Week 10 - Game Simulations

Date: 2026-10-26

today:

• Data Structure Gardens
• Little performances
• Coding challenge: Squirrel Eat Squirrel

Data Structure Garden

This is a review of building up arrays of objects, complete with their own lifespan.

In this tutorial, we will use L5 to simulate an interactive flower garden. In this project, your digital canvas will contain 20 randomly generated flowers, each a different color and size. Clicking on the canvas adds new, unique flowers. Each flower is programmed with a wilting animation. This animation causes the flowers to slowly shrink and vanish, much like the natural cycle of a flower’s life.

Step 1: Make a single flower object

Let’s start our flower garden by creating one flower. We can start by drawing it using an ASCII character, so we need data on the x-coordinate, the y-coordinate, and the character for our flower. We’ll use a ‘@’ symbol to represent our first flower

• Create a flower object by bundling the flower’s canvas coordinates with the character used to draw it. Let’s store the object in a variable named flower. Add this code above setup():

-- Flower Object
local flower = {
  x = 200,
  y = 100,
  char = '@' 
}

function setup()
  size(400, 400)
end

• Print your object to the console by adding the following line of code in setup(). Note that we loop through our table of key-value pairs using pairs(tablename):

for i,val in pairs(flower) do
  print(i,val)
end

which returns the output:

x   200
y   100
char    @

• Set the background to ‘lightblue’

Your code should look like this:

require("L5")

-- Flower Object
local flower = {
  x = 200,
  y = 100,
  char = '@' 
}

function setup()
  size(400, 400)
  
  -- Print object in console.
  for i,val in pairs(flower) do
    print(i,val)
  end
end

function draw()
  background('lightblue')
end

Try running your code. You should see your flower object printed out to the console.

Here’s the general syntax for defining an object:

-- Define an object
local objectName = {
  property1 = value1,
  property2 = value2,
  property3 = value3
}

The syntax for objects uses:

• curly braces ({}) to enclose a bundle of properties;
• Properties can be names, such as the names of variables or functions, or they can be strings, or even other tables. When using spaces in property names, Lua requires square brackets to interpret them correctly. For example, I might create an object with a property for a ‘first name’ and a ‘last name,’ like this:

local ironMan = {
  ['first name'] = 'Tony',
  ['last name'] = 'Stark'
}

• If your property has no spaces, the quotes and brackets around the property name are optional, such as first_name = 'Tony'.
• an equal sign (=) to separate each property with specific values;
  • Values can be of any datatype, and can even be a function!
• commas (,) to separate each [property] = value pair

You can store objects by initializing new variables when you define them. In the code above, you declared a variable named flower. You then initialized the flower variable with an object whose properties represent a flower that can be drawn on the window.

To check the properties and values of an object, you printed the key value pairs from the table.

Step 2: Use your object

You can access any value stored in object properties by using its square bracket name as shown above or its variable name, property name, and dot notation like so (as long as the property name doesn’t have spaces in it or special characters, in which case you will need to use the square brackets syntax):

-- Access the object's property1 value with dot notation.
objectName.property1

• Use the text() function with flower object properties to place the flower on the canvas.
• We can specify a color for the text and place that before writing to the screen
  • In draw(), add the following code:

-- Fill shapes and text with a specified carnation pink color
fill('pink')
  
-- Display flower object.
text(flower.char, flower.x, flower.y)

• You can use textSize() before the text function to set the size of the flower.

-- Increase the text size
text(100)

Your code should look like this:

require("L5")

-- Flower Object
local flower = {
  x = 200,
  y = 100,
  char = '@' 
}

function setup()
  size(400, 400)
end

function draw()
  background('lightblue')

  -- Increase the text size
  textSize(100)

  -- Fill shapes and text with a specified carnation pink color
  fill('pink')
  
  -- Display flower object
  text(flower.char, flower.x, flower.y)
end

To access values in the flower object, we use dot notation, which uses the dot operator to access properties and values within objects.

In the code above, you accessed:

• the character for the flower with flower.char
• the x-coordinate with flower.x
• the y-coordinate with flower.y

Since these values represent strings and numbers, they can be used in the text() function, similar to the way variable names are used to access the value they store.

Try this:

• Add a size property to the flower object.
• Replace the textSize() value with the flower object’s size.

Step 3: Define a createFlower() function

Now, let’s define a function that can display different flowers on the canvas. We will define a createFlower() function that will allow us to customize the flower objects we create. We want to make sure that we can change the x- and y-coordinates for different flowers. We also want to change their size and color. One way to do that is to add new properties to the flower object for size and color. In this project, we also want the flower to appear, then disappear after some time. To do this, we will also include a lifespan property for our flower object.

We want our createFlower() to return information when it’s called, just like the built-in text() function returns text on the canvas. Therefore, we must specify a return value. Using return values is a great way to save information computed by the function in a variable or array.

In this example, we will be using random() to create variety in our flowers when they’re drawn on the canvas.

• Define the createFlower() function, which creates a random flower object. All values will be set randomly each time createFlower() is called.
  • Outside of draw() and setup(), add the following function declaration:

-- Function that creates a random flower object.
function createFlower() 
  -- Define a flower object.
  local flower = {
    x = random(20, 380),
    y = random(20, 380),
    size = random(20, 75),
    lifespan = random(255, 300),
    color = color(random(255), random(255), random(255)),
  }
  -- Return the flower object.
  return flower
end

• Test the createFlower() function by using it to create a flower object, and store it in a variable called myFlower.
  • Add the following in the draw() function:

-- Create flower object
local myFlower = createFlower()

Draw an ellipse on the canvas using myFlower properties. * Add the following in the draw() function:

-- Use flower object properties to draw an ellipse.
fill(myFlower.color)
ellipse(myFlower.x, myFlower.y, myFlower.size)

• Slow down the rate at which each flower appears by changing the frame rate to one frame per second. In setup(), add: frameRate(1).

Your code should look like this:

require("L5")

function setup() 
  size(400, 400)
  frameRate(1)
end

function draw() 
  background("lightblue")

  -- Create flower object.
  local myFlower = createFlower()

  -- Use flower object properties to draw an ellipse.
  fill(myFlower.color)
  ellipse(myFlower.x, myFlower.y, myFlower.size)
end

function createFlower() 
  -- Define flower object.
  local flower = {
    x = random(20,380),
    y = random(20,380),
    size = random(20,75),
    lifespan = random(255,300),
    color = color(random(255), random(255), random(255)),
  }
  
  -- Return flower object.
  return flower
end

In the code above, you use createFlower() to create and return a new flower object with random values, then store the object in the variable myFlower. myFlower is used to access its property’s random values, which are used to draw an ellipse on the canvas. Each time draw() runs, a new random flower object is created, and its properties are used to draw a new random ellipse on the canvas.

Visit the L5 reference to learn more about random().

Try this:

• Change the random range for the flower’s x and y location and size.
• Get creative with the color generation; maybe it’s shades of only blues, reds, or purples.

Step 4: Define the drawFlower() function with a parameter

Now that we know that createFlower() creates and returns a new flower object, let’s define the drawFlower() function. Our drawFlower() function will receive a flower object as an argument and place it on the canvas. This will help make our code organized and manageable.

• Outside of all other functions, define the drawFlower() function with one parameter representing a flower object.

function drawFlower(flower)
end

• Inside the drawFlower() function, draw the attributes of a flower, including the petals and center of the flower. Remember to use the flower object properties for the x and y locations, size, and color. You can add the following code to the function body:

noStroke()
fill(flower.color)

-- Draw petals.
ellipse(flower.x, flower.y, flower.size / 2, flower.size);
ellipse(flower.x, flower.y, flower.size, flower.size / 2)

-- Draw a yellow center.
fill(255, 204, 0)
circle(flower.x, flower.y, flower.size / 2)

Next, we will test the drawFlower() function. Add the following to the draw() function.

-- Testing drawFlower().
let flower1 = createFlower();
drawFlower(flower1)

Your code should look similar to this:

require("L5")

function setup()
  size(400, 400)
  frameRate(1)
end

function draw()
  background("lightblue")

  -- Testing drawFlower().
  local flower1 = createFlower()
  drawFlower(flower1)
end

function createFlower()
  local flower = {
    x = random(20,380),
    y = random(20,380),
    size = random(20,75),
    lifespan = random(255,300),
    color = color(random(255), random(255), random(255))
  }
  return flower
end

function drawFlower(flower) 
  noStroke()
  fill(flower.color)

  -- Draw petals.
  ellipse(flower.x, flower.y, flower.size / 2, flower.size)
  ellipse(flower.x, flower.y, flower.size, flower.size / 2)

  -- Draw a yellow center.
  fill(255, 204, 0)
  circle(flower.x, flower.y, flower.size / 2)
end

In the code above, createFlower() is used to create and return a random flower that is stored in flower1. The random flower (flower1) is then passed into drawFlower(), which accesses the flower object properties to draw a flower on the canvas. This process occurs each time the draw() function runs, so random flowers appear and disappear on the canvas.

Step 5: review - Arrays of objects

Before we move on to making our garden of flowers by using an array, let’s better understand how arrays work with a few simple examples. Arrays are objects that can store multiple values in one variable name. Each value is stored in an element with a specific location known as its index. The index of the first element in any array in Lua is 1.

Tables are used for arrays and objects in Lua.

Example of building an array with a Lua table:

-- This is an ordered table, AKA a list or array
local fruits = {'apple', 'banana', 'cherry', 'dragon fruit', 'elderberry', 'fig', 'grape', 'honeydew'}

Each item in this array can be accessed with a number, beginning at the index 1.

print(fruits[1]) -- 'apple'
print(fruits[3]) -- 'cherry'

Prepending a # to a table gives us the length (total elements) in an array. So we can get the very last item from the list very easily, no matter how many items are in that array.

print(fruits[#fruits]) -- 'honeydew'

Example 1: Creating and drawing an array of names

require("L5")

-- Create an array flowers
local flowers = {"Rose", "Daisy", "Tulip"}

function setup()
  size(200, 200)

  background(220)

  -- Draw the first name.
  fill('red')
  text(flowers[1], 10, 50)
  
  -- Draw the second name.
  fill('green')
  text(flowers[2], 10, 100)
  
  -- Draw the third name.
  fill('blue')
  text(flowers[3], 10, 150)
end

local flowers = {"Rose", "Daisy", "Tulip"}

In this example, we’ve created an array using curly brackets ({ }) and commas that separate each element in the array. The array is a collection of strings, each representing a type of flower, and is stored in a variable called flowers. Each element of the array holds a string with a flower name. Each element can be accessed using its index number. For example, "Rose" is located at index 1, "Daisy" at index 2, and "Tulip" at index 3.

local rose = flowers[1]

In the code snippet above, we access the first element of the flowers array at index 1 using the index notation: flowers[1]. In the example above, this syntax is used to place text on the canvas with the names accessed from various elements in the flowers array.

We then assign that value to a new variable named rose. rose now holds the string "Rose", which is the first flower name in the flowers array. Values stored in other elements can be accessed in the same way.

Example 2: Using a for loop to iterate through the array of names

require("L5")

-- Create an array flowers
local flowers = {"Rose", "Daisy", "Tulip"}

function setup()
  size(200, 200)
end

function draw()
  background(220)
  fill(0)
  
  -- Use a for loop to iterate over the array.
  for i=1,#flowers do
    text(flowers[i], 10, 50 * i)
  end
end

Our second example uses a for loop to iterate through each element in the array and print the text on the canvas. Iteration is a process where a block of code is executed repeatedly for each element in an array.

for i=1,#flowers do
  text(flowers[i], 10, 50 * i)
end

To iterate, the code snippet above uses a for loop that “looks through” each element of the flower array. According to the for loop, the index i starts at 1 and increases with each iteration until it reaches the max number of elements in the array. Arrays in Lua start their index at 1. The last element in the array can be accessed by referencing the item stored at the length of the array. The number of elements in any array can be accessed by using the array# symbol. In the for loop above, the length of the flowers array is accessed using #flowers. To access the values in the array, we use flowers[i] in the for loop in the text() function to display the value in each element as text on the canvas.

Example 3: Adding new elements to the array

require("L5")

-- Create an array flowers
local flowers = {"Rose", "Daisy", "Tulip"}

function setup()
  size(200, 200)
  table.insert(flowers, "Sunflower"); --add new element

  background(220)
  fill(0)
  
  -- Use a for loop to iterate over the array.
  for i=1,#flowers do
    text(flowers[i], 10, 40 * i)
  end
end

local flowers = {
"Rose", "Daisy", "Tulip" --Inserted elements will go here
}

-- Add a new element to the end of the array
table.insert(flowers, "Sunflower")

Using the array method table.insert(), you can add a new element to the end of the array. In this example, we are adding “Sunflower” to the end of the flowers array.

Example 4: Removing an array element

require("L5")

-- Create an array flowers
local flowers = {"Rose", "Daisy", "Tulip"}

function setup()
  size(200, 200)
  fill(0)
  
  -- Starting at index 1, remove one flower.
  table.remove(flowers, 1)

  background(220)
  
  for i=1,#flowers do
    text(flowers[i], 10, 50 * i)
  end
end

local flowers = {"Rose", "Daisy", "Tulip"}

-- remove one element from flowers at index 1
table.remove(flowers, 1)

In order to remove elements from an array, we use the function table.remove(). The function table.remove(flowers, 1) modifies the flowers array with two parameters: one for the array, and another for the index of where to start removing. You can optionally add a third that specifies the number of elements to remove. table.remove(flowers, 1) results in the removal of "Rose" from the array, leaving only "Daisy" and "Tulip".

Example 5: Using for..in loop for arrays

require("L5")

-- Create an array flowers
local flowers = {"Rose", "Daisy", "Tulip"}

function setup()
  size(200, 200)
  
  background(220)
  fill(0)
  local y = 50
  
  -- Use the for loop with ipairs to look at each element as a variable.
  for i, flower in ipairs(flowers) do
    text(flower, 10, i * y)
  end
end

for i, flower of ipairs(flowers) do
-- flower declares a variable to store each current element
-- ipairs is the keyword to loop through each ordered element in an array
-- flowers is the name of the array to loop over

  --do something with the current element
  print(flower)
end

We can also iterate over an array using a for..in loop. The flower variable temporarily stores each element during the loop’s iteration. The print(flower) statement inside the loop prints the name of each flower to the console, cycling through "Rose", "Daisy", and "Tulip" in order.

Using a for...in loop can make code easier to read when things become more complex.

Step 6: Generate multiple flowers with an array

Now, it’s time to generate multiple flowers on the screen using arrays.

• First, declare the flowers array at the top of your program. The curly brackets with nothing in them represent an empty array of flowers.

-- Array of flowers.
local flowers = {}

• Outside of all other functions, define the flowerPower() function.

-- Function to create 20 flowers.
function flowerPower()
end

Inside flowerPower(), create 20 flower objects using a for loop and add them to your flowers array.

for i=1,20 do
  -- Create a flower in a random location.
  local flower = createFlower()
  -- Add the flower to the flowers array.
  table.insert(flowers, flower1)
end

Call the flowerPower() function in the setup() function to create the 20 flower objects.

flowerPower()

• Use the for..in loop with ipairs for arrays in the draw() function to draw each flower in the flowers array. The for..in loop reads, for each flower element in the array of flowers, call drawFlower().

for i,flower in ipairs(flowers) do
  drawFlower(flower)
end

Your code should look similar to this:

require("L5")

-- Array of flowers.
local flowers = {}

function setup()
  size(400, 400)
  frameRate(1)

  -- Generate 20 flowers.
  flowerPower()
end
function draw()
  background("lightblue")

  -- For each flower in the array of flowers.
  for _,flower in ipairs(flowers) do
    drawFlower(flower)
  end
end

-- Function to create 20 flowers.
function flowerPower()
  for i=1,20 do
    -- Create a flower in a random location.
    local flower = createFlower()

    -- Add the flower to the flowers array.
    table.insert(flowers, flower)
  end
end

-- ... createFlower() and drawFlower()
function createFlower()
  local flower = {
    x = random(20,380),
    y = random(20,380),
    size = random(20,75),
    lifespan = random(255,300),
    color = color(random(255), random(255), random(255))
  }
  return flower
end

function drawFlower(flower) 
  noStroke()
  fill(flower.color)

  -- Draw petals.
  ellipse(flower.x, flower.y, flower.size / 2, flower.size)
  ellipse(flower.x, flower.y, flower.size, flower.size / 2)

  -- Draw a yellow center.
  fill(255, 204, 0)
  circle(flower.x, flower.y, flower.size / 2)
end

Try this:

Add a parameter to your flowerPower() function so you can easily start with as many flowers as you like.

Step 7: Update the flowers in the array

Now that we have tested the array of flowers, let’s draw the wilting effect. One of the benefits of using an array to control the flowers is the ability to update values in each flower.

• Outside of all other functions, define a function called updateAndDrawFlowers():

function updateAndDrawFlowers()
end

This function will look at each flower in the array and will draw the flower.

for i,flower in ipairs(flowers) do
  drawFlower(flower)
end

• Inside the for loop, decrease the flower object’s size and lifespan to simulate wilting.

Add a wilting animation effect, which will decrease the flower size by 1% after the drawFlower() function draws the flower. We create the wilting effect by multiplying the current size by 0.99 and storing it back into the flower’s size property. Then decrement the lifespan and store it in the flower’s lifespan variable.

-- Wilting effect for the flower
flower.size = flower.size * 0.99

-- Reduce lifespan.
flower.lifespan = flower.lifespan - 1

• When the flower object’s lifespan is zero or negative, we’ll remove it from the array by using the table.remove() method.

for i,flower in ipairs(flowers) do
  -- Draw the flower.
  drawFlower(flower)

  -- Wilting effect for the flower.
  flower.size = flower.size * 0.99

  -- Reduce lifespan
  flower.lifespan = flower.lifespan - 1
  
  if flower.lifespan <= 0 then 
    -- Remove wilted flower.
    table.remove(flowers, i)
  end
end

• Add updateAndDrawFlowers() to the draw() function.

• Remove the call to frameRate(1) from setup().

Your code should look similar to this:

require("L5")

-- Array of flowers.
local flowers = {}; 

function setup()
  size(400, 400)
  
  -- Generate 20 flowers.
  flowerPower(); 
end

function draw()
  background('lightblue')
  
  -- Call your new function.
  updateAndDrawFlowers()
end

-- Define your new function
function updateAndDrawFlowers()
  for i,flower in ipairs(flowers) do

    -- Draw the flower.
    drawFlower(flower)

    -- Apply wilting effect by reducing size by 1%
    flower.size = flower.size * 0.99

    -- Reduce lifespan
    flower.lifespan = flower.lifespan - 1
    
    if flower.lifespan <= 0 then 
      -- Remove wilted flower.
      table.remove(flowers, i)
    end
  end
end

-- Function to create 20 flowers.
function flowerPower()
  for i=1,20 do
    -- Create a flower in a random location.
    local flower1 = createFlower()
    
    -- Add the flower to the flowers array.
    table.insert(flowers,flower1)
  end
end

function createFlower()
  local flower = {
    x = random(20,380),
    y = random(20,380),
    size = random(20, 75),
    lifespan = random(255,300),
    color = color(random(255), random(255), random(255))
  } 
  
  return flower
end

function drawFlower(flower)
  noStroke()
  fill(flower.color)
  
  -- Draw petals.
  ellipse(flower.x, flower.y, flower.size / 2, flower.size)
  ellipse(flower.x, flower.y, flower.size, flower.size / 2)

  -- Draw center.
  fill(255, 204, 0)
  circle(flower.x, flower.y, flower.size / 2)
  
end

Try this:

Experiment with the wilting effect using subtraction, random numbers, or any other ideas you come up with.

Step 8: Add more flowers to the array with mousePressed()

Finally, let’s add more flowers to the canvas by using mousePressed(), mouseX(), and mouseY to add another flower object to the flowers array each time the window is clicked.

• Outside of all other functions, write your mousePressed() function:

function mousePressed()
  local flower = createFlower()
  
  -- reassign x to be mouseX
  flower.x = mouseX
  
  -- reassign y to be mouseY
  flower.y = mouseY
  
  -- add the flower to the flowers array
  table.insert(flowers, flower)
end

Your code should look something like this:

require("L5")

-- Array of flowers.
local flowers = {}; 

function setup()
  size(400, 400)
  
  -- Generate 20 flowers.
  flowerPower(); 
end

function draw()
  background('lightblue')
  
  -- Call your new function.
  updateAndDrawFlowers()
end

function mousePressed()
  local flower = createFlower()

  -- reassign x to be mouseX
  flower.x = mouseX; 
  
  -- reassign y to be mouseY
  flower.y = mouseY

  -- add the flower to the flowers array
  table.insert(flowers,flower)
end

function updateAndDrawFlowers()
  for i,flower in ipairs(flowers) do

    -- Draw the flower.
    drawFlower(flower)

    -- Apply wilting effect by reducing size by 1%
    flower.size = flower.size * 0.99

    -- Reduce lifespan
    flower.lifespan = flower.lifespan - 1
    
    if flower.lifespan <= 0 then 
      -- Remove wilted flower.
      table.remove(flowers, i)
    end
  end
end

-- Function to create 20 flowers.
function flowerPower()
  for i = 1, 20 do
    -- Create a flower in a random location.
    local flower1 = createFlower()
    
    -- Add the flower to the flowers array.
    table.insert(flowers,flower1)
  end
end

function createFlower()
  local flower = {
    x = random(20,380),
    y = random(20,380),
    size = random(20, 75),
    lifespan = random(255,300),
    color = color(random(255), random(255), random(255))
  } 
  return flower
end

function drawFlower(flower)
  noStroke()
  fill(flower.color)
  
  -- Draw petals.
  ellipse(flower.x, flower.y, flower.size / 2, flower.size)
  ellipse(flower.x, flower.y, flower.size, flower.size / 2)

  -- Draw center.
  fill(255, 204, 0)
  circle(flower.x, flower.y, flower.size / 2)
  
end

By Portia Morrell, Jaleesa Trapp, Kate Maschmeyer. Adapted to L5 by Lee Tusman. CC BY-NC-SA 4.0

Coding Challenge: Squirrel Eat Squirrel

Squirrel Eat Squirrel is a game by programmer Al Sweigart.

Squirrel Eat Squirrel is loosely based on the game Katamari Damacy. The player controls a small squirrel that must hop around the screen eating smaller squirrels and avoiding larger squirrels. Each time the player’s squirrel eats a squirrel that is smaller than it, it grows larger. If the player’s squirrel gets hit by a larger squirrel larger than it, it loses a life point. The player wins when the squirrel becomes a monstrously large squirrel called the Omega Squirrel. The player loses if their squirrel gets hit three times.

Images: some squirrels from Open Game Art

Homework

Squirrel Eat Squirrel

Basic Requirements:

• game works in fullscreen mode
• a player’s squirrel. controlled by up, down, left, right arrow
• Procedurally generated ‘squirrels’
• when an enemy squirrel collides with another squirrel the big one eats the smaller one and grows bigger
• if the player hits a larger squirrel, lose a life point and grow smaller
• if player hits a larger squirrel three times, game over

Advanced:

• procedurally generate grass around the level. Grass is like a squirrel that doesn’t move!
• balance the variables so the game gets to a compelling level of difficulty (the ‘goldilocks’ amount)
• better ‘walking’ pattern. hop? perlin noise?
• eating sounds
• procedurally generated flowers
• what else?

DOUBLE BONUS POINTS:

• self-playing version (‘player’ moves itself without player), possibly through Perlin noise

Reading and Write

Read Writing Aliens OR Duchamp, Markov, Queneau: A Mostly Delightful Quilt - 1 hour

Finish Squirrel Eat Squirrel