Table of Contents

Scrolling, Sound, AI

Scrolling, Sound, AI

Scrolling Games

Example: Super Mario Brothers
- Game that travels left or right well beyond the length of the game panel
Graphics requirement: tile maps (a.k.a., “bricklaying”)
Backgrounds are often composed of several tile map layers
Scrolling Demo:
- The following example illustrates a wrap-around “ribbon” background.
- ScrollDemo.java (main program)
- ScrollPanel.java
- Ribbon.java
- mario-1-1.gif

Sound Basics

Two types of sound used in games
- Sampled audio data - Series of digital values that represent the amplitude or intensity of sound pressure waves
  - Most often used for game feedback (i.e. audio effects)
  - Support for encoded/compressed audio (e.g. mp3) is also used in games.
- Synthesized audio data
  - Example: MIDI (Musical Instrument Digital Interface) - A standard electronics communications protocol
    - used in a many video games (in almost all NES games)
  - Most often used for game atmosphere (i.e. background music)

Playing a Sound in Java

Java Sound API

Allows access to (and manipulation of) audio data and the underlying machine's audio hardware and software
The packages: (SoundPlayback.java)
- javax.sound.sampled.*
  - Handles digital audio data
    - Supports WAV, AU, and AIFF formats, and can be extended to support more formats such as mp3
  - Going beyond simple sound playback:
    - Port - I/O to microphone, speaker, etc.
    - Mixer - Audio device with multiple I/O lines
    - DataLine - Adds functionality to a line, including start, stop, and pause audio.
    - GainControl - Used to manipulate an audio signal's volume
    - PanControl - Used to control the balance between the left and right stereo channels

Example: Simple sound recording application with playback

Game AI

What is AI?
- The study of computational systems that “exhibit intelligence”
- Capabilities: problem solving, planning, and learning

“AI” in Games (note the double quotes)
- Opponents (e.g., how can they outsmart you?)
- Computer teammates
- Support characters and autonomous characters (NPCs - non-player characters)
- Commentators (sports games)
- Camera control
- Plot control (story branching)
- Some goals of AI in games:
  - Provide challenging opponents…
    - …but not too challenging or too predictable
  - Gather enough knowledge…
    - …but aim for low CPU and memory usage
  - Provide an illusion of reality (e.g., human characteristics)

Experiences with game AI? Game-generated opponents that you thought were well done?

Effects of Bad AI
- Reduced fun
- Extreme behaviors (from lame to superhuman)
- Unrealistic behaviors
- Mindless hordes (of opponents)
- Cheating

Sample Problems for a game AI
- What to do when the enemy is heard or sensed?
- What to do when AI-controlled character health level is low?
- What to do if AI-controlled character doesn't see or hear anything? (idle time)
- How to move from point A to the goal in a maze?
- How to move a flock of objects (e.g., birds)?

Building a game AI agent
- Given: the environment
- Cycle (one iteration of the game loop):
  - Sense - Gather information about the environment
  - Think - Use some decision-making routine
  - Act - Execute something based on the decision
  - Repeat steps
- Some constraints:
  - Memory: What to remember and for how long?
  - CPU usage

Finite State Machines (FSM)

Glossary:
- FSM - A collection of states and transitions that outline a path of actions that may occur.
- State - A state is a position in time.
  - For example, when you are at the bus stop, you are currently in a waiting state.
- Event - An event is something that happens in time.
  - For example, the bus has arrived.
- Action - A task performed given a certain event that occurred.
  - For example, you enter the bus.
- Transition - A link between 2 states.
  - May be unidirectional or bidirectional.

Possibly the simplest type of game AI decision-making engine
Looks like the state diagrams in game design documents
- Also see http://www.generation5.org/content/2003/FSM_Tutorial.asp
Strengths:
- Simple, quick
- Can be compacted into a simple data structure such as an array

Finite State Machine Example: Quake II
- 9 different states for AI-controlled enemies
  - Standing
  - Walking
  - Running
  - Dodging
  - Attaching
  - Melee
  - See the enemy
  - Idle
  - Searching

References