Unit 6 object-oriented simulation. Object-oriented simulation Used for simulation of physical systems Chemical plants Air combat Ecologies Key idea: the

unit 6

object-oriented simulation

Object-oriented simulation

Used for simulation of physical systems Chemical plants Air combat Ecologies

Key idea: the physical world consists of objects Objects have their own state Objects act on one another

Make a simulation which has one data object per physical object Give each object fields that mirror the state of the physical objects Give objects methods to implement the forces/actions that change

objects

Object-oriented programming

Means many things to many people

Least common denominator: Divide data into objects with fields Provide some mechanism to allow objects to specify their own methods

for implementing different procedures ( a.k.a. “messages”)

OOP with class-based inheritance Objects are divided into classes (types) Fields and methods determined are by an object’s class Subclasses inherit fields and methods from parent classes But can selectively override particular methods of the parent class

OOP in Meta [class [Name fields …]

Parent more-fields …] Creates a new class named Name With parent class Parent And fields fields … and more-fields …

[new Type args …] Makes a new object of type Type And sets its fields based on args

[define-method [initialize [Type arg]] Defines a method for initializing an

object of type Type before it’s returned by new

[generic-procedure] Makes a procedure that can be

specialized with methods

[define-method [generic [Type arg] …] body …]

Adds/modifies a method for generic procedure generic

Matches only those calls whose args have their corresponding Types

When a match is found, executes body

[call-next-method] When used inside a method, calls the

method of the parent class

Adventure games

One of the oldestcomputer game genres

Based on wandering through

a set of rooms interacting with

objects and characters Solving puzzles

or mysteries

Subgenres Point-and-click adventures (Myst, Syberia) Text adventure games (Zork, Infocom games) RPGs (Final Fantasy, Everquest, Baldur’s gate)

Ontology of adventure games

Game state: Spatiality

Things have locations (places) Places have contents (sets of things)

Inventory Equipment Consumables (health, gold, potions, etc.)

Key items “Unlock” parts of the game Allowing the narrative to progress

Things

Places

Persons

Player

NPCs

Monsters

Portals

Items

Key items

Supplies

Equipment

RoomsInventory

An adventure game in Meta

Supports Pictures (for point-and-click style) Text output Sound

You can decide which of these you want to use

Basic ontology Things (have name, location) Places (have name, contents) Player Portals (have name, location, destination)

The Thing class

Things have: Name

A string describing the object

May be null Location

Place in which the Thing can be found

May be null Adjectives

List of strings describing the object

May be null

[define Thing [class [Thing name location] Object adjectives]]

[define-method [initialize [Thing x]][move x x.location]]

The Place class

Places have Contents

A list of Things inside them Sound

Buffer to play when the user enters the room

Can be null if no sound Sound-loop?

If true, the sound plays continuously

Image Bitmap to display when the user

enters the room Hotspots

A list of places in the image the player can click and handlers (procedures to call) for when they’re clicked

[define Place [class [Place name] Thing contents hotspots sound sound-loop? image]]

[define-method [initialize [Place p]][call-next-method][p.contents ← [new ArrayList]]]

Trivial example

(Based on a randomly chosen picture from my hard drive)

One room Two Things in it

The Player A group of Nerds

Trivial example

[define trivial-example [→ [with great-hall = [new Place “the Great Hall”] [great-hall.adjectives ← [list “big” “pink”]] [great-hall.image ← [image-file “Aaron talk.jpg”]] [great-hall.sound ← [sound-file “dog-bark4.wav”]] [great-hall.hotspots ← [list [list 640 320 760 450 [→ [print “Aaron says Mythica was great until they killed the project.”]]]]] [the-player ← [new Player “Emily” great-hall]] [with nerds = [new Nerds null great-hall] [nerds.adjectives ← [list “many”]]] [start-game “Sample game” 800 600 100 100]]]]

Trivial example


Make the Place object

Trivial example


Set up its attributes

Trivial example


Make Player object

Trivial example


Make Nerds object

Trivial example


Open windowand start game

Moving objects

We need to make sure that If a thing T says place P is its

location Then P lists T in its contents And vice-versa

We make generic procedures for Adding and removing objects from

locations Moving objects between locations

This allows us to define special behavior for particular kinds of Places and Things

[define move [generic-procedure]][define remove [generic-procedure]][define add [generic-procedure]]

[define-method [move thing place][remove thing thing.location][add thing place]]

Adding and removing

Some Things can have null as their location

So we need to be careful to specialize the behavior of add and remove

Fortunately, you can specify null as the class of an argument

[define-method [remove thing [null place]]«Do nothing»null]

[define-method [remove thing [Place place]][thing.location ← null][place.contents.Remove thing]]

[define-method [add thing [null place]][thing.location ← null]]

[define-method [add thing [Place place]][thing.location ← place][place.contents.Add thing]]

Describing objects For text adventures

We need a way to generatetext to describe objects

We want to base it on The name of the object (if any) It’s type Its adjectives (if any)

Examples [description [new Cat]]

“a cat” [description [new Cat “Harry” null]]

“a cat named Harry” [with h = [new Cat “Harry” null]

[h.adjectives ← [list “big” “black”]] [describe h]]

“a big, black cat named Harry” Notes

Concat is a procedure that appends strings together Stuff in gray is black magic we haven’t taught you about yet

[define description “Returns a string describing the object”[generic-procedure]]

[define-method [description [Thing t]][with type-name = [[type-of t].Name.ToLower] modifiers = [maybe-pad [comma-separate t.adjectives false]] name-string = [if [null? t.name] “” [concat “ named ” t.name]] [concat “a ” modifiers type-name name-string]]]

Describing scenes

[define-method [view-description [Place p]][with stuff = [filter [t → [≠ t the-player]] «Everything in the room except the player» p.contents] [concat “You are in ” [description p] “. ” [cond [[= [length stuff] 1] [concat “You see ” [description [first stuff]] “.”]] [[empty? stuff] “”] [else [concat “ You see ” [comma-separate [map description stuff] true] “.”]]]]]]

Describing scenes

[describe great-hall]

“You are in a big, pink place named the Great Hall. You see a many nerds.”

Choosing the sound to play

[define background-sound “Returns the sound buffer for the background noise of this Place, if any”

[generic-procedure]]

[define-method [background-sound [Place p]]p.sound]

The window code calls background-sound on the player’s location to choose what sound to play

Why did we do it this way? Why not just have it play p.sound directly?

Choosing the image to show

[define view-image [generic-procedure]]

[define-method [view-image [Place p]]p.image]

Again: why bother with a procedure like this?

Handling clicks of the mouse The hotspots of a Place is a field

with a list of lists: [list left top

right bottom proc]

Where: Left and top give the

coordinates of the upper-left corner of an area of the image

Right and bottom give the coordinates of its lower-right corner

Proc gives a procedure to call when the user clicks there

But again, you can change the behavior of clicking by

Making a new kind of place (i.e. a subclass of Place)

and defining a new method for it

[define click [generic-procedure]]

[define-method [click [Place p] mouseEventArgs][with x = mouseEventArgs.X y = mouseEventArgs.Y [unless [null? p.hotspots] [for-each [hotspot → [when [and [≥ x [first hotspot]] [≥ y [second hotspot]] [≤ x [third hotspot]] [≤ y [fourth hotspot]]] [[fifth hotspot]]]] p.hotspots]]]]

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Unit 6 object-oriented simulation. Object-oriented simulation Used for simulation of physical systems Chemical plants Air combat Ecologies Key idea: the