GDC 2010 - A Dynamic Component Architecture for High Performance Gameplay - May, 2010

A Dynamic Component Architecture
for High Performance Gameplay

Terrance Cohen
Lead Systems Engineer
Insomniac Games


• Purpose

• The Dynamic Component System

• Implementation by Example

• Questions (note slide #)


• Purpose
o Statement of Problem
o Proposed Solution



Purpose : Statement of Problem

• Monolithic / deep Game Object hierarchy
o Memory: binds data @ compile time
 Allocated throughout lifetime


• Monolithic / deep Game Object hierarchy:
o Performance: poor cache coherence
 Arrays of non-homogeneous objects
 Virtual dispatch
 Fragmented instance data


o Architecture: capability <=> inheritance
 Fixed at compile time
 Fully determined by class
 Change capabilities -> change hierarchy



• "What we're used to"

• But select the best tool for the job.



• "What we're used to"

• But select the best tool for the job.

• There's a better way!

Purpose : Proposed Solution

• Construction of Game Object through composition of
components at runtime



• Simple!

• Thank you for coming!



• Simple!

• Thank you for coming!

o Oh, you want details !?!



• Small chunks

• Represent a data transformation


• Purpose

o Features


The Dynamic Component System

• Evolution
o Resistance 1 - Proof of Concept (1 type)
o Resistance 2 - "Early Adopters" (32 types)
o Ongoing (295 types as of May 1st 2010)
 Majority of new gameplay code
 Large portions of old gameplay refactored


• Evolution

• So it’s mature.


• Evolution

• So it’s mature. (No, not that way.)


• Side-by-side implementation
o Not necessary to refactor existing code
o Coexist with components

• General solution


• Does not address matters of
o Reflection
o Serialization
o Data building
o Instance versioning
o ... those things are handled separately
 outside the scope of this discussion

Dynamic Component System : Features

• Components

• High-performance

• Dynamic

• System


• Components
o Originally Aspects
o Base Component class
 8 bytes of administrative data
o Allocated from pools
 One pool per concrete type
 "Roster" indexes instances
 "Partition" separates allocated/free instances


• Components
o Small, constant-time operations
 Allocate/free
 Resolve handle
 Get type
 Type implements (derived from)
o No instance copying


• Components
o Updates per-type (per-pool)
 Cache friendly
o Encourage async update
 e.g. on SPU
 Roster: contiguous list of alloc'd instances
 Roster up to partition is DMA list


• Components
o Resolving handle
 Small, constant-time operation:
 Index into Pool
 Compare generation
 Return Component*


• Components
• Dynamic
o Runtime composition of game objects
 Dynamically alter behavior without baggage
o Component allocated == in use
o Pool sizes == max concurrent allocations


• Components
• Dynamic
o High-frequency alloc() & free()
 alloc():
 test for availability
 make handle from index & generation
 increment Roster Partition
 Component::Init()


• Components
• Dynamic
o High-frequency alloc() & free()
 alloc():
 free():
 Component::Deinit()
 swap Roster index with Partition-adjacent
index
 decrement Partition
 increment generation

Demo : DynamicComponent::Free()
  //free the component from host's component chain
  void         DynamicComponent::Free( Type type, HostHandle host_handle, Chain& chain,
                                       ComponentHandle& component_handle );


• Components
• Dynamic
• System
o Not all-or-nothing!
o Examples:
 Conversation
 Script Events
 Shots: no game object


• Purpose


o API
o Script Events: Type Registration
o Navigation: Allocation & Init
o Shots: Asynchronous Update

namespace DynamicComponent
{
  //
  // Hosts' API
  //
  // Call these from GameObjects (or other objects) that host Dynamic Components
  //
___________________________________________________________________________________________________

  //allocate a component of type, add it to host's component chain,
  //  and optionally park a prius in the component
  //  returns null if no space is available for allocation
  Component*        Allocate                  ( Type type, HostHandle host_handle,
                                                Chain* chain, void* prius = NULL );

{
//
// Hosts' API
//
//

___________________________________________________________________________________________________

//resolve a ComponentHandle to a Component
// returns NULL if component_handle is null or is a stale handle
// (i.e. component instance has been reused)
Component* ResolveHandle ( Type type, ComponentHandle component_handle );

{
//
// Hosts' API
//
//

___________________________________________________________________________________________________

//get one component of type that belongs to host
Component* Get ( Type type, HostHandle host_handle, Chain chain );

{
//
// Hosts' API
//
//

___________________________________________________________________________________________________

//get the first Component in host's chain that implements the type interface
Component* GetComponentThatImplements( Type type, HostHandle host_handle, Chain chain );

{
//
// Hosts' API
//
//

___________________________________________________________________________________________________

//get all Components of type in host's chain, up to a max of count instances.
// count should be passed with the size of the component array.
// on return, count will contain the number of matching components, up to the specified limit.
Component** GetComponents ( Type type, HostHandle host_handle,
Chain chain, u32& count );

{
//
// Hosts' API
//
//

___________________________________________________________________________________________________

//get all Components in host's chain that implement type's interface.
// count should be passed with the size of the component array.
// on return, count will contain the number of matching components, up to the specified limit.
Component** GetComponentsThatImplement( Type type, HostHandle host_handle,

{
//
// Hosts' API
//
//

___________________________________________________________________________________________________

//free the component from host's component chain
void Free ( Type type, HostHandle host_handle, Chain& chain,

{
//
// Hosts' API
//
//

___________________________________________________________________________________________________

//free all of the components in host's component chain
// (GameObjects automatically free their component chain when they are destroyed)
void FreeChain ( HostHandle host_handle, Chain& chain );

{
//
// Hosts' API
//
//

___________________________________________________________________________________________________

//downcast a Component* to one of its subclasses.
// please use this instead of the c-style '(Type*)object' so that casts are checked in debug
//Example:
// HeadComponent* my_head = COMPONENT_CAST(component_ptr, Head);
//
#define COMPONENT_CAST(component, type)
((type##Component*)ValidCast(component, DynamicComponent::type))
inline Component* ValidCast ( Component* component, Type type );

{
// Hosts' API


___________________________________________________________________________________________________

//
// Systems' API
//
// Call these from systems that use the DCS
//

//get a list of component types that implement the interface of the given component type
// count should be passed with the size of the types array.
// on return, count will contain the number of matching component types,
// up to the specified limit.
Type* GetTypesThatImplement ( Type type, u32& count );

{
// Hosts' API



//
// Systems' API
//
//

___________________________________________________________________________________________________

//returns whether component type implements interface
bool TypeImplements ( Type type, Type interface );

{
// Hosts' API



//
// Systems' API
//
//

___________________________________________________________________________________________________

//returns the number of components of type that are currently allocated
u32 GetNumAllocated ( Type type );

{
// Hosts' API



//
// Systems' API
//
//

___________________________________________________________________________________________________

//returns an array of pointers to all allocated components of type, their count,
// and their size
Component** GetComponents ( Type type, u32& count );
//returns an array of all components of type (including unallocated instances!),
// an array of the indices of allocated components within that array,
// and the count of indices
Component* GetComponentsIndexed ( Type type, u16*& indices, u32& count );

{
// Hosts' API



//
// Systems' API
//
//

___________________________________________________________________________________________________

//updates all components of those types that want to be updated in the given UpdateStage
void UpdateComponents ( UpdateStage::Enum stage );

{
// Hosts' API



//
// Systems' API
//
//

___________________________________________________________________________________________________

//frees a component that was allocated without a host, and is not in any chain
void Free ( Type type, ComponentHandle& component_handle );

{
// Hosts' API



//
// Systems' API
//
//

___________________________________________________________________________________________________

//returns the current PPU UpdateStage::Enum.
// will be UpdateStage::None unless UpdateComponents() is on the stack.
UpdateStage::Enum GetCurrentUpdateStage ( );

{
// Hosts' API



//
// Systems' API
//
//

___________________________________________________________________________________________________

//returns true iff type updates in stage
u8 GetTypeUpdateStages ( Type type );
}

{
// Hosts' API



// Systems' API

u8 GetTypeUpdateStages ( Type type );
}

Script Events : Type Registration

• Script Events are Components
o Hosted by the System
o Possibly related to a Game Object

• Registered (allocated) from Lua
o When conditions are met, call back

• Satisfaction:
1.Updated: poll their conditions
2.Notified by gameplay

Script Events : Type Registration

Notified Updated

• Checkpoint • Location
• Damage • Timer
• Death • Visible
• NumAlive
• Active
• Custom
o Reload
o Zoom
o Grapple
o SeatEnter

Script Events: Type Registration
  {
      typedef u16 Type;
      Type    unregistered_type       = 0xFFFF;
      Type    TypeRegistrar::RegisterType(
          const char*                 name,
          Type                        base_type           = unregistered_type,
          UpdateStage::Enum           update_stages       = UpdateStage::None,
          AsyncUpdateStage::Enum      async_update_stages = AsyncUpdateStage::None);
  }

Script Events: Type Registration
  {
      typedef u16 Type;
      Type    unregistered_type       = 0xFFFF;
      Type    TypeRegistrar::RegisterType(
          const char*                 name,
          Type                        base_type           = unregistered_type,
          UpdateStage::Enum           update_stages       = UpdateStage::None,
          AsyncUpdateStage::Enum      async_update_stages = AsyncUpdateStage::None);
  }

  using namespace DynamicComponent;

  void ScriptEventSystem::Init()
  {
  m_event_type        = TypeRegistrar::RegisterType("ScriptEvent");
  m_checkpoint_type   = TypeRegistrar::RegisterType("CheckpointEvent", m_event_type);
  m_location_type     = TypeRegistrar::RegisterType(
      "LocationEvent",
      m_event_type,                  //base class is ScriptEvent
      UpdateStage::PostUpdate,       //automatically updated on PPU during PostUpdate
      AsyncUpdateStage::PreUpdate);  //and on the SPU during the PreUpdate stage
  }

Navigation : Allocation & Initialization

• NavComponents are hosted by Game Objects

• Updated by the Navigation system


• Remember the API call to allocate a component:
  Component*        DynamicComponent::Allocate( Type type, HostHandle host_handle,

• WTF is a prius?


• Remember the API call to allocate a component:
  Component*        DynamicComponent::Allocate( Type type, HostHandle host_handle,

• WTF is a prius?
o initialization data
o Runtime or design-time data

• void* But is that safe!?

• Initialization
o NavQuery is the Prius for a NavComponent
o NavQuery::Submit() allocates a NavComponent, and
passes itself as the prius.
NavComponent* NavQuery::Submit(GameObject* host)
{
  DynamicComponent::Type        type      = GetComponentType(); //virtual member of NavQuery
  DynamicComponent::Component*  component = host->AllocateComponent(type, this);
  NavComponent*                 nav       = COMPONENT_CAST(component, Nav);
  return nav;
}

• host->AllocateComponent()? Helper in GameObject:
DynamicComponentComponent*
  GameObject::AllocateComponent(DynamicComponent::Type type, void* prius)
{
  return DynamicComponent::Allocate(type, m_handle, &m_component_chain, prius);
}


• Gameplay code example
void FollowerBot::Initialize(GameObject* target)
{
  Nav::GameObjectQuery source_query  (this);    //query closest point to game object
  Nav::GameObjectQuery target_query  (target);
  Nav::PathQuery       path_query    (source_query, target_query);

  Nav::PathComponent*  m_path        = path_query.Submit();
}

• When navigation components are updated, endpoints
and path are dynamically recomputed on SPU

Shots : Asynchronous Update

• Hosted by Game Object
• Replaces Projectile GameObjects

• Two DynamicComponent Type hierarchies:
o Shot represents a state machine
 Notified
o ShotAction represents the state of a Shot
 Updated
 Shared

  #ifndef SPU //PPU only

  class ShotMoveForward : public ShotAction
  {
    DERIVED_COMPONENT(ShotMoveForward, ShotAction)

  public:

    virtual void    ParkPrius    (void* prius);
    virtual void    Update       (UpdateStage::Enum stage);

  #else        //SPU only

  struct ShotMoveForward
  {
    puspu_vec4      m_location    ALIGNED(16);    //shadows ShotAction::m_next_location on PPU

  #endif       //PPU & SPU shared

    puspu_vec4      m_direction;
    f32             m_speed;
  }                               __attribute__((aligned(16)));

• ShotAction::m_next_location on PPU and
ShotMoveForward::m_location on SPU share the same address


• How? "Sentinel"
// async components must indicate where their async data begins
#define BEGIN_ASYNC_COMPONENT_DATA
    u32 m_async_data[0] __attribute__((aligned(16)));

class ShotAction : public DynamicComponent::Component
{
  COMPONENT(ShotAction);

  // ...

  DynamicComponent::Handle    m_shot;
  DynamicComponent::Type      m_shot_type;

  BEGIN_ASYNC_COMPONENT_DATA

  vec4f                       m_next_location;
};


• Purpose




• Purpose



• Thank You!
• Questions


• Visit me on the Web:
http://www.TerranceCohen.com

• Follow me on Twitter:
http://twitter.com/terrance_cohen

• Connect with me on LinkedIn:
http://www.linkedin.com/in/terrancecohen

• Ask me anything:
http://www.formspring.me/terrancecohen


Terrance Cohen
Lead Systems Engineer
Insomniac Games
www.TerranceCohen.com
Twitter: @terrance_cohen

GDC 2010 - A Dynamic Component Architecture for High Performance Gameplay - May, 2010

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