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unit 7. more on the adventure game. The code is divided into several files It is distributed as a .zip file Download it from the web Unzip it into the directory of your choice To load the code Click the file “Adventure.meta” Choose Execute All from the Execute menu.

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unit 7

unit 7

more on the adventure game

working with the code
The code is divided into several files

It is distributed as a .zip file

Download it from the web

Unzip it into the directory of your choice

To load the code

Click the file “Adventure.meta”

Choose Execute All from the Execute menu

The list of files is stored in the variable source-files in Adventure.meta

To add a new file

Add its name to the end of source-files

Type Control-E to update the definition

Run: [reload]

Working with the code
a tour of the code

List of source files

Code to load other source files

Code to find art assets (sound and image files)


Basic code for handling text input

Basic class files

Things.meta, Places.meta, Actors.meta, Player.meta, Portals.meta

Sound stuff.meta

OS-dependent code for loading and playing .wav files

User interface.meta

OS-dependent code for window updating, and handling of user events (clicks and text input)

String utilities.meta

Stuff for handling text

Sample game.meta

Example game

A tour of the code

You only need to worry about the basic class files and the sample game

  • Sounds
    • Holds any sound files you want (.wav only, sorry)
    • Files can be accessed using the [sound-file filename] procedure
  • Images
    • Holds any images files (.jpg, .gif, .bmp, or .png) you want to use
    • Files can be accessed using the [image-file filename] procedure


    • You don’t have to include the directory names in the filenames for sound-file and image-file. They know to search in the Sounds and Images directories, respectively.
recap 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


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


When used inside a method, calls the method of the parent class

Recap: OOP in Meta
an adventure game in meta
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:


A string describing the object

May be null


Place in which the Thing can be found

May be null


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 Thing class
the place class
Places have

ContentsA list of Things inside them


Buffer to play when the user enters the room

Can be null if no sound


If true, the sound plays continuously


Bitmap to display when the user enters the room


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]]]

The Place class
update handling clicks of the mouse
We’ve made definition of click actions more versatile since the last lecture

The hotspots of a Place is a field with a list of lists:

[list left top right bottom handler]


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

handler is either a procedure to call or a game object such as a place

If it’s a procedure, the system calls it

If it’s a string, the system prints it

If it’s a place, the system moves the user there

If it’s any other game object, it runs click on 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]]] [click [fifth hotspot]]]] p.hotspots]]]]

[define-method [click [Place p]][move the-player p]true] «Returning true tells the system to update the image, replay the sound, and generate new text»

[define-method [click [String s]][print-line s]false] «Returning false means don’t redraw anything»

[define-method [click [Procedure p]][p]]

Update:Handling clicks of the mouse
the portal class
Portals are objects that, when clicked on, move the player to a specified destination

However, it looks funny for the system to print “You see a portal”

So there’s a subclass called “Door”

[define Portal[class [Portal name location destination] Thing]]

[define Door[class [Door name location destination] Portal]]

[define-method [click [Portal p]][move the-player p.destination]true]

The Portal class
handling text input
[define-pattern procedurepattern …]

Tells the system to run procedure when the user types something that looks like pattern…

Elements of pattern can be:

Strings (must be matched exactly)

Type names

String (the type)Matches whatever the next word is

Thing, Place, etc.System searches the user’s current location for an object of this type

[define quit [→ [current-window.Close] false]]

[define-pattern quit “quit”]

Tells the system to run the quit procedure when the player types “quit”

Handling text input
a fancier example
This example sets the variable mouse-debug-mode?

To true when the user types “mouse debug on”

Or false if they type “mouse debug off”

When mouse-debug-mode? is true

The system prints the image coordinates of the point you click on

Rather than running the click procedure

This lets you easily find coordinates when you’re making hotspots in your images

[define set-mouse-mode [mode → [mouse-debug-mode? ← [≠ mode “off”]] [print-line [if mouse-debug-mode?“Mouse hits will display coordinates”“Mouse hits will call click methods”]] false]]

[define-pattern set-mouse-mode“mouse” “debug” String]

A fancier example
other built in handlers
Other built-in handlers
  • “debug [on/off]”
    • Turns the variable debug-mode? true or false
    • Not used by the system but might be useful for you.
  • “go back”
    • Brings the user to the place they were last
a more interesting example
Typing “go to” and a Portal clicks the Portal (which moves the user to the portal’s destination)

You can define behavior for going to other kinds of things by writing methods for the goto procedure.

[define goto [generic-procedure]]

[define-method [goto [Thing p]]«Nothing happens»false]

[define-method [goto [Portal p]][click p]]

[define-pattern goto“go” “to” Thing]

[define-pattern goto “go” Thing]

A more interesting example
the sample game
Brief highlights of my trip to AAAI last year

AAAI is an Artificial Intelligence Conference

Yes, I know this is a lame example

To run it:

Load: Sample game.meta

Run [sample-game]

[define great-hall null]

[define robot-room null]

[define art-room null]

[define origami-room null]

[define sample-game[→ [great-hall ← [new Place “the Video Games Symposium”]] [robot-room ← [new Place “the robot area”]] [art-room ← [new Place “the art installation”]] [origami-room ← [new Place null]] [set-up-hall] [set-up-robot-room] [set-up-art] [set-up-doors] [start-game “Sample game”

800 600 100 100]]]

The sample game
example room the great hall
It’s best to write a separate procedure to initialize each room

That keeps the top-level procedure from being too big and hard to read

Set up sound and image

Set misc-text field

Which we didn’t talk about, but which prints when you enter the room

Set hotspots to various strings and procedures to run

Make the player

And put it in the magic variable the-player

Make the nerds

[define set-up-hall[→ «Set up the great hall» [great-hall.image ← [image-file “Aaron talk.jpg”]] [great-hall.sound ← [sound-file “clap.wav”]] [great-hall.misc-text ← “Aaron Khoo is giving a talk on Mythica.”] [great-hall.hotspots ← [list [list 174 392 238 471 ouch] [list 466 346 585 451 ouch] [list 46 87 513 440 “Stop that. You'll get finger prints on it.”] [list 640 320 760 450“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”]]]]]

Example room: the great hall
the ouch procedure
The ouch procedure

[define ouch-counter 0]

[define ouch-statements[list “Ouch” “Please don't do that.” “Ouch!” “Are you having a good time?” “This is getting a little infantile, isn't it?”]]

[define ouch [→ [print-line [get ouch-statements ouch-counter]] [when [< ouch-counter [− [length ouch-statements] 1]] [ouch-counter ← [+ ouch-counter 1]]]]]

the eat procedure
Lets you type “Eat [Thing]”

Simulates destroying the Thing by moving it to null (i.e. nowhere)

Now it’s not in the room

And so it appears to be destroyed

Prints “Mmmm, yumming Things …”

Returns false

Which tells the system not to redraw the display

[define eat[thing → [move thing null] [print-line “Mmmm, yummy ”[[type-of thing].Name.ToLower] “...”] false]]

[define-pattern eat“eat” Thing]

The Eat procedure
the art and origami rooms
The art room brings you to the origami room when you click on it

[define set-up-art[→ «Set up the art room» [art-room.image ← [image-file “Art installation.JPG”]] [art-room.misc-text ← “It was make by art and robotics students from the University of New Orleans.”] [art-room.hotspots ← [list [list 130 50 323 360 origami-room]]]

«Set up the origami room» [origami-room.image ← [image-file “Origami room.jpg”]] [origami-room.sound ← [sound-file “dog-bark4.wav”]] [origami-room.adjectives ← [list “origami filled”]]]]

The art and origami rooms
making doors
Doors in this system are only one-way

They live in one room

And lead to the other

But aren’t visible in the other

So we need to make doors in pairs

One from room A to room B

One from room B to room A

So it’s easiest to make a procedure to do this for us

[define make-door-pair[place1 name1 place2 name2 → [new Door name1 place1 place2] [new Door name2 place2 place1]]]

[define set-up-doors[→ «Connect the rooms» [make-door-pair great-hall null robot-room “symposium”]

[make-door-pair art-room null robot-room “art”]]]

Making doors