VR-Forces Simulation Engine Architecture

Table of Contents

• Overview
• Doubled Buffered State
• Threading Model
  • Begin Frame
  • Object Tick
  • Network Tick
  • Advance Frame

Overview

The VR-Forces Simulation Engine is responsible for updating all object state for each simulation frame, and publishing the updated state to the network. In order to accomplish this, the simulation engine provides data to the simulation models to take into account when computing updated state, including the state of other objects in the world (potentially received from the network), the terrain, weather, messages, and much more. All interaction with the simulation engine is done though network messages.

All persistent state in VRF Sim is maintained in VRF Objects, using the DtLocalObject class. These objects include:

• Entities
• Tactical Graphics
• Weather and Dynamic Terrain These objects have components (subclassed from DtSimComponet) which update object state over time to give each object the desired behavior. These components may send and receive events (DtEvent) to communicate with each other or with other simulated objects. These events include:
• Detonations
• Radio Messages
• Simulation Control Messages

The DtCgf class is the primary top level class in a VR-Forces Simulation Engine. It creates and owns all other classes that make up a VR-Forces simulation engine. This includes the Sim Manager, DtSimManager, which owns all of the other managers.

VR-Forces Simulation Engine Major Class Relationships

The simulation is run over a series of frames. Each call to DtCgf::tick() executes a single frame of the simulation. Most components of VR-Forces Simulation Engine have a tick() function which is called once per frame as a result of the top level DtCgf::tick().

Doubled Buffered State

The External State data of each object in the simulation is double buffered. This means that there are two copies of this data, referred to as Current Frame State and Next Frame State.

Threading Model

The VR-Forces Simulation Engine is a multithreaded application that can take advantage of many CPUs on the same physical hardware. Each simulation frame is broken into four major parts:

• Begin Frame
• Object Tick
• Network Tick
• Advance Frame

The double buffered state data for objects allows VR-Forces to simulate local objects using multiple threads, even when the objects need to access state of other objects in the simulation without requiring locking each time cross-object state is accessed.

VR-Forces Simulation Engine Sequence Diagram

Begin Frame

This section runs at the start of each frame, and sets up any necessary data structures and subsystems for use during the frame execution. This section includes:

• Resetting the spaitial organization of objects.
• Updating the navigation mesh subsystem with new entity positions.
• Processing and dispatching events generated during the previous frame.

Object Tick

This section runs all the simulation logic for local objects simulated by the engine by calling the DtLocalObject::tick() for each local object simulated by the engine. This is typically the most processor intensive section of the simulation engine.

Multiple threads are used during Object Tick, and objects are distributed among the threads to execute simultaniously. Each DtLocalObject and all its subcomponents are always executed by the same thread, so data can be set and accessed freely within a single DtLocalObject, but other DtLocalObject instances cannot be accessed, as they are running in other threads at the same time.

Note

Object Tick runs in parallel with Network Tick.

Network Tick

This section synconizes the local engine data with the simulation network by calling tick() on the DtSimObjectNetInterface instances as well as other NetInterface classes.

• For all locally simulation objects, the Current Frame State data is copied into VR-Link state reposities, and the VR-Link Publisher classes are ticked to send out state updates as necessary.
• For all remote objects, state data is copied from the VR-Link state reposities into the Next Frame State data of the engine.

Depending on the configuration, there may be multiple threads used for Network Tick, and the DtSimObjectNetInterface instances will be distributed among the available threads.

Note

Network Tick runs in parallel with Object Tick.

Advance Frame

This section ends the execution of the frame by copying all needed data from the Next Frame State into Current Frame State.

Advance Frame runs once both Object Tick and Network tick have completed.