Writing Lua Code with LÖVE

LÖVE is a set of libraries for Lua, so it isn’t an application you launch to write code. Instead, you use LÖVE functions in your code.

If Geany isn’t still running, launch it now. Go to the File menu and select New. This creates an empty untitled file in your workspace. Select File ➤ Save As to save this file as main.lua in your dice project directory.

Creating variables for the size of the window doesn’t do anything special. These are normal variables containing normal numbers. It’s how the game script uses these variables that actually sets the window size.

The LÖVE game engine is programmed to do just two things automatically when it’s launched: call the love.load() function once, and then call the love.draw() function until the user quits. So for LÖVE to do anything with your game, you need to create both of those functions. LÖVE doesn’t care what’s in those functions; in fact, it expects you to fill that in yourself. In other words, it’s in these functions that the actual game code goes.

You’ve already used functions in Lua, but this time you are creating your own. A function in programming is a block of self-contained code that optionally accepts input and optionally renders data as output. You’ll also hear them called methods or even algorithms , but it’s all the same concept: you’re writing instructions for a computer, and by wrapping those instructions in a named function, you allow your program to use and reuse those instructions as often and whenever needed.

Spawning a window for your game is a one-time task. When the user launches your game, the window’s attributes—like the size, title, and background color—only need to happen once. After those attributes are set, LÖVE can move on to the rest of the code. This means, of course, that window setup should happen in the love.load() function .

It’s customary to indent code blocks to signify a kind of lineage. For instance, everything is indented after function love.load() to demonstrate that the lines of code are inside that function. The word end is not indented, and closes the function. In some programming languages, like Python, this is required, but in Lua, it’s entirely optional. Lua doesn’t use indentation to determine programming logic; it’s just a visual convention for programmers.

Most of the names of the functions are pretty descriptive, so you can probably surmise what they do. love.window.setMode sets the width and height of the window by using the variables view_w for width and view_h for height.

The love.window.setTitle function sets the title in the window’s title bar. love.graphics.setBackgroundColor sets the background of the window to the RGB value 0,0,0 (black).

It’s not much to look at, but you can launch your game as is. To see what you’ve created so far, first save your file. If you don’t remember to save before previewing your game, you won’t see your changes, so get used to saving often.

The cd command stands for change directory. The ~ symbol is shorthand for your home directory.

An empty window appears. Notice that its title is DiCE.

Close the window once your excitement has subsided. For this second iteration of the dice game, don’t worry about how the game looks, just focus on the code. Making the game look good happens in the next iteration.

Game Code

You know from the previous version of the dice game that there are three events that must happen for the game to work. The computer must roll die, the player must roll die, and then the values of the roll must be revealed.

In the previous version of the game, it was up to the user to compare the rolls and to determine who had won. This time, let Lua compare the values and determine the winner. To do that, you must use two of the most common logic tools in programming: math operators and an if/then statement.

An if/then conditional statement does exactly what an if/then statement does when you use one in everyday speech. If one thing is true, then do one thing; otherwise, do something else. In this example, the if/then statement hinges upon whether or not the contents of the player variable is greater than the contents of the computer variable. It would be equally effective if it depended upon computer being less than player.

From the LÖVE library, the code uses the graphics.setColor function to set the foreground color and the graphics.printf to print text on the screen. Just as the standard Lua print function requires a parameter—specifically what to print, the love.graphics.printf function requires several parameters: what to print, when to wrap text to the next line, the location along the X and Y axes, and text justification. These parameters must be given in the order specified by the function’s documentation, located at love2d.org/wiki/love.graphics.printf.

The game window opens, but it’s still just a blank window. This makes it seem like your game doesn’t work, but if you look at the terminal, assuming you launched the game in Geany, then you see that Lua did print a winner to your standard output. So the underlying game logic is sound.

The problem, in fact, is that your game’s text was written to the screen but only persisted for a millisecond or so. The love.load() function is only called once per launch, but a screen is refreshed constantly and at a rate much faster than your eye can detect. To generate graphics that are refreshed for as long as the game is running, use the love.draw() function .

This time, the winner is printed to the graphical game screen. The message also prints infinitely in your terminal, which provides you with some insight about why the text remains visible in the game window. The message isn’t just being written once, but several times as your screen refreshes.

Fonts

Fonts have the same requirements as graphics. To use them in your game, you have to send the font file along with your game, and to do that legally, you must respect the license of whatever font you choose. You might not think about it often, but the default fonts on Windows and Apple computers are mostly owned by Microsoft, Apple, Adobe, or other companies. You’re allowed to use them, but not necessarily to redistribute or sell them. Luckily, there are plenty of free and open source fonts available online.

Fonts don’t often use a Creative Commons license, but have their own special Open Font License or GNU General Public License, or similar. There are several good sites offering fonts. This example uses the boldly futuristic font Orbitron from TheLeagueOfMoveableType.com. It is a good source of openly licensed fonts but does not have so many options as to be overwhelming.

Create two new directories in your dice folder: one called font and the other called img. To create a new directory, right-click your dice folder and select New ➤ Folder.

Download the dice graphics as PNG files and also download the font. Place the dice graphic files in the img directory and the font TTF and LICENSE files in the font directory.

Winner and Loser

With all the important variables set depending on how the dice roll, the main loop has relatively little to do in terms of logic. However, the main loop is still important to keep the graphics going, so now it’s time to make sure that the interface responds appropriately to input.

You’ve already set the main loop to appear dormant until it receives input from the user, but it should also react once a mouse button is released. Specifically, it should look at the variables of the players to determine who has won the roll and announce the winner.

Insert another conditional statement in the main loop that checks for a winner. Announce the winner by printing a message to the screen using the love.graphics.printf function. To help differentiate between the human user and the computer, this example changes the foreground color to either green or red when writing the font to screen, and then back to white for general-purpose drawing.

You can choose whatever color you prefer. If you don’t think in RGB colors, use a color picker online. Traditionally, RGB values use 0 as empty and 255 as full, but LÖVE uses 0 as black and 1 as white, with all shades in between being a decimal value. You can convert from a 0–255 value to a decimal value by dividing by 255. For example, a color picker value of (188,54,0) is (188/255,54/255,0/255) or (0.73,0.21,0).

Try your game now. It responds to your click, changes the dice graphics, and announces a winner. What more could a user possibly want?

Well, since there’s no visual cue for the user that the game is waiting for a mouse click and hasn’t just crashed, it would be better user interface (UI) design to provide guidance for a new user. This can be implemented as an alternative to the start condition. If start is true, then that means the user has just started the game and has not yet clicked the mouse button (if the button had been clicked, the screen would display the winner and start would be set to false).