1. CISC326ix Raymond Chung ( ) Tim Crowley ( ) Jerry Mak ( ) Jashan Sudan ( ) Chris Thomas ( ) Cody Weeden ( )
Fall 2015 Project Phase 1 An explanation of Doom 3’s repository-style architecture

2. Collisions and Physics Low Level Rendering Network Interface
GSS
Visual Effects
Scene Graph
Audio
Skeletal animation
Gameplay foundation
User Interface
Collisions and Physics
Low Level Rendering
Network Interface
Human interface device
Resource Game Assets
Core System
Libraries
Sub System
Depends on

3. Core System Assertions Math Libraries
Lines of code used for error checking
Used to catch logical mistakes and violations of the programmer’s original plans
Assertions are taken out of the final product
Math Libraries
ID Software creates its own libraries to replace standard template libraries
Provides facilities for math functionally including vector and matrix math, geometric operations.

4. Core System: Memory Management
Most games tend to create their own custom memory management
Custom memory management :
ensures high speed allocations and deallocations
Limits the negative effects of memory fragmentation
Doom 3 uses “Zone Memory”, a system developed by ID Software

5. Core System: Custom Data Structures
ID Software avoids using standard template libraries and creates custom libraries, to minimize or eliminate dynamic memory allocation
ID Tech (Doom Engine) introduces intrusive list as opposed to conventional non-intrusive list.
Benefits of Intrusive List:
Less memory management: since nodes are already within the object, allocation is already done together rather than looking for various nodes in different segments of memory

6. Collision and Physics
Required in games to make objects interact with the virtual world in a reasonable way
Physics systems are responsible for realistic/semi realistic dynamic systems
Concerned with the motion (kinematics) of rigid bodies of the forces and dynamics that cause motions to occur
Doom 3 uses ID Tech (Doom Engine) for handling collisions and physics

7. Low Level Rendering in general gaming
LLR is one of the largest and most complex components of any game engine
Extremely important when applied to 3D Graphics
Low level rendering encompasses all of the raw rendering facilities of the engine.
Handles many of the pre processing tasks that are present in the game.

8. Low Level Rendering in Doom 3
Responsible for underlying data structures responsible for game operations, and preprocessing level design.
Levels are designed 2D, therefore there can be no multi-floored levels.
The game partitions floors, as 2 separate levels.

9. Binary Space Partitioning
Doom uses a Binary Space Partitioning tool, to generate a binary tree of different areas in the level
Clever way of rendering the correct areas, as a player moves through the level
When the level is changed the BSP data is updated if there’s a structural change

10. Gameplay Foundations Any action that takes place in the game
Rules, abilities, and mechanics
Implemented in the native language of the engine or a high level scripting language.
Most engines have a separate layer for gameplay foundations.
Tied to a software object model: pervades the entire engine. The term software object model refers to the set of language features and policies to implement OO software.

11. Game-Specific Subsystems
Layered above gameplay foundations; close to the “top”
Implements unique game features
eg. AI for NPCs, in-game camera angles, weapon and vehicle systems
Represents the “line” between the game engine and the game itself
Line between generic game engine and implementation of specific Doom 3 features
Coupled heavily with gameplay foundations objects

12. Game-Specific Subsystems
Doom 3 is typically in a first-person view, so player mechanics, camera objects, HID component, and the rendering engine are highly interdependent
Appearance of other features (such as monsters or powerups) is handled by the low-level renderer, and communicate with the player object as necessary
Multiple possible camera views; each is its own object (eg. death cutscenes, chase view, etc.)
Components interact in an object-oriented way

13. Resource Asset Manager
Doom 3 uses a resource manager called DeePsea
Contains packages supporting 3D object modeling, object collision resolution, etc.
Packages of game information/data is stored in special files called WADs
Either IWAD (Internal WAD) or PWAD (Patch WAD)
WADs containing related data are assembled into lumps
Example: IWAD lump called “BLOCKMAP” stores information indicating whether any two objects in a map are touching
Tied very closely to Core Systems
Contains slightly more static data than Core Systems, as opposed to applied functionality (such as math libraries, etc.)

14. HID
Games are interactive simulations so the player has to have a way of interacting with the game.  The player does this by using the HID engine.
This system is how the user interacts with the game. The user moves the character and interacts with objects usually through  keyboard and mouse or controller actions.
The HID usually doesn't use raw inputs from devices, it massage the user inputs to create smooth actions in the game.

15. HID in Doom 3
Doom was originally developed for windows in 2004 so the player controlled the game through a mouse and keyboard.
5 months later it was ported to mac and Xbox. This incorporated a Xbox controller into the Doom’s HID engine.

16. Skeletal animation
When doing skeletal animation two parts are taken into consideration, the skeleton used animate the character and the skin or mesh used to surround the skeleton.
Each vertex of the skeleton contains a list of indices showing what joint in the skeleton it is bound to and its location.
When trying to move the elbow of an arm it must first take the movement of the shoulder into consideration. To render the skeletal mesh you need the mesh, joint names, parent child relationships, the base pose of the skeleton and animation clips of the skeleton to show how it moves.

17. Skeletal animation
Animation is very memory intensive because each joint in a skeleton(often more than 100) has individual animation samples.  for this reason they are often stored in a highly compressed format.
Skeletal animation in doom 3 relates to the drawing and animation of characters, monsters and objects.

18. Network
Game model changes from layered/object oriented to a layered/object oriented/client server
Most calculations, instead of being done locally would go to a dedicated server
Core system would factor in ping for everything i.e. Collisions and physics, audio, animation etc.
Network keeps a snapshot of the game state and resolves all issues involving latency

19. Collisions and Physics Low Level Rendering Network Interface
GSS
Visual Effects
Scene Graph
Audio
Skeletal animation
Gameplay foundation
User Interface
Collisions and Physics
Low Level Rendering
Network Interface
Human interface device
Resource Game Assets
Core System
Libraries
Sub System
Depends on

20. User Interface What is it? -Heads-Up Display -In-game GUI
-Full-Motion Video
-In-game Cinematics
-In-game GUI
-In-Game Menus

21. Visual Effects What is it? -Light Mapping -HDR Lighting -PRT lighting
-Particle and Decal Systems
-Post Effects
-Environment Mapping

22. Audio System Contains at least one sound world
Handles the complexity of audio
Tracks what state they are, where the listener is and location of all of the emitters
Interacts with sound files (.wav) to play the sound

23. Scene Graph
Contains all the render models and textures in the scene/area
Interacts with the front end components ensure everything needed by the backend is uploaded to GPU ram
Handles culling and dispatches commands to the back end

24. Collisions and Physics Low Level Rendering Network Interface
GSS
Visual Effects
Scene Graph
Audio
Skeletal animation
Gameplay foundation
User Interface
Collisions and Physics
Low Level Rendering
Network Interface
Human interface device
Resource Game Assets
Core System
Libraries
Sub System
Depends on

25. Derivation Process for Architecture
Used process of elimination
Started with Pros and Cons of every architecture
Considered Implicit Invocation
Came to conclusion that a hybrid architecture would be needed
Decided on object oriented and layered
-Discuss alternatives

26. Derivation for Interacting Parts
Each person was assigned 2 subsystems to study
Came together and discussed each of our subsystems
Worked together to draw a starting conceptual architecture
Edited, reviewed and went over cases to come up with a final draft

27. What we learned! Subsystems have a lot of overlap
Focusing too much on specifics, rather than structure of overall architecture
Looking at Doom 3 regular game play, not BFG
Architectures have a lot of leeway and can change for different scenarios
We spent a lot of time doing repetitive research, when a lot of the stuff we studied had a lot of overlap, and group research would have been better