CSCE 552 Spring 2009

Programming Fundamentals

By Jijun Tang

Homework #1

6 points, due on next Wednesday Turn in hard copy before the class Expected about 1 page Question: Review your popular games

(2-3), including game description, features, strength and weakness, etc.

C++: Strengths

Performance High-level, object-oriented C Heritage Libraries

C++: Weaknesses

Too low-level Slow iteration Too complicated Lacking features

Java Performance

Has typically been Java's weak point Has improved in the last few years: still

not up to C++ level, but very close Uses Just-In-Time compiling and

HotSpot optimizations Now has high-performance libraries Also has access to native functionality

Popular scripting languages

Python Lua Other off-the-shelf options such as

Ruby, Perl, Javascript Custom scripting languages

UnrealScript, QuakeC, NWNScript

Data Structures: Array

Elements are adjacent in memory (great cache consistency) Requires continuous memory space

They never grow or get reallocated Use dynamic incremental array concept GCC has a remalloc function

In C++ there's no check for going out of bounds Use vector if possible Keep in mind of checking boundaries

Inserting and deleting elements in the middle is expensive

List

Very cheap to add/remove elements. Available in the STL (std::list) Every element is allocated separately,

not placed contiguously in memory Lots of little allocations Bad cache awareness, but can use arrays

to hold pre-allocated items Single/Double linked list

Lists

Dictionaries

Maps a set of keys to some data. std::map, std::hash, etc Very fast access to data Perfect for mapping IDs to pointers, or

resource handles to objects May waste space, need to design

comparison operators

Hash Table

Others

Stacks First in, last out std::stack adaptor in STL

Queues First in, first out std::deque Priority queue is useful in game to schedule

events

Stack/Queue/Priority Queue

Bit packing

Fold all necessary data into a smaller number of bits

Bool in C++ may use up to 4 bytes, thus is very expensive

Very useful for storing boolean flags: pack 32 in an integer

Possible to apply to numerical values if we can give up range or accuracy

Very low level trick Use shifts to handle the operation or use assembly Only use when absolutely necessary

Bits

Game Architecture and Math

Inheritance

Models “is-a” relationship Extends behavior of existing classes by

making minor changes Do not overuse, if possible, use component

systerm UML diagram representing inheritance

E ne m y B o s s Supe rD upe rB o s s

Polymorphism

The ability to refer to an object through a reference (or pointer) of the type of a parent class

Key concept of object oriented design C++ implements it using virtual functions

Multiple Inheritance

Allows a class to have more than one base class

Derived class adopts characteristics of all parent classes

Huge potential for problems (clashes, casting, dreaded diamond, etc)

Multiple inheritance of abstract interfaces is much less error prone (virtual inheritance)

Java has no multiple inheritance

Dreaded Diamond

It is an ambiguity that arises when two classes B and C inherit from A, and class D inherits from both B and C.

If a method in D calls a method defined in A (and does not override the method), and B and C have overridden that method differently, then from which class does it inherit: B, or C?

Component Systems

Component system organization

G am e E nti ty

N am e = s w o r d

R e nde rC o m p C o ll is io nC o m p D am age C o m p P ic kupC o m p W ie ldC o m p

Object Factory

Creates objects by name Pluggable factory allows for new object

types to be registered at runtime Extremely useful in game development

for passing messages, creating new objects, loading games, or instantiating new content after game ships

Factory Pattern

Simple Sample Factory - I

Simple Sample Factory - II

Singleton

Implements a single instance of a class with global point of creation and access

For example, GUI Don't overuse it!!!

Single to ns ta tic S in g le to n & G etI n s tan c e ( ) ;/ / R eg u lar m em b er f u n c tio n s . . .

s ta t ic S in g le to n u n iq u eI n s tan c e ;

Singleton Example

Adapter

Convert the interface of a class into another interface clients expect.

Adapter lets classes work together that couldn't otherwise because of incompatible interfaces

Real interface

Adapter Pattern

Adapter Example - I

Adapter Example - II

Observer

Allows objects to be notified of specific events with minimal coupling to the source of the event

Two parts subject and observer

Observer Pattern

Composite

Allow a group of objects to be treated as a single object

Very useful for GUI elements, hierarchical objects, inventory systems, etc

Composite Pattern

Composite Pattern Example - I

Add many more inherited classes

The Five StepDebugging Process

1. Reproduce the problem consistently

2. Collect clues

3. Pinpoint the error

4. Repair the problem

5. Test the solution

Expert Debugging Tips

Question assumptions Minimize interactions and interference Minimize randomness Break complex calculations into steps Check boundary conditions, use assertions Disrupt parallel computations Exploit tools in the debugger (VC is good, purify) Check code that has recently changed Explain the bug to someone else Debug with a partner (A second pair of eyes) Take a break from the problem Get outside help (call people)

Game Architecture

Overall Architecture

The code for modern games is highly complex The Sims: 3 million lines of code Xbox HD DVD player: 4.7 million lines MS Train Simulator has 1GB installed, with only

10MB executable With code bases exceeding a million lines of

code, a well-defined architecture is essential

Overall Architecture

Main structure Game-specific code Game-engine code

Both types of code are often split into modules, which can be static libraries, DLLs, or just subdirectories

Overall Architecture

Architecture types Ad-hoc (everything accesses everything) Modular DAG (directed acyclic graph) Layered

Options for integrating tools into the architecture Separate code bases (if there's no need to share

functionality) Partial use of game-engine functionality Full integration

Ad-hoc

Modular

DAG

Layered

Overview: Initialization/Shutdown

The initialization step prepares everything that is necessary to start a part of the game

The shutdown step undoes everything the initialization step did, but in reverse order

Initialization/Shutdown

Resource Acquisition Is Initialization A useful rule to minimalize mismatch errors in the

initialization and shutdown steps Means that creating an object acquires and

initializes all the necessary resources, and destroying it destroys and shuts down all those resources

Optimizations Fast shutdown Warm reboot

Overview:Main Game Loop

Games are driven by a game loop that performs a series of tasks every frame

Some games have separate loops for the front and the game itself

Other games have a unified main loop Must finish a loop within 0.017 second

Tasks of Main Game Loop

Handling time Gathering player input Networking Simulation Collision detection and response Object updates Rendering Other miscellaneous tasks

Sample Game Loop

Main Game Loop

Structure Hard-coded loops Multiple game loops: for each major game state Consider steps as tasks to be iterated through

Coupling Can decouple the rendering step from simulation

and update steps Results in higher frame rate, smoother animation,

and greater responsiveness Implementation is tricky and can be error-prone

Execution Order of Main Loop

Most of the time it doesn't matter In some situations, execution order is

important Can help keep player interaction

seamless Can maximize parallelism Exact ordering depends on hardware