Cross-platform game and app development for new programmers

Easy Does It

© Lead Image © Valeriy Kachaev, 123RF.com

© Lead Image © Valeriy Kachaev, 123RF.com

Article from Issue 252/2021
Author(s):

Ren'Py helps you create Android, Linux, macOS, Windows, and HTML5 games and apps.

Although you can find some excellent cross-platform development tools, many of these tools come with a steep learning curve for new programmers. Ren'Py [1] is a visual novel engine that has been around for more than 10 years, and it is one of the easiest packages to learn for game and app development.

The nice thing about Ren'Py is that you don't need any previous programming experience. Ren'Py uses a simple "screen language" that allows you to add backgrounds, images, character dialogs, and menus. For more complex requirements, Ren'Py supports inline Python and Python blocks.

The Ren'Py software development kit (SDK) is supported on Linux, macOS, and Windows, with final applications that can be built to run on Android, iOS, Linux, macOS, and Windows and in browsers with HTML5 (Figure 1).

Figure 1: Ren'Py development and build options.

In this article, I introduce Ren'Py with three examples. The first example will be the start of a visual novel. The second example will be a tourist guide with graphic menus, and the final example uses Python to create a dashboard screen that shows dynamic values and bars.

Getting Started

If you want to play with Ren'Py on a Raspberry Pi or an Ubuntu/Debian system, you can load a lightweight installation with:

sudo apt-get install renpy

The apt-get version of Ren'Py, however, does not have any tutorials or extra build features, so it is recommended that you go to the Ren'Py site for the complete installation directions [2].

The Ren'Py user interface creates new projects with all of the required files and supports all of the different build options (Figure 2). The script.rpy text file contains all the logic for an application.

Figure 2: Ren'Py interface.

Visual Novel

A visual novel is sort of like a comic book that can have multiple paths and story lines that users select as they work their way through the novel. The first step is to define some characters and background images. Creating character drawings from scratch can be a lot of work; luckily, you can find some open source solutions that can help out.

Character Creator [3] is an excellent free website you can use to generate male or female head, torso, and full-body images. It also supports a variety of facial expressions (Figure 3). The character image files and all background images are stored in the project's game/images directory.

Figure 3: Character Creator generates character emotions.

The next step is to use a standard text editor and add screen language code to the script.rpy file. Figure 4 and Listing 1 show the code required to display a background with a character and some dialog. Lines 3 and 4 define two characters cop and me. These definitions are used to output or show dialog text. Ren'Py uses labels to jump between code segments. The application begins at the start label (line 10).

Listing 1

Visual Novel

01 # darkstreet - script.rpy
02
03 define cop = Character("Cop")
04 define me = Character("Me")
05
06 image darkstreet = im.Scale("darkstreet.jpg",config.screen_width,config.screen_height)
07
08 # The game starts here.
09
10 label start:
11
12     # Show a background.
13     show darkstreet
14
15     show cop_head at truecenter
16
17     # These display lines of dialogue.
18
19     cop "Hey Kid! Stop right there!\n
20       Why do you have blood on your hands?"
21
22     hide cop_head
23     show me_crying_head at truecenter
24
25     me "It wasn't me...I don't know what happened."
26
27
28     return
Figure 4: Start of a visual novel.

Images in the game/images directory can be displayed simply with:

show image_name at position

In this example, cop_head.png is displayed at the center of the screen (line 15) by:

show cop_head at truecenter

Images can also be resized, rotated, moved, or adjusted. In line 6, the background (darkstreet.jpg) is sized to fill the screen. Dialog is shown by referencing the character and then the dialog text (lines 19-20).

Figure 5 shows the next phase of the story. The policeman is hidden with the hide statement (line 22) and an image of a crying girl (me_crying_head) is shown with some dialog (line 25). The use of hide and show statements allow you to present different characters and backgrounds.

Figure 5: Second character in the visual novel.

At the end of the story, the application finishes with a return statement (line 28).

Tourist Guide

Most apps and games require menus that allow multiple branches or outcomes. A Ren'Py menu is created simply with a menu: statement. Each menu item is defined with button text and a jump statement, which is like an old-school Basic GOTO statement. Each jump has a label to which the code links.

Figure 6 shows the start of a tourist guide for the Bruce Peninsula [4]. A menu is called at the start of the program. Each menu item jumps to a specific section of the code with a label. Within a subsection, (e.g., the beach), a new background and text are shown. After the user sees this information, a jump start statement puts the user back to the main menu.

Figure 6: Tourist guide with menus.

For smaller applications (Figure 7), you can put the submenus, display logic, and Python code directly in the menu: logic.

Figure 7: Submenus and logic within menu options.

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