Book Image

Kivy Blueprints

Book Image

Kivy Blueprints

Overview of this book

Table of Contents (17 chapters)
Kivy Blueprints
About the Author
About the Reviewers
The Python Ecosystem


Mobile applications ceased to be the "new hotness" a long time ago, and these days users routinely expect that new software—be it a videogame or a social network—has a mobile version. Similar trend affects desktop operating systems; writing cross-platform software, once uncommon, has swiftly become a norm. Even game developers, usually limited to Microsoft operating systems on desktop, can be seen working on Mac and Linux ports for many new titles (for example, Steam, at the time of writing, hosts more than a hundred games that run on Mac and more than 50 that run on Linux).

This is especially valuable for start-ups and indie developers: building truly cross-platform software widens the potential audience, which leads to increased sales and may create good press along the way.

On the downside, writing portable software can be a very resource-hungry process, and this also affects small developers much more than big corporations.

In particular, many platforms have a preferred programming language and software development kit (SDK): iOS apps are mostly written in Objective-C and Swift, Android suggests the subpar Java programming language, and Microsoft promotes the use of the .NET framework, especially C#, for building Windows software.

Employing these tools allows you to leverage the native user interface and underlying functionality of an OS, but it also automatically prevents code reuse. This means that even if you are equally proficient in all programming languages and interfaces involved, porting the code may still take a non-trivial amount of time and introduce new bugs.

Write once, run anywhere

This whole situation creates a demand for a universal, multi-platform way to program. The problem isn't exactly new: one solution to it, created by Sun in 1995, is the Java programming language. Its marketing promise—write once, run anywhere—was never fulfilled and the language itself is unreasonably cumbersome to use. This led to many mocking variations of the slogan, culminating with write once, run away that refers to many developers abandoning Java in favor of better programming languages, including Python.

Not coincidentally, Kivy—the main topic of this book—is a graphical user interface library facilitating easy creation of multi-platform Python applications. The main features of Kivy toolkit are as follows:

  • Compatibility: Kivy-based apps work in Linux, Mac OS X, Windows, Android, and iOS—all from a single codebase.

  • Natural user interface: Kivy bridges the gap between different input methods, allowing you to handle a multitude of possible user interactions with similar code, mouse events and multitouch gestures alike.

  • Fast hardware-accelerated graphics: OpenGL rendering makes Kivy suitable for creating graphics-heavy applications such as videogames, and also improves the user experience with smooth transitions.

  • The use of Python: Kivy apps are written in Python, one of the better general purpose programming languages. In addition to being inherently portable, expressive, and readable, Python features a useful standard library and a rich ecosystem of third-party packages, the Python Package Index (PyPI).

Speaking of third-party packages, Kivy can be seen as a superset of many battle-tested components: a large part of its functionality relies on well-known libraries such as Pygame, SDL, and GStreamer. The API that Kivy exposes, however, is very high-level and unified.

It's worth mentioning that Kivy is free and open source MIT licensed software. In practice, this means that you can use it commercially without paying licensing fees. Its full source code is hosted on GitHub, so you can also patch bugs or add new features to it.

What this book covers

Chapter 1, Building a Clock App provides a gentle introduction to writing applications with Kivy. It covers the Kivy language, layouts, widgets and timers. By the end of the chapter we build a simple Clock app, similar to the one found in your cellphone.

Chapter 2, Building a Paint App is a further exploration of the Kivy framework's components and functionality. The resulting Paint app showcases the customization of built-in widgets, drawing arbitrary shapes on canvas and handling multi-touch events.

Chapter 3, Sound Recorder for Android serves as an example of writing a Kivy-based Android app. It shows how to use the Pyjnius interoperability layer to load Java classes into Python, which enables us to mix Android API calls with a Kivy-based user interface.

Chapter 4, Kivy Networking is a hands-on guide to building a network application from the ground up. In covers a number of topics, from creating a simple protocol to writing server and client software in Python, and culminates with the Kivy Chat application.

Chapter 5, Making a Remote Desktop App exemplifies another way of writing client-server apps. This chapter's program is based on the HTTP protocol—the one that powers the Internet. We develop a command-line HTTP server first, and then build the Remote Desktop client app with Kivy.

Chapter 6, Making the 2048 Game walks you through building a playable replica of the 2048 game. We demonstrate more complex Kivy functionality, such as creating custom widgets, using Kivy properties for data binding, and processing touch screen gestures.

Chapter 7, Writing a Flappy Bird Clone introduces another Kivy-based game, this time it's an arcade game similar to the well-known Flappy Bird title. Over the course of this chapter we discuss the use of texture coordinates and sounds effects, implement arcade physics and collision detection.

Chapter 8, Introducing Shaders demonstrates the use of GLSL shaders in the context of a Kivy application. In this tutorial you will learn about OpenGL primitives such as indices and vertices, and then write incredibly fast low-level code that runs directly on the GPU.

Chapter 9, Making a Shoot-Em-Up Game continues where the previous chapter left off: we use the knowledge of GLSL in order to build a side-scrolling shooter. A reusable particle system class is developed along the way. This project concludes the series and capitalizes on many techniques that were explained throughout the book, such as collision detection, touch screen controls, sound effects and so on.

Appendix, The Python Ecosystem, gives you more on Python libraries and tools.

Setting up the working environment

This section briefly discusses the requirements needed to effectively follow the narrative, implement, and run Kivy applications. Personal computer running a modern operating system—a Mac, Linux, or Windows box—is implied.

A note on Python

Python is the primary programming language used in the book; good knowledge of it, while not strictly necessary, may help.

At the time of writing, there are two incompatible versions of Python in wide use. Python 2.7 is monumentally stable but no longer actively developed, and Python 3 is a newer and slightly more controversial version bringing many improvements to the language, but occasionally breaking compatibility along the way.

The code in this book should largely work in both Python versions, but it may need minor adjustments to be fully compatible with Python 3; for best results, it's recommended that you use Python 2.7, or the latest Python 2 version available for your system.


Installing Python separately for Kivy development is not necessary on most platforms: it either comes preinstalled (Mac OS X), bundled with Kivy (MS Windows), or included as a dependency (Linux, Ubuntu in particular).

Installing and running Kivy

Kivy can be downloaded from the official site (; just choose an appropriate version and follow the instructions. This whole procedure should be pretty straightforward and simple.

Kivy downloads

To check whether the installation is working, follow these instructions:

  • On a Mac:

    1. Open

    2. Run kivy.

    3. The Python prompt, >>>, should appear. Type import kivy.

    4. The command should complete with no errors, printing a message along the lines of [INFO] Kivy v1.8.0.

  • On a Linux machine:

    1. Open a terminal.

    2. Run python.

    3. The Python prompt, >>>, should appear. Type import kivy.

    4. The command should print a message similar to [INFO] Kivy v1.8.0.

  • On a Windows box:

    1. Double-click kivy.bat inside the Kivy package directory.

    2. Type python at the command prompt.

    3. Type import kivy.

    4. The command should print a message similar to [INFO] Kivy v1.8.0.

    A terminal session

Running a Kivy application (basically, a Python program) is achieved similarly:

  • On a Mac, use kivy

  • On Linux, use python

  • On Windows, use kivy.bat (or drag-and-drop the file on top of kivy.bat).

Note on coding

Programming typically amounts to working with text a lot; hence, it's important to choose a good text editor. This is why I profoundly recommend trying Vim before you consider other options.

Vim is one of the better text editors largely available; it's highly configurable and built specifically for effective text editing (way more so than a typical alternative). Vim has a vibrant community, is actively maintained, and comes preinstalled with many Unix-like operating systems—including Mac OS X and Linux. It is known that (at least some) developers of the Kivy framework also prefer Vim.

Here are some quick Kivy-related tips for Vim users out there:

  • Python-mode ( is great for writing Python code. It throws in a lot of extra functionality, such as stylistic and static checker, smart completion, and support for refactoring.

  • Source code of GLSL shaders can be properly highlighted using the vim-glsl syntax (

  • Kivy texture maps (the .atlas files, covered in Chapter 8, Introducing Shaders) are basically JSON, so you can use, for example, vim-json (, and add a file association to your .vimrc file like this:

    au BufNewFile,BufRead *.atlas set filetype=json
  • Kivy layout files, .kv, are slightly more complicated to handle as they're similar to Python, but don't really parse as Python. There is an incomplete Vim plugin in the Kivy repository, but at the time of writing, Vim's built-in YAML support highlights these files better (this obviously might change in future). To load .kv files as YAML, add the following line to your .vimrc file:

    au BufNewFile,BufRead *.kv set filetype=yaml

Clearly, you are not obliged to use Vim to follow examples of this book—this is but a mere suggestion. Now let's write a bit of code, shall we?

Hello, Kivy

When learning a new programming language or technology, the first thing demonstrated to students is traditionally a "hello, world" program. This is how it looks in Python:

print('hello, world')

The Kivy version of a "hello, world" is a little lengthier and consists of two files, namely, a Python module and a .kv layout definition.


A Kivy application's entry point is customarily called, and its contents are as follows:

from import App

class HelloApp(App):

if __name__ == '__main__':

As you can see, this takes Kivy's App class, adds absolutely nothing to it, and calls run().


A layout file is typically named after the application class, in this case HelloApp, sans the App suffix and in lowercase: hello.kv. It contains the following lines:

    text: 'Hello, Kivy'

This is a very simple Kivy layout definition consisting of a single widget, Label, with the desired text inside. Layout files allow building complex widget hierarchies in a concise, declarative fashion, which is clearly not displayed here, but will be heavily used over the course of this book.

If we run the program now (refer to the Installing and running Kivy section for details), this is what we'll get:

Our first application powered by Kivy

Now you're ready to move on to the first chapter and start writing real programs.

Who this book is for

This book is intended for programmers who are comfortable with the Python language and who want to build desktop and mobile applications with a rich graphical user interface in Python with minimal hassle. Knowledge of Kivy, while certainly won't hurt, is not required—every aspect of the framework is described when it's first used.

At various points in this book, we will make an analogy between Kivy and web development practices. However, an extensive knowledge of the latter also isn't required to follow the narrative.


In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.

Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: "Kivy application's entry point is customarily called"

A block of code is set as follows:

from import App

class HelloApp(App):

if __name__ == '__main__':

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

# In Python code

Any command-line input or output is written as follows:

pip install -U twisted

New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: "The first event handler is for the Start and Stop buttons."


Warnings or important notes appear in a box like this.


Tips and tricks appear like this.

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