addEntry("startFrame", &AtomsCore::IntMetadata(startFrame));
cacheHeader.addEntry("endFrame", &AtomsCore::IntMetadata(endFrame));
cacheHeader.addEntry("cacheType", &AtomsCore::StringMetadata("dynamic"));
cacheHeader.addEntry("agentIds", &agentIdsMeta);

Reading an Atoms cache

Since the Atoms cache is made of different serialized MapMetadata you can read them using the atoms serialization system.

If you are going to query multiple times different cache frames during a simulation, you can use the cache manager to increase the performance.

Copyright © 2017, Toolchefs LTD.