Shooters in GameMaker
J Parker
Scrolling Shooter
In a scrolling shooter the player controls an object,
for example a plane, spaceship, or car, which
moves over a scrolling background.
Obstacles appear on the background that must be
avoided and enemies appear that must be shot.
Often bonus objects appear that can be picked up
for addition benefits.
Examples: Space invaders, Galaxian
1945
The player flies in a plane over a sea and enemy
planes try to destroy the player.
Variable
A new concept in GameMaker, a variable is a
property of an object that can be changed.
- The position of an object has an X and Y value
- The speed of an object has a horizontal and a
vertical part
- The score is a variable
- The height and width of the room are
variables
Etc etc etc
Variable
A variable can be used to save an important
value for later use (EG position of an enemy)
A variable can represent a property of an object
that is important and needs to be used by the
game.
A variable can be modified by the game, thus
modifying how the corresponding object
looks and behaves (EG change object’s speed)
Variable
Changing a variable’s value is done as follows:
On the CONTROL tab find
Testing a value uses the
button.
Setting a variable
Testing a variable
1945 Design
• Description
• In this game you control a plane flying over a
sea. You encounter an increasing number of
enemy planes that try to destroy you. You should
avoid these or shoot them. The goal is to stay
alive as long as you can and to destroy as many
enemy planes as you can.
Game objects
The background is formed by a scrolling sea with
some islands. The player’s plane flies over this
1945
Game objects
The background is formed by a scrolling sea
with some islands. The player’s plane flies
over this sea. You can shoot bullets that
destroy enemy planes. There are four types of
enemy planes: a plane that you encounter
and should be destroyed, a plane that fires
bullets downwards, a plane that fires bullets
towards the player’s plane, and a fast enemy
plane that comes from behind rather than
from the front.
1945
Sounds
There are some explosion sounds and there is
some background music.
Controls
The player controls the game with the arrow
keys. With the space key you fire a bullet.
Only one bullet can be fired every five steps.
1945
Game flow
The player immediately jumps into the game.
The player has three lives. When all lives are
gone a high-score table is shown. Pressing the
<F1> (help) key will give a brief explanation.
Pressing the <Esc> key will end the game.
Levels
There is just one level, but more and more
enemy planes will arrive: first only the easy
type but later the more difficult types.
Motion – An Illusion
There are two possibilities for creating the motion
illusion:
• use a tiling background image that moves
downwards through the room.
• build a much larger room but only show part of
the room using a so-called view. This view slowly
moves upwards over the room.
We will use a moving background.
Water
We need a background image that looks like a
sea viewed from above.
We add the following small image as a
background resource to the game and give it
the name back_water:
Filling the background with it will give a nice
looking sea.
Water
In a scroller, the background image should
move.
To create a room with a moving background,
add a room to the game in the familiar way.
At the left click on the tab labeled
backgrounds. We need to change three
settings here.
1. First of all, because we are going to fill the
whole room with the background image, so
uncheck the box labeled Draw background
color.
Water
Second, in the middle click on the menu icon
and select the back_water background
image. The default setting is to tile the whole
room with it so this is what we want.
Finally, we need to make the background move.
To this end, at the bottom, set the Vert.
speed to 2.
Now try it.
Motion, water, islands, ...
• To enhance the feeling of motion we are
going to add a few islands to the sea.
• An easy way would be to create a larger
background image and add the island to this
background. Iislands will appear in a regular
pattern, which the player soon notices. (Bug
Bunny) So we choose a slightly more
complicated approach and add the islands as
objects.
Motion, water, islands, ...
Create three sprites with the following images
We will never use them for collision checking so
uncheck the box Precise collision checking.
For each of the islands we create an object.
In the creation event we give the object a
vertical speed that is the same as the scrolling
speed of the background.
Motion, water, islands, ...
• To make sure that all other objects will stay
above the islands we give the island objects a
Depth of 10000.
• (You must run Game Maker in advanced
mode to be able to do this!) Instances of
objects are drawn in the order of the depth.
The instances with highest depth are drawn
first. Instances with lower depth are drawn on
top of them. So by giving the islands a high
depth they will always be drawn first and lie
below the other objects.
Now – a trick!
When the island disappears below the bottom
of the room we want to make it reappear at
the top. In the Step event of the island we
test whether the island disappeared below
the screen and, if so, let it reappear at the
top.
Note that the variable y indicates the vertical
position of the instance.
...... a trick!
A value of 0 corresponds to the top of the room.
The variable room_height indicates the height
of the room.
So the island disappears below the bottom of
the room when y is larger than room_height.
We can use the action to test variable values to
see whether the island lies below the room...
...... a trick!
So: When the island moves off of the screen at
the bottom, and can not be seen any longer, it
causes a copy of itself to be made above the
screen (where it can not be seen) and at a
random horizontal position.
It will then move down, onto the screen
(becoming visible) and off again, repeating...
Only one instance will be seen at a time.
This is actually computer programming!
...... a trick!
Motion
Motion
...... a trick!
You can use a variable name, and can actually
type full expressions here.
So the process is:
In Island object select a STEP event and choose
the ‘If a variable has a value’ action.
The room (what you can see) has a vertical size
(in pixels) of room_height, and starts at a
value of 0. This is the ‘y-axis’ as they told us
in high school.
The position of the island is the variable y.
So if y > room_height then we want to move
the island.
Where to move to?
Negative values of y are above the screen
(room).
Move islands to y = -65
Moving to the same x position is dull. Select a
random x within the room
random (room_width)
This is in a jump to a given position box in the
same STEP event.
The player’s airplane
Is controlled by keys.
The sprite we’ll use is a small GIF animation.
Makes it look like the propellers are moving.
Can shoot – space key.
Should look like the shooting comes from the
centre of the plane. Sprite is 65 pixels, centre is
32,32
Player
Motion events (initially) are the arrow keys.
Plane must not leave the room, so check!
<left>
if X is larger than 40
Jump to given position
-4, 0 relative to current.
Player
Similar for the other 3 directions:
<right>
<up>
<down>
if X is smaller than room_width-40
Jump to 4, 0 relative to current.
if Y is larger than 40
Jump to 0, -3 relative to current.
if Y is smaller than room_height-120
Jump to 0, 3 relative to current.
The player’s cannon
We need a bullet sprite. We put its origin in the
centre as we did for the main plane.
To make it a bit spectacular we use a rather large
bullet. Exaggerating things is often important in
games.
Create an object with this sprite.
Creation even: give it a vertical speed of –8 to
make it move upwards.
Destroy it once it leaves the room - in the step
event we test whether the variable x is smaller
than –16.
The player’s cannon
In the plane’s object box, make an event for
pressing the <space> key.
This event creates a new bullet instance.
An idea: only create one if there are no others. Use
the TEST INSTANCE COUNT as we did with
diamonds before.
The player’s cannon
We don't want too many bullets too fast. How
about two bullets every second?
This is one bullet every 15 steps.
Use a variable can_shoot
This is created in a create event for the plane by
using a set variable command box. We initially
set can shoot to 1 (true)
CAN SHOOT
Now in the event, keyboard, space key event:
– Is CAN SHOOT equal to 1?
If so, create a new bullet in front of the plane (0,16)
set CAN SHOOT to 0.
Set alarm0 to 15.
alarm0 ???
Alarms
An alarm is an ‘automatic’ event that happens
when a specified number of game steps have
taken place. It is like a timer.
If we set alarm0 to 15, then it becomes 0 in 15
steps. At that time and alarm0 event
happens, and we can use that to set the CAN
SHOOT variable back to 1 again.
Thus we can shoot every 15 steps.
Blocks
We also need to group actions in the <space>
event.
Enemy Planes
Type 1: It is a small plane that simply flies
downwards.
It does not shoot but when it hits the main plane
the game is lost.
1. Create sprite, read it in.
2. Create object, assign sprite, vertical speed=4
3. When plane hits the botton it redraws at
randome above the room.
Needs: collision with bullet, with player.
Enemy 1
Collision with bullet: it explodes and vanishes
Use ADD SOUND and load an explosion noise.
These are WAV files, prerecorded.
Need a sprite for the explosion, origin 16,16. It
is a small animation.
Once it finishes playing there is an event called
ANIMATION END that we use to destroy the
sprite (actually, we’ll MOVE it)
Bullet action,collision with plane1: delete self
Enemy 1
Collision with player: it explodes and vanishes
Use an explosion noise.
Game is over: print message and stop.
High Score
The Game should get harder...
We start with one enely plane, and spawn more and
more, and different kinds.
How do we do that? Using a game agent.
We create one more object: controller_enemy.
It will control the creation of enemy planes.
We make the object invisible during the game by
unchecking the box labeled Visible. A sprite is not
required for it.
The Game should get harder
In its creation event we create an enemy place at a
random location just above the room. (the first
enemy) We also set the alarm clock to 200.
In the event for this alarm clock we create another enemy
plane and set the alarm clock again, but this time to
500.
The effect is that at the beginning of the game there is
one enemy plane. After 200 steps, that is, about
seven seconds, a second
• enemy plane appears. After about 15 seconds, a third
plane appears, etc.
High Score