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Overview

Flexible Subsystem Updates provide a way to call, from game code, the Update function of subsystems within the AI system. This allows developers to easily modify the order or frequency in which these subsystems are updated by:

  • Telling the AI system which subsystems are manually updated from game code, making the Update function skip updating those subsystems. This is done to prevent the same subsystems from being updated twice.
  • Manually updating the subsystems from game code. This immediately executes the Update function on the specified subsystems.

The following is a list of AI subsystems that can be manually updated from game code:

AI Subsystem
Audition Map
Behavior Tree Manager
Cluster Detector
Cover System
Movement System
Navigation System
Global Intersection Tester
Global Raycaster
Vision Map

The above subsystems can be accessed from code by typing IAISystem::ESubsystemUpdateFlag::SubsystemName, where SubsystemName corresponds to the name of the AI subsystem that you'd like to manually update.

Setting Override Update Flags

As mentioned in the Overview, the first step in modifying the order/frequency in which AI subsystems are updated, is to tell the AI system which subsystems you'd like to override. This is done by calling GetOverrideUpdateFlags only once during initialization, and setting the right flags. 

The following example demonstrates how to override the NavigationSystem AI subsystem.

Setting Override Update Flags
// Get the IAISystem from gEnv.
IAISystem* pAISystem = gEnv->pAISystem;
 
// Get the Override Update Flags structure.
// By setting the flag to 1 on the updateFlags structure, we indicate which AI subsystems we want to override to update manually.
CEnumFlags<ESubsystemUpdateFlag> updateFlags = pAISystem->GetOverrideUpdateFlags();
 
// This will will prevent the AI system from updating the subsystem (NavigationSystem, in this case) automatically.
updateFlags.Set(IAISystem::ESubsystemUpdateFlag::NavigationSystem);

Manually Updating the Subsystem

The next step is to manually call the Update function on the NavigationSystem AI subsystem by calling UpdateSubSystem on the AISystem.

Manually Update the NavigationSystem
// Game loop.
void Game::Update(const CTimeValue frameStartTime, const float deltaTime)
{
	// Get the IAISystem from gEnv.
	IAISystem* pAISystem = gEnv->pAISystem;
 
	// Call the UpdateSubSystem function, mentioning which system we want to manually update.
	pAISystem->UpdateSubSystem(frameStartTime, deltaTime, IAISystem::ESubsystemUpdateFlag::NavigationSystem); 
 
	// Update any other game systems.
	// ...
}

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