Programming Fundamentals  
Lecture 02Introduction to Löve 2D  
Edirlei Soares de Lima  
<edirlei.lima@universidadeeuropeia.pt>  
Computer Graphics Concepts  
What is a pixel?  
In digital imaging, a pixel is a single square  
or rectangle point in a raster image (or the  
smallest addressable element in a display  
device).  
Pixels are placed in a grid-like fashion and  
together they draw images on screen.  
The location of a pixel is usually referred  
by its position x on the horizontal axis and  
y on the vertical axis of the grid (pixel  
coordinates).  
Computer Graphics Concepts  
What is a color?  
In computer graphics, colors are generally defined by the intensity  
chromaticity) of three additive primaries color (or channels): red,  
green, and blue.  
(
RGB Scale:  
R
G
B
255  
More Intensity  
0
Less Intensity  
Don’t know the RGB value of the  
color that you want?  
Important: the RBG scale used  
by Löve is between 0 and 1.  
Computer Graphics Concepts  
Computer graphics uses coordinate systems to represent  
positions on a virtual scene.  
There are usually:  
2 axis to define a 2D space (x and y);  
3 axis to define a 3D space (x, y, and z);  
Warning: different tools/frameworks  
use different coordinate systems  
1 unit = 1 pixel / arbitrary scene units;  
Origin at the top left / origin at the  
center / origin at the bottom left;  
y goes up / y goes down;  
Löve 2D Coordinate System  
200  
800  
0
x
100  
(200,100)  
600  
y
“Hello World” in Löve  
function love.draw()  
love.graphics.print("Hello World", 360, 300)  
end  
The function love.graphics.print  
is used to draw a text on screen. The last  
two parameters represent the position (x  
and y) where the text will be drawn.  
Programming in Löve  
Programming in Löve involves the implementation of callback  
functions. A callback is a function that you code and Löve  
automatically calls at certain times.  
Example:  
love.draw()  
The callback love.drawis called continuously to draw all  
the graphical elements (images, geometric shapes, text,  
etc.) on the screen every frame.  
Löve Callbacks  
Löve has several callbacks to perform various tasks (all of them  
are optional):  
Initialization, rendering, update, user input keyboard/mouse/joystick, ...  
A fully-featured game experience would probably utilize nearly  
all of Löve callbacks, so it's wise to know what they are.  
List of Löve callbacks: https://www.love2d.org/wiki/Category:Callbacks  
More common callbacks:  
love.load()  
love.draw()  
love.update(dt)  
Callback love.load()  
The callback love.load()is called exactly once at the  
beginning of the game.  
Is usually used to:  
Load resources (images, audio, etc.)  
Initialize variables  
Set specific settings  
function love.load()  
image = love.graphics.newImage("cake.jpg")  
love.graphics.setColor(0, 0, 0)  
love.graphics.setNewFont(12)  
love.graphics.setBackgroundColor(255, 255, 255)  
end  
Back to the “Hello World”  
function love.load()  
love.graphics.setColor(0, 0, 0)  
love.graphics.setBackgroundColor(1, 1, 1)  
end  
function love.draw()  
love.graphics.print("Hello World", 360, 300)  
end  
The function love.graphics.setColor  
defines the color used to drawn things on  
screen (RGB model)  
The function love.graphics.  
setBackgroundColor defines the  
background color (RGB model)  
Callback love.update(dt)  
The callback love.update(dt)is called continuously while  
the game is running (every frame). The parameter 'dt' stands for  
"
time this function was called (usually a small value like 0.02571).  
delta time" and it represents amount of seconds since the last  
Is usually used to:  
Implementation of the game logic  
Physics simulations  
Artificial intelligence computations  
Calculates the value of px at a  
constant rate (independently of the  
speed of the computer)  
function love.update(dt)  
px = px + (100 * dt)  
end  
Back to the “Hello World”  
local px  
-- position of the text in the x axis  
function love.load()  
love.graphics.setColor(0, 0, 0)  
love.graphics.setBackgroundColor(1, 1, 1)  
px = 0  
end  
function love.update(dt)  
px = px + (100 * dt)  
end  
function love.draw()  
love.graphics.print("Hello World", px, 300)  
end  
Löve Modules  
Löve comprises several modules:  
Every module has a set of functions and data types that can be used  
for game programming.  
All modules are contained in a global module called love.  
Example of module: love.graphics  
In the previous examples we used some functions from the  
love.graphicsmodule.  
The function love.graphics.printis part of the  
love.graphicsmodule.  
List of Löve modules: https://love2d.org/wiki/love  
Module love.graphics  
The love.graphicsmodule contain functions dedicated for  
graphical operations:  
Draw lines, geometric shapes, text, images, etc.  
Load external files (images, fonts, etc.) into memory.  
Create special objects (particle system, canvas, etc.)  
Manipulate the screen  
A complete list of functions of the love.graphicsmodule is  
available at: https://love2d.org/wiki/love.graphics  
Module love.graphics  
Drawing basic geometric shapes:  
Rectangle:  
love.graphics.rectangle(mode, x, y, width, height)  
Example:  
love.graphics.rectangle("fill", 300, 250, 200, 100)  
mode: “fill” to draw the shape filled  
or “line” to draw just an outline.  
Module love.graphics  
Drawing basic geometric shapes:  
Circle:  
love.graphics.circle(mode, x, y, radius, segments)  
Example:  
love.graphics.circle("fill", 400, 300, 50, 100)  
Number of segments used for  
drawing the circle  
Module love.graphics  
Drawing basic geometric shapes:  
Line:  
love.graphics.line(x1, y1, x2, y2, ...)  
love.graphics.line(300, 300, 500, 300)  
Example:  
More points are accepted as  
parameters.  
Module love.graphics  
Drawing basic geometric shapes:  
Polygon:  
love.graphics.polygon(mode, ...)  
Example:  
love.graphics.polygon("fill", 350, 300, 450, 300, 400, 200)  
More points are accepted as  
parameters.  
Module love.graphics  
Drawing basic geometric shapes:  
Changing the color of the geometric shapes:  
love.graphics.setColor(red, green, blue, alpha)  
Example:  
love.graphics.setColor(0, 1, 0)  
love.graphics.rectangle("fill", 300, 250, 200, 100)  
The alpha is optional and can be used  
to define colors with transparency.  
Geometric Shapes - Example  
function love.draw()  
-- draw a rectangle  
love.graphics.setColor(0, 0.521, 0)  
love.graphics.rectangle("fill", 100, 100, 600, 400)  
-- draw a polygon  
love.graphics.setColor(0.988, 0.988, 0)  
love.graphics.polygon("fill", 120, 300, 400, 120,  
680, 300, 400, 480)  
-
- draw a circle  
love.graphics.setColor(0, 0, 0.552)  
love.graphics.circle("fill", 400, 300, 120, 100)  
end  
Geometric Shapes - Example  
Exercise 1  
1
) Using basic geometric shapes (lines, rectangles, circles, and  
polygons), implement a program to draw a scene similar to the  
one illustrated below:  
Hints:  
Start simple and add one  
element at a time.  
Test after adding each  
element.  
Extra challenge:  
Draw a character in the  
scene using basic shapes:  
Exercise 2  
2
) Rewrite the code of the last exercise using functions. Create  
one function for each of the elements of the scene and try to  
make them parameterized.  
Example:  
function DrawTree(x, y, height)  
love.graphics.setColor(0.5, 0.2, 0)  
love.graphics.rectangle("fill", x - 20, y - height, 40, height)  
love.graphics.setColor(0.2, 0.6, 0)  
love.graphics.circle("fill", x, y - height, 80)  
end  
function love.draw()  
DrawTree(200, 500, 200)  
DrawTree(400, 500, 300)  
DrawTree(600, 500, 250)  
end