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- Herausgeber: Packt Publishing
- Kategorie: Fachliteratur
- Sprache: Englisch
This book is intended for programmers who are comfortable with the Python language and who want to build desktop and mobile applications with rich GUI in Python with minimal hassle. Knowledge of Kivy is not strictly required—every aspect of the framework is described when it's first used.
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Seitenzahl: 337
Veröffentlichungsjahr: 2015
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Table of Contents
Kivy Blueprints
Kivy Blueprints
Copyright © 2015 Packt Publishing
All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.
Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.
Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.
First published: January 2015
Production reference: 1230115
Published by Packt Publishing Ltd.
Livery Place
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Birmingham B3 2PB, UK.
ISBN 978-1-78398-784-9
www.packtpub.com
Credits
Author
Mark Vasilkov
Reviewers
Takumi Adachi
Joe Dorocak
Raphael Pierzina
Edward C. Delaporte V
Commissioning Editor
Usha Iyer
Acquisition Editor
Vinay Argekar
Content Development Editor
Kirti Patil
Technical Editors
Arwa Manasawala
Rahul Shah
Copy Editors
Roshni Banerjee
Gladson Monteiro
Karuna Narayanan
Project Coordinator
Nidhi Joshi
Proofreaders
Martin Diver
Maria Gould
Paul Hindle
Joanna McMahon
Indexers
Hemangini Bari
Rekha Nair
Priya Subramani
Graphics
Sheetal Aute
Production Coordinator
Nilesh R. Mohite
Cover Work
Nilesh R. Mohite
About the Author
Mark Vasilkov is a software craftsman—or engineer—whichever you prefer. He specializes in Python and JavaScript development, mostly related to web and mobile applications, and has 10 years of experience in hacking stuff together so that it mostly works.
For what it's worth, Mark is a Russian Israeli. This very book was partially written in a bomb shelter due to Hamas shooting long-range rockets (containing warheads with up to 200 kg explosives each) at Tel Aviv. Israel is a beautiful country, inspiring everyone in the region to do something truly remarkable and idiosyncratic.
About the Reviewers
Takumi Adachi is currently working as an Android developer for Applocation based in Victoria, British Columbia, Canada. He enjoys programming, kendo, cycling, and video games. He is a proponent for open source and strictly uses the MIT license for his personal projects and code. He specializes in Java, Python, JavaScript, and web markup languages such as HTML and CSS. He is exposed to a wide range of technologies such as JavaScript, Python, HTML, CSS, SQL, SQLite, Vagrant, AngularJS, PHP, node.js, Git, REST, JSON, Bash, Linux, OS X, Windows, nginx, VirtualBox, Visual Studio 2013, Java, Excel, Android, and so on.
He has helped review the book, Kivy Blueprints, and hopes to continue reviewing books for Packt Publishing.
I would like to thank my cousin, Justin, parents, teachers, and employers for providing me with opportunities to grow and develop, and supporting me in my endeavors.
Joe Dorocak, whose Internet moniker is Joe Codeswell, is a very experienced programmer. He enjoys creating readable code that implements the project requirements efficiently and understandably. He considers writing code akin to writing poetry.
He prides himself on the ability to communicate clearly and professionally. He considers his code to be communication, not only with the machine platforms upon which it will run, but with all those human programmers who will read it in the future.
He has been employed either as a direct employee or as a contractor by IBM, HP, GTE/Sprint, and other top-shelf companies. He is presently concentrating on app and web project consulting, coded primarily, but not exclusively, in Python and JavaScript. For more details, please check Joe's LinkedIn profile at https://www.linkedin.com/in/joedorocak.
Raphael Pierzina is currently working as a development lead at Mackevision (http://mackevision.com/) in Germany. He is responsible for a Python/PySide-based standalone application for defining and managing complex configuration logic data sets for data-based visualization in terms of code reviews and supervision. He holds a bachelor's degree in virtual design and specializes in computer graphics and interactive applications.
Raphael is passionate about idiomatic Python code and development techniques such as TDD. He enjoys contributing to open source projects such as Cookiecutter (https://github.com/audreyr/cookiecutter) and occasionally posts on his personal blog (http://www.hackebrot.de/) about various topics, including MaxScript, comic books, and his adventures in the world of Linux.
I would like to thank my loving family and my close friends for their support over the course of this project. Thank you for your understanding when I had little time to spare. I wish to express my gratitude to the team at Packt Publishing for providing me with the opportunity to be a part of this amazing book.
Edward C. Delaporte V leads a software development group at the University of Illinois and has contributed to the documentation of the Kivy framework. He is thankful to all those whose contributions to the open source community made his career possible, and he hopes this book helps to attract enthusiasts to software development.
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To my wife, Natalia
Preface
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:
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.
Note
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 (http://kivy.org/); 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:
A terminal session
Running a Kivy application (basically, a Python program) is achieved similarly:
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:
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?
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.
Reader feedback
Feedback from our readers is always welcome. Let us know what you think about this book—what you liked or disliked. Reader feedback is important for us as it helps us develop titles that you will really get the most out of.
To send us general feedback, simply e-mail <[email protected]>, and mention the book's title in the subject of your message.
If there is a topic that you have expertise in and you are interested in either writing or contributing to a book, see our author guide at www.packtpub.com/authors.
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You can download the example code files from your account at http://www.packtpub.com for all the Packt Publishing books you have purchased. If you purchased this book elsewhere, you can visit http://www.packtpub.com/support and register to have the files e-mailed directly to you. Another option of getting the up-to-date source code is by cloning the GitHub repository, https://github.com/mvasilkov/kb.
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Errata
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Questions
If you have a problem with any aspect of this book, you can contact us at <[email protected]>, and we will do our best to address the problem.
Making the clock tick
UI frameworks are mostly event-driven, and Kivy is no exception. The distinction from the "usual" procedural code is simple—the event-driven code needs to return to the main loop often; otherwise, it will be unable to process events from a user (such as pointer movement, clicks, or window resize), and the interface will "freeze". If you're a longtime Microsoft Windows user, you are probably familiar with programs that are unresponsive and freeze very often. It is crucial to never let this happen in our apps.
Practically, this means that we can't just code an infinite loop like this in our program:
Technically, it might work, but the application's UI will stay in the "not responding" state until the application gets killed (forcefully stopped) by the user or an operating system. Instead of taking this faulty approach, we need to keep in mind that there is a main loop running inside Kivy, and we need to take advantage of it by utilizing events and timers.
Event-driven architecture also means that in many places, we will listen to events to respond to various conditions, be it user input, network events, or timeouts.
One of the common events that many programs listen to is App.on_start. A method with this name, if defined on the application class, will be called as soon as the app is fully initialized. Another good example of an event that we will find in many programs is on_press, which fires when the user clicks, taps, or otherwise interacts with a button.
