Game Programming
(Game Architecture)
2016. Spring
Real-Time Software
■ Video games
 Real-time software applications
• Data acquisition and response must be performed under
time-constrained conditions
 The internal of the system
• A data acquisition module (ex. Physical radar)
• A display/computation module (ex. Help Ground personnel
visualize data)
• An interaction module (ex. To send signals to planes)
Real-Time Software
■ Games
 Time dependent interactive application
• Virtual world simulator
 Feeds real-time data (Part I)
• Presentation module
 Displays it (Part II)
• Control mechanisms
 Allow the player to interact with the world
 Game programming is about trying to defy that limit and
creating something beyond the platform’s capabilities
Real-Time Loops
■ All real-time interactive application
 Three takes running concurrently
• The state of the world must be constantly recomputed
• The operator must be allowed to interact with it
• The resulting state must be presented to the player
 Using onscreen data, audio, and any other output device
available
 Two portions
• An update and a render routine
• Both run simultaneously
 In an ideal world  parallel processors
 Most Computers
− Single processor with limited memory and speed
Real-Time Loops
■ Coupled Approach
 Implement both routine in a loop
 Each update is followed by a render call (equal importance)
 Problem
• Performance variation
 Frame-per-second(FPS) rate varies
due to system performance
 The render and update sections in sync
makes coding complex
− Update  fixed frequency
− Render  variant frequency
Coupled Approach
Real-Time Loops
 One solution
• Update and render would be in a loop
• But, the granularity of the update portion would depend on
the H/W speed
• Valid solution, but worthless
 Decision making is a complex process
Real-Time Loops
■ Twin-threaded approach
Twin-thread Approach
 One thread executes the rendering portion while the other
take care of the world updating
Ex) game render  60 fps, AI update  15 fps
• Only one of every 4 frames will carry out an AI update
 More frames means nothing
− All the frame in an AI cycle look exactly the same
• Solution
 AIs are broken down two sections
− Real AI code : fixed time step
− Simpler routine such as animation interpolation and
trajectory update routine : a per–frame basis
 The idea is very good but does not implement well on some
H/W platform
Real-Time Loops
■ Single thread fully decoupled
 Decouple the render from the update routine
• Render is called as often as possible
• Update is synchronized with time
 Storing a time stamp for update call
 Better control than thread and simpler programming
long timelastcall=timeGetTime();
while (!end) {
if ((timeGetTime()-timelastcall) > 1000/frequency) {
game_logic();
timelastcall=timeGetTime();
}
presentation();
}
Poor man’s thread Approach
The Game Architecture
■ Game Framework
 The Game Logic Section (Update)
• Updating the player
• Updating the world
• Updating the nonplaying characters (NPCs)
 The Presentation Section (Render)
• Rendering the game world
• Rendering NPCs
• Rendering the player
The Game Logic Section
■ Player Update
 Player input module
• Interaction requests by the player must be checked for
• Control mechanism (Ch. 5)
 Joysticks, keyboards, mouses, …
 Use abstract device controller
− The game code does not actually interact with the
physical controller
 Player restriction routine (the hardest of the three)
• Restrictions to player interaction
• Ex) collision detection (Ch. 21), logical restrictions
 Player update routine
• Player see the result of their interactions
The Game Logic Section
■ World Update
 Game world entities
• Passive elements
 Items that belong to the world game
 but do not have an attached behavior
 Ex) walls, scenario items
• Active elements
 Those that have an embedded behaviors
 Logic based elements
− Ex) doors, elevators, or moving platforms, decorative
elements (flying birds)
 AI based elements
− Ex) enemies
The Game Logic Section
■
The processing of updating active elements
1. Sort according to relevance
• A filter will select those elements that are relevant to the
gameplay
• Ex) LOD (Level of Detail)
2. The state of the active elements must be updated
• Logical entities
 Execute control mechanism
 Update state
•
Intelligent entities (flight simulator)
 Goals and current state must be analyzed (obtaining pos, heading, state of
the weapon systems, damage)
 Restrictions must be sensed
(avoiding collision)
 A decision/plan making engine must be implemented that
effectively generates behavior rules (chase the player, blow it up)
 Update the world state accordingly (store data  the enemy moved,
or eliminate it from the DB if it was shot down)
The Game Logic Section
Game logic
Player update
Sense player input
Compute restrictions
Update player state
World update
Passive elements
Pre-select active zone for engine use
Logic-based elements
Sort according to relevance
Execute control mechanism
Update state
AI Based elements
Sort according to relevance
Sense internal state and goals
Sense restrictions
Decision engine
Update world state
End
The Presentation Section
■ World Rendering
 Render visually and sonically the game world
 Focus on the passive elements(ex. wall, ground) and simple
logical-based devices(ex. opening door) of the world
 World rendering pipeline
• Selecting the relevant subset
• Taking care of the actual rendering
The Presentation Section
■ World Rendering
 Graphics pipeline
• Reduce to the visual part
 Clipping, culling and computing occlusions
• Assigned a suitable LOD (option)
 Ex) 500m tree (10,000 triangles)  occupy single pixel ??
• Geometry packing
• Packed geometry is sent to the Graphics H/W
 Actual paint it on screen
 Audio rendering
• Filtering
 Can’t just filter what is visible and what is not.
 Using some distance versus volume metric
• Attenuation can be computed
• Sending the audio files to the sound card
The Presentation Section
■ NPC Rendering
Need specific pipeline due to their animation properties
 Filtering the character lists (more expensive)
• Visibility step
• Use an LOD pass (option)
 Animation routine must be computed
• From key framed to skeletal animations and so on
 Static geometry data that represents the current snapshot of
how the character must look for a given frame
 Packed using an efficient representation
 Sent to the H/W for display
The Presentation Section
■ The Player
 Nothing but a very special case NPC
 Rendering pipeline is simpler
• The player is generally visible
 No need to check him for visibility
• No need for LOD processing
 Use high resolution meshes
 Player Rendering Pipeline
• Animation step (High quality)
• Packing
• Render step
The Presentation Section
Game presentation
World presentation
Select visible subset (graphics)
Clip
Cull
Occlude
(Select resolution)
Pack geometry
Render world geometry
Select audible sound sources (sound)
Pack audio data
Send to audio Hardware
NPC presentation
Select visible subset
(Select resolution)
Animate
Pack
Render NPC data
Player presentation
Animate
Pack
Render
End
Game Framework
Complete game framework
Game logic
Player update
Sense player input (chap. 5)
Compute restrictions (chap. 22)
Update player state
World update (chap. 6-9)
Passive elements (chap. 4)
Pre-select active zone for engine use
Logic-based elements
Sort according to relevance
Execute control mechanism
Update state
AI Based elements
Sort according to relevance
Sense internal state and goals
Sense restrictions
Decision engine
Update world state
End
Game presentation
World presentation (chap. 6-14, 17-21)
Select visible subset (graphics)
Clip
Cull
Occlude
(Select resolution)
Pack geometry
Render world geometry
Select audible sound sources (sound)
Pack audio data
Send to audio Hardware
NPC presentation (chap. 15)
Select visible subset
(Select resolution)
Animate
Pack
Render NPC data
Player presentation (chap. 15)
Animate
Pack
Render
End
End
Networked Game
Architecture
■ Networked Game (chap. 10)
 From another player’s standpoint, your character is really just
an NPC
 Some minor changes
• Player update section
 every player update is followed by a broadcast message that
sends the newly computed position to other gamers
• AI system
 A special type of AI module
− Receive data from the communications channel
− Reflects it to the logical gaming environment
Networked Game
Architecture
Game logic
Player update
Sense player input
Compute restrictions
Update player state
Broadcast player state
World update
Passive elements
Pre-select active zone for engine use
Logic-based elements
Sort according to relevance
Execute control mechanism
Update state
AI Based elements
Sort according to relevance
Sense internal state and goals
Sense restrictions
Decision engine
Automatic AI module
Special-case AI module (Receive data from N/W, Reflect it to the logic)
Update world state
End
The Programming Process
■ The stages of game project
 Preproduction
• Working prototype of the game
 Help establish workflows, test the content and technology production pipeline
 Help build an accurate picture of the road ahead
− Budget, milestones, team structure
 This demo will also used to showcase the potential of the game to customers
and publisher
 Production (long process: 1-3 years)
• Divide into milestones (both monthly and trimonthly)
 Make sure the game development at the desired speed
 Show the publisher the rate of the process
• After the testing process(1-3 months), the final version of the game (Gold
Master) is created
• The Gold Master is sent for replication, put in nice boxes and sent to
stores (about 2 weeks)
 Maintenance
• Support must be provided
 Patches, editing tools for the fan community, additional missions
• Networked games have a long, sometimes indefinite, maintenance time
Preproduction
■ Preproduction: Where Do Ideas Come From?
 A central idea of what the gameplay will be like
• Express in a single sentence that defines the genre and
gameplay as well as your role in the story
• Start with a strong narrative description
• Start with some unique and impressive technology
Preproduction
 Single sentence
• Your initial sentence must be answer
 Who is the player? |
 What’s the genre? |
What are his goals?
How does the game play?
• Ex) “The game is a first-person shooter, with some outdoors
area and large monsters, where you are a warrior trying to save
the princess”
 Narrative description
• Harder to code
• Ex) “Your are a scientist in a military complex full of soldiers
who are trying to conquer the world”
 Technology (more dangerous game type)
• The majority of your audience isn’t interested in technology
 Technology does not sell game or make them fun
• Ex) “Let’s build a game with this brand new outdoors renderer”
The safest bet is working from a core gameplay idea
and may be some narrative elements,
and discussing the best technological choice to convey the game world
Preproduction
■ Discussing Feature Sets
 Define a list of feature to be implemented into the game
 Expansion-contraction process
• Getting a reasonable feature set laid out on paper
• Expansion phase
 Every feature to be added to the game
 Put all your crazy ideas on a blank sheet of paper
• Contraction phase
 Review the list, merging those features that are similar
 Ex) “poisons” and “power-ups”  “items that affect the life
level”
• Review the result of the session
 Choose which clusters to implement
− Large clusters, small clusters, single features
Preproduction
 Minimax matrix
• A 2D matrix of cost versus benefit
• Minimize disadvantages and maximize advantages
 Advantages
− User-perceived value
− Generality
 Disadvantage
− Coding size
− Coding difficulty
Preproduction
 Minmax matrix (비용:이익)
• Minimin
 Features that are not important for the player but are easy to code
 They should be coded at the very end of the project
 Ex) birds flying by in a 3D adventure
• Maximin
 Features that offer little or no benefit in terms of the experience but are hard to
code
 They should be dropped immediately
 Ex) car racing game  see the driver inside the car
• Minimax
 Features that add a lot to the player‘s experience and are simple to code
 They should all be built into the game
 Ex) RPG game  configure the character’s look
• Maximax
 Features that define the gameplay experience and are hard to code
 Ex) flight simulation game  an outdoor renderer
 A Twofold analysis must be made
− Is there an easier implementation that convert a maximax feature into a
minimax feature?
− Is your team capable of handling the feature?
 Select some features and forget about the rest
Production
■ Production: Milestones Are King
 With all the core gameplay in place for your game prototype
 do’s and don’ts list
• More is not better
 “Emergency personnel” to help out
− Choose people who have all the information on the project
beforehand
• “On time: is better than “more ambitious”
 Sold per year sell at Christmas (50-60%)
 Try not to add new ideas to it in middle of the project
• Surgical teams and key members are a risk
 A key member left in the middle of the production??
• Order of execution
 Distinction between the core features and the accessories
 Useful to display the components to code and their order of
execution in a graph
Production
Production graph
Maintenance
■ Maintenance
 The goal of maintenance must be
• to maximize the enjoyment of the product by the consumer
• To make the life cycle as long as possible
 Some ideas taken from successful project
• Release new content for game
 Extra mission or characters
• Provide users with contents creation tools
 Make sure they are suitable for end users
− Using editor must be an enjoyable experience
 Ex) The Sims  tools to allow user-creation contents
• MMOG
 Keep a living community with ongoing activities
 A great time to organize, archive, and document