Score, Variables, Conditionals in
Game Maker (BrickMania 2 of 2)
Foundations of Interactive Game Design
Professor Jim Whitehead
January 30, 2008
Creative Commons
Attribution 3.0
creativecommons.org/licenses/by/3.0
Announcements
• www.soe.ucsc.edu/classes/cmps080k/Winter08/
Has syllabus, assignment descriptions, exam days, final
exam time, link to gamelog site, links to tool descriptions,
and more…
• Game club announcement
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Meet Thursdays, 2:15pm
Conference room A
• Go in entrance next to “Express It”
• Help for making your Mac dual boot:
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Contact Ian Rickard to arrange help time
• [email protected]
Game Design Workshops
• Game Maker
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Wednesdays (starting today)
6-8pm
Engineering 2, room 180 (Simularium)
• Enter on plaza level between E2 and JBE
• RPG Maker
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Wednesdays (starting today)
5-7:15pm
Engineering 2, room 280
• 2nd floor, on front of building, on driving circle/Communications
end (right side, east end) of the building
• Arrive by 6pm to avoid external doors locking
• Knock on nearest door to be let in if late…
Game Design Workshops
• CS 20/C# and XNA Game Studio Express
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Thursdays, 4:30-7pm
Engineering 2, room 399 (third floor, by elevators)
Starts this week
Upcoming Exams and Assignments
• Exam #1: Friday, January 26
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Will cover all material in lectures
Material from readings also fair game,
even if not covered in lecture
Will give a list of study questions today
Closed book, closed note
Bring pencil/pen
Arrive early, seating will be tight
Potential Exam Topics
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As Univ. of California students, you are expected to be
able to assess complex material and make judgments
concerning its relative importance.
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That said, it can be helpful to have some input from the
Professor to help focus studying activity.
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The following are questions/material that are likely, but not
guaranteed to appear on the exam.
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Anything covered in class or in
the assigned readings may appear,
even if not explicitly mentioned today.
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Exception: Test will not cover new
material covered in today’s class
Potential Exam Topics (2)
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Rules, play, culture framework
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Difference between games, toys, play
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Given an activity, be able to describe why it is a game, toy, or play
Know Abt, Costikyan, and Juul game definitions
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Know both the definitions, as well as differences among them
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Understand all six elements of Juul’s definition
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Know what each category represents
Given a game, be able to describe elements of the game that
match rules, play, & culture
Be able to describe whether an activity is a game according to
each definition
Know Huizinga and Caillois definitions of play
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Understand differences between them
Know six elements of Caillois definition
Potential Exam Topics (3)
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Know the concept of the magic circle
Understand the dichotomy of rules as limitations and
rules as affordances
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Describe how game rules create the structure of a game
Know the seven aspects (qualities) of rules
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Know what an affordance is (p. 57-58 of Juul)
On p. 55-56 of Juul
Understand the difference between operational,
constituative, and implicit rules
Understand the concept of a finite state machine
Describe the difference between games of emergence
and games of progression
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Be able to place a game in one or the other category
Know the game guide test of progression and emergence (p. 71
Juul)
Potential Exam Topics (4)
• Game Maker
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Know difference between Sprite and Object
Know difference between Event and Action
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Know that events are received by objects, who take action
based on them
Know what a Room is, and what it can be used for
• Know that a room contains objects and backgrounds
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Know what a Background is
Understand the benefit of inheriting behavior from a
parent object
• CS 20 students are expected to answer Game
Maker questions
Potential Exam Topics (5)
• Understand difference between gameplay rules
and gameworld rules
• Temporal aspects of games
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Know cardinality of gameplay
Different types of game exhaustion
Know concept of segmentation of gameplay
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Also know different kinds of segmentation (challenge, spatial,
temporal, narrative)
Should understand that Conway’s game of Life is:
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from Milton Bradley game of Life
► Example of emergent behavior from a simple rule set
CS 20: Potential Exam Topics
• Given an example of C# code, should be able to identify
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Array, property, loop constructs, class definition, method definition,
variable definition
• Understand meaning of private, protected, public
• Given a simple example of C# code, should be able to
provide its output
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Including switch, conditionals, properties, foreach, lists, etc.
• Should be able to write simple get and set accessor code
to create a property
• Should be able to write a simple foreach loop
• Know difference between value and reference types
Let’s create a simple Breakout game
• Game elements
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Background
Ball
Paddle
Score
Lives
3 brick types
Playfield is
smaller than
screen
Score System
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Game Maker has a special system for maintaining score
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Can think of it as a global “score” variable
Use Set Score on score tab
Typically with a “relative” value to add to current score
• Below, if “relative” not clicked, would reset score to 10, instead of adding 10
Displaying Score & Draw Events
• Want to display score in lower left corner
• Game Maker has a “Draw the Value of Score”
action
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But, it can only be used inside a Draw Event
• Draw Event
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Typically, in each step Game Maker draws the sprite for
an object on screen
Using a Draw Event, you can specify a different set of
drawing commands
• Could, for example, draw a halo around your sprite
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Draw Event also used for utility drawing behavior
• Such as displaying the high score
Create Game State object
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To display the current score, want an object that is invisible
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So its sprite isn’t affected by score drawing
Create a “game state” object
Also useful
No sprite - invisible
for holding
number of lives
Place in room
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Location doesn’t
matter, is invisible
Draw event
Set color to
white (for
white on
black text)
Draw score in
lower left of
screen
Desired Lives Behavior
• Player has 3 lives
• When ball goes offscreen below paddle, need to
subtract one life
• Want a nice display of remaining lives
• When there are no more lives, display a game
over message
Lives System
• Game Maker has a built-in lives system
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Similar to score, a built-in global variable
Can set number of lives, check number of lives
Draw a representation of number of lives
• Uses an existing sprite to represent a life
• General idea: hearts representing life in Zelda series
Displaying Lives
• Select “Draw Life Images” and place inside a Draw Event
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Place in Draw Event in Game State object
• Has no sprite, don’t need to worry about effect on object’s normal
sprite drawing
Pick sprite to use for life image
(small paddle image)
Place in absolute
position on screen
(upper left)
Set Initial Lives
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Need to set the initial number of lives
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Do this in create event on game state object
We do not want to do this on the paddle object
• Will be destroying paddle object instances when the ball goes offscreen
• Then re-creating paddle for a new ball
• Setting lives in the create event on the paddle would cause the lives to be reset
to the starting amount each time a ball was lost
Ball Going Offscreen
• When ball goes offscreen below paddle
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Sound effect
Decrease lives by one
• If no more lives, display “Game Over”
• Then, press key to restart game
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Visually remove paddle
Pause game
Create new paddle
Create new ball
Set ball moving
• Check for this by putting a conditional (if … then) in the
End Step event
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I.e., check ball’s position every clock tick to ensure is still in-bounds
Variables
• Variable
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A named value
Can be read: look up the value
Can be written: change the value to something new
• Examples
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The horizontal location of the player in the room is
named “x”
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The vertical location of the player in the room is named
“y”
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Its value is a number between 0 and the width of the room
Its value is a number between 0 and the height of the room
Need names to identify the value we want
Variables (2)
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Full disclosure
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There appear to be two kinds of variables
Variables defined on object instances
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Global variables
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x and y giving player position are defined on the player object instance
Most of the dialog boxes in Game Maker default to instance variables,
so don’t have to worry about this point usually
We’ll see these in a few slides, things like view information
Seem to be able to access these anywhere
In Game Maker
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Can set the value of a variable using square “Var” action
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Under “Control” tab in Object window
That is, setting a variable is a kind of action
– Set a variable in response to an event
Conditionals
• If .. then behavior
• Example
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If the player horizontal position is outside the view...
Then make sure the player stays inside the view
• Conditionals in Game Maker are represented by
octagon shapes
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Found under “Control” tab
Are an action you can take in response to an event
• Often want to check condition all the time
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Place these in the step event
Step event is called every game tick (1/30th of a
second)
Ball Going Offscreen Logic
Conditional:
if y > 480 then…
Play sound,
remove paddle,
decrease lives,
and sleep
Lives < 1 means
game over.
Create game over
message. Destroy
ball.
Still have lives.
Create new
paddle. Move ball
to starting
position. Make
ball move up and
diagonally.
Control Tab
Conditional Dialog Box
Can check the value of a variable on
yourself, or on the other object in a
collision, or on any arbitrary object
Choices are:
larger than
equals
less than
Missing from the Game
• The game still needs end-screen logic
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Need to count number of bricks
When all are gone, go to next screen
• Could redraw the same screen
• Could create a new room with a new arrangement of bricks
• Power-ups
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Could have many interesting powerups
Multi-ball, bigger paddle, etc.