Projects
Catch the dots
Make a dot-catching game
Step 1 Introduction
In this project you’ll learn how to create a game in which the player has to match up coloured dots with the correct colour of the controller wheel.
What you will learn
How to choose random items from a list
How to use variables to track speed, lives, and the player’s score
What you will need
Hardware
A computer capable of running Scratch 3
Software
Scratch 3 (either online (https://rpf.io/scratchon) or offline (https://rpf.io/scratchoff))
Downloads
Offline Scratch 2 project (https://rpf.io/p/en/catch-the-dots-go)
Additional notes for educators
You can find the completed project here (https://rpf.io/p/en/catch-the-dots-get).
Step 2 Create a controller
Start by creating a controller that the player will use to collect dots.
Open the ‘Catch the dots’ Scratch starter project.
Online: open the starter project at rpf.io/dots-on (https://rpf.io/dots-on).
If you have a Scratch account you can make a copy by clicking Remix.
Offline: download the starter project from rpf.io/p/en/catch-the-dots-go (https://rpf.io/p/en/catch-the-dots-go), and then open it in the Scratch offline
editor.
If you need to download and install the Scratch offline editor, you can find it at rpf.io/scratchoff (https://rpf.io/scratchoff).
You should see a controller sprite:
Add some code to the controller sprite to make the sprite turn right if the player presses the right arrow key:
when clicked
forever
if key right arrow pressed? then
turn 3 degrees
Test your code. The controller should spin to the right when you press the right arrow key.
Add code to the controller sprite to make the sprite turn left if the player presses the left arrow key.
I need a hint
Here is what your code should look like:
when clicked
forever
if key right arrow pressed? then
turn 3 degrees
if key left arrow pressed? then
turn 3 degrees
Step 3 Gain points or lose lives
Now you’re going to add some dots that the player needs to collect.
Create a new sprite called ‘red’. This sprite should be a small red dot.
Add this script to your ‘red’ sprite to create a new clone of the sprite every few seconds:
when clicked
hide
wait 2 seconds
forever
create clone of myself
wait pick random 5 to 10 seconds
If you click the green flag now, it looks like nothing is happening. This is because all of the cloned sprites are hidden, and they appear in the same place.
You are going to add code to make each new clone appear in one of the four corners of the Stage.
Create a new list called start positions, click the list’s (+) icon to add the values -180 and 180.
Make a list
Click on Make a List under Variables.
Type in the name of your list. You can choose whether you would like your list to be available to all sprites, or to only a specific sprite. Click OK.
Once you have created the list, it will be displayed on the stage, or you can untick the list in the Scripts tab to hide it.
Click the + at the bottom of the list to add items, and click the cross next to an item to delete it.
New blocks will appear and allow you to use your new list in your project.
Then you can hide the list by unselecting this box:
Notice that the coordinate for each corner of the Stage is a combination of 180 and -180. This means you can use the list to pick a corner of the Stage at random.
Add this code to the ‘dot’ sprite to make each new sprite clone appear in a random corner and then slowly move towards the controller sprite.
when I start as a clone
go to x: item pick random 1 to 2 of start positions y: item pick random 1 to 2 of start positions
point towards controller
show
repeat until touching controller ?
move 1 steps
This new code chooses either -180 or 180 for the x and y positions, meaning that each ‘dot’ sprite clone starts in a corner of the Stage.
Test your project. You should see red dots appear in the corners of the Stage and move slowly towards the controller.
Create two new variables called lives and score.
Add code to your Stage to set the lives variable to 3 and the score to 0 at the start of the game.
when clicked
set lives to 3
set score to 0
Add this code to the end of the Stage’s script to make the game end when the player loses the last of the lives:
wait until lives < 1
stop all
The player should win points for catching dots, and should lose lives for failing to catch dots. A dot can only be caught by matching the colour of the controller to the colour of
the dot.
Go back to the ‘red’ dot sprite’s Scripts area to add some code blocks to the end of the sprite’s when I start as a clone script.
First, make the dot clone move 5 steps so that it overlaps the controller.
Then add code to either add 1 to score if the colour of the dot clone matches the colour of the controller when they touch, or to take 1 away from lives if their
colours don’t match.
Adding a sound from the library
Select the sprite you want to add the sound to.
Click the Sounds tab, and click Choose a Sound:
Sounds are organised by category, and you can hover over the icon to hear a sound. Choose a suitable sound.
You should then see that your sprite has your chosen sound.
move 5 steps
if touching color ? then
change score by 1
play sound pop until done
else
change lives by -1
play sound Laser1 until done
delete this clone
Test your game to make sure that:
1. You lose a life if you don’t match a dot with the correct colour
2. You score a point if you match a dot correctly
Step 4 More dots
Duplicate your ‘red’ dot sprite twice, and name the two new sprites ‘yellow’ and ‘blue’.
Change the costume of each new sprite so it is the correct colour: the ‘yellow’ sprite should be yellow, and the ‘blue’ sprite should be blue.
Change the code of each sprite so that the player has to match dot clone to the correct colour on the controller to score points.
I need a hint
This is how you need to change the code for the yellow sprite:
if touching color ? then
change score by 1
start sound pop
This is how you need to change the code for the blue sprite:
if touching color ? then
change score by 1
start sound pop
If you play the game now, you can see that the dots sometimes get created on top of each other.
Change the code for the ‘yellow’ dot sprite so that it waits four seconds after the flag is clicked before appearing.
when clicked
hide
wait 4 seconds
Then change the code for the ‘blue’ dot sprite so that it waits 6 seconds after the flag is clicked before appearing.
Step 5 Increase the difficulty
Now you’re going to make the game more difficult the longer the player plays it. You will do this by making the dots appear faster and faster over time.
Create a new variable called ‘delay’.
Go to the Stage’s Scripts area and create a new script that sets the delay variable to 8 and then slowly reduces the value of delay while the game runs.
when clicked
set delay to 8
repeat until delay = 2
wait 10 seconds
change delay by -0.5
Notice that this code is very similar to the code you would use to create a countdown timer!
Next, use the delay variable in the code scripts of the ‘red’, ‘yellow’, and ‘blue’ sprites.
Remove the code block that makes the game wait a random number of seconds between making the dot sprite clones. Replace the block you’ve removed with your
new delay variable:
wait pick random 5 to 10 seconds
wait delay seconds
Do this for all three dot sprites.
Test the game, and check whether the dots begin to appear more quickly as the game goes on.
Does this work for all three coloured dots?
Can you see that the value of the delay variable decreases?
Step 6 Challenge: faster dots
Can you improve your game by adding a speed variable and using this new variable to make the dot change their speed over time? The clones should start by moving one
step at a time, and then steadily get faster and faster.
The code you need for this is very similar to the code in which you’ve used the delay variable.
Step 7 High score
You’re going to save the game’s high score, so that players can see how well they are doing.
Create a new variable called high score.
Select the Stage. Click on ‘My blocks’ and create a new custom block called check high score.
Add code to your custom block so that the block checks if the current value of score in larger than the value of the high score variable, and then stores the value
of score as the new value of high score.
define check high score
if score > high score then
set high score to score
Add your new custom block to the Stage script before the end of the script.
when clicked
set lives to 3
set score to 0
wait until lives < 1
check high score
stop all
Play your game twice to check whether your score gets correctly saved as the high score.
Step 8 Challenge: improve your game
Can you think of ways to improve your game? For example, you could create special dots that:
Double your score
Slow down the dots
Hide all the other dots on the screen
Can you add a menu with buttons to your game? You could add a screen with instructions or a separate screen for showing the high score.
Step 9 What next?
Try the Clone wars (https://projects.raspberrypi.org/en/projects/clone-wars?utm_source=pathway&utm_medium=whatnext&utm_campaign=projects) project to
make a game in which you have to save the Earth from space monsters. In that project, you will be able to use what you have learned about cloning sprites and adding a
score!
Score as many points as you can by shooting flying space-hippos. If you get hit by a hippo or by an orange dropped by the bats, you lose a life.
Published by Raspberry Pi Foundation (https://www.raspberrypi.org) under a Creative Commons license (https://creativecommons.org/licenses/by-sa/4.
0/).
View project & license on GitHub (https://github.com/RaspberryPiLearning/catch-the-dots)
