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GAM 200 Club
How to Game EngineGAM 200 ClubZachary Nawar
DISCLAIMERThere are many methods and ways of going
about and creating a Game Engine, this is a very simple yet useful method for starting to build
your engine
Step 1: Object Architecture
Inheritance based VS Component based• Very generic base
object• Each object inherits• Tons of abstract objects• Simple and easy• UE3 is a great example
• One object class• Components add
logic• Faster iteration• More complicated to
do
Step 2: Object Management
Decide on what method to use for object management:
> Single Game SpaceEach object exists in the same “space” or
collection of objects> Multiple Game Spaces
Multiple “spaces” which contain their own sets of objects
Now to build our Engine
I build from small to large
When declaring and defining your functions imagine what you want the end user (Your team) to experience when
they try to do things in your engine
Engine / Game Space / Game Object
Step 3: The (Base) Component
Base Component has very basic stuff!• Constructor / Destructor• Initialize / Update / Remove functions• ptr to the owning Space (optional)• ptr to the owning Object• TypeID (enum, int, const char*, you choose!)
Keep it simple, clean, and virtualReal components inherit from this
Step 4: The Game Object
What put inside?• Constructor / Destructor• Initialize / AddComponent / GetComponent /
Update / Remove functions• Array of Component pointers• Global ID (?)• More complicated things*
• Object Parenting info• Archetype names
Step 5: The Game Space
Think of it as an object manager• Constructor / Destructor• Update function• Array of Objects pointers• Other helper functions
• Cleanup, Clear, AddObject
Step 6: The Engine Core
• The core of your entire engine• Home to your Init, AddSystem, Loop, Shutdown
• No need to implement these just yet• Stores all of your Game Spaces
• Array of pre-allocated spaces?• Array of pointers?
• Pointer to additional Systems• Make a global pointer to your Core
We have now achieved our desired structure
Step 7: The “Object Factory”
We need a way to make Objects!• Our “Object Factory” does exactly this• Could be a class full of static functions
• Just have the first parameter take a GameSpace*
• CreateObject()• Allocates space for an object• Adds object to game space• Returns the new object
Step 7.1: Serialization
The Factory is a great place to load objects
• Allocate object• Load file• File says what components to add to object• File says what to set variables in components to• Add object to game space• Return the object (No need to really)
Data driven! yay!CS225 should cover JSON serialization
• Also could be covered in future presentation
Making Objects in C++
Step 8: Engine Systems
Currently all we have is an object engineWe should add features to our engine!
• Graphics, Physics, Audio, GameLogicI call these “Systems” or “Modules”
• Expand and provide functionality to the engine
• Makes our Game Engine capable of running games
Step 8.1: Base Engine System
This is the base/generic system• Constructor / Destructor• Init / Update / Shutdown functions• Name (optional)
Remember to keep it virtualEvery system we add (Graphics, Physics…) inherits from this basic system
Step 8 Example
Graphics SystemSetTransform(MATRIX33 m) // Sets matrix to use when drawingSetDrawMode(DMODE_ENUM dm) // Sets draw modeSetTexture(D3DTexture tex) // Sets the texture to drawDrawSprite() // Draws a sprite using transform, drawmode, textureStartFrame() // Starts a frameEndFrame() // Ends the current frame, swaps buffersUpdate() // Iterate through spaces/objects/components call Draw if
we can?
Step 9: Back to the Engine Core
Implement those engine functions!• AddSystems• Initialize• Loop
Step 9.1: AddSystem
void Core::AddSystem(ISystem* sys)Responsible for adding a system pointer into the Engine Core list of systems
Push pointer into back of system pointer array/vector
Step 9.2: Init
void Core::Init(void)Responsible for Initializing all engine systems
Iterate through each System in array of SystemsCall Init function
Step 9.3: Loop / MainLoop / Updatevoid Core::Loop(void)Responsible for keeping the game running, the game loop● While RUNNING
○ If Framerate controller says go■Iterate through systems in systems list
●Call Update function
Something that’s missing: GameLogic
GameLogic can/should be a system too• Iterates through all game spaces
• Update Game Space• Iterate through all Objects
• Update Object• Iterate through all Components
• Update Component
This method is simple and works
Invoking our Engine
1. Create Engine Core2. Create and add engine systems3. Initialize Engine Core4. Load a game level or something5. Call Loop function6. Call Shutdown function7. Exit program
Things to work on next:
• Handle manager• Messaging (Hooks, Events, ect.)• Cache friendly memory management• Archetypes• Saving and Loading levels• Introspection and Serialization• Scripting languages