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Kivy: Interactive Applications in Python

Chapter 2. Graphics – The Canvas

Any Kivy Widget contains a Canvas object. Be careful with the name because it might be confusing:

Note

A Canvas is not the place where we draw. Instead, a Canvas contains all the drawing instructions that will render the graphical representation of the Widget.

The coordinate space refers to the place where we draw, what you might have thought to be the canvas is in the first place. In this chapter, you are going to learn how to draw and manipulate the representation of the widgets through the instructions that we add to the Canvas instances:

Draw basic geometric shapes (straight and curve lines, ellipses and polygons) through vertex instructions
Using colors and rotating, translating, and scaling the coordinate space through the context instructions
The difference between vertex and context instructions and how they complement each other
The three different sets of instructions of the Canvas that we can use to modify the order of execution
Storing and retrieving...

Key benefits

Use Kivy to implement apps and games in Python that run on multiple platforms

Discover how to build a User Interface (UI) through the Kivy Language

Glue the UI components with the logic of the applications through events and the powerful Kivy properties

Detect gestures, create animations, and schedule tasks

Control multi-touch events in order to improve the User Experience (UX)

Description

Mobiles and tablets have brought with them a dramatic change in the utility of applications. Compatibility has become essential, and this has increased the kind of interaction that users expect: gestures, multi-touches, animations, and magic pens. Kivy is an open source Python solution that covers these market needs with an easy-to-learn and rapid development approach. Kivy is growing fast and gaining attention as an alternative to the established developing platforms. Kivy: Interactive Applications in Python quickly introduces you to the Kivy development methodology. You will learn some examples of how to use many of the Kivy components, as well as understand how to integrate and combine them into big projects. This book serves as a reference guide and is organized in such a way that once finished, you will have already completed your first project. You will start by learning the Kivy Language for building User Interfaces (UI) and vector figures. We then proceed to the uses of Kivy events and properties to glue the UI with the application logic. You then go on to build an entire User Interface (UI) starting from a hand-made sketch. Furthermore, you will go on to understand how to use the canvas and drawing instructions to create different types of geometrical figures. Finally, you will be introduced to a big set of interactive and smooth features: transformations (scale, rotate, and translate), gestures, animations, scheduling tasks, and multi-touch elements. Kivy: Interactive Applications in Python expands your knowledge by introducing various components that improve the User Experience (UX). Towards the end of the book, you will be confident to utilize Kivy components and strategies to start any application or game you have in mind.

Who is this book for?

This book is aimed at Python developers who are familiar with Python and have a good understanding of concepts like inheritance, classes, and instances. No previous experience of Kivy is required, though some knowledge of event handling, scheduling, and user interfaces, in general, would boost your learning.

What you will learn

Build a User Interface (UI) using the Kivy Language

Understand and alter the order of execution of the drawing instructions

Use the powerful Kivy properties to keep the UI always updated with the last user interactions

Bind and unbind Kivy events to control widgets (UI components), touches, the mouse and keyboard, animations, and clock

Scale, rotate, and translate widgets

Control and switch between different screens

Develop and use your own single gestures

Create animations and combine them to bring widgets to life

Add different types of translations to the animations

Comprehend the main strategies to control the multi-touch events

Schedule single or repetitive tasks such as animations

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Instant access to your digital copy whilst your Print order is Shipped

Paperback book shipped to your preferred address

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Jason Crowe Dec 11, 2013

For anyone wanting to learn Kivy this book is a "must have". Even though this book isn't overly long, it takes you through everything you need to create your multi touch UI from start to finish.Before you choose a gui frontend you MUST read this book!

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Willina A. Clark Dec 15, 2013

DISCLAIMER: This book requires that you know python and are familiar with Kivy and the Kivy language.With that disclaimer out of the way, this book is essential to building games/interactive applications with Kivy. This book also provides you with tutorials to familiarize you with the language. The first is a comic drawing app and the other is a space invaders type game.Its an essential tool for understanding how the Kivy language works. It is not a book that teaches you python and that is something that needs to be reiterated. That does not take away from the vast amounts of information included in the book. Because Kivy is cross-platform, you could be running an app in no time.While this book isn't long (less than 150 pages), the Notes, the Kivy language coding examples and an in-depth index make it worth it's weight in gold. Definitely worth a read!!

Adam Rohacs Jan 05, 2014

The long and short of it - this book is not for beginners in Python, or beginners in programming. Or operating systems.Even the author says so on page 2: "The book aims at Python developers who want to create exciting and interesting UI/UX applications. They should be already familiarized with Python and have a good understanding of some software engineering concepts, particularly inheritance, classes, and instances [...]"What he fails to mention are OS differences and install issues. The book is short, and I think it's nice to skip the obligatory 3 or 4 primary chapters of filler that many books have where you "install" the OS/platform/etc., with the instructions being largely out-of-date. Having said that, it is no easy task to get Python and Windows playing together well, and so I'm guessing that the author assumes you have your OS figured out. I'm not sure that this is the best assumption to make. Providing a short page of URLs to install instructions and such would be a nice addition.Realistically, the best idea is if the reader is using Linux (and I'm sure some friends on the Python Facebook page will disagree...), preferably a Debian spin so that packages are easily installed and there is little to no breakage on update/upgrade of the OS. Better yet is if the reader understands how to install and use Virtualenv and is a Linux user. I had a few troubles getting Pygame installed in a .virtualenv for Arch, but it all worked out in the end. Check out the extended review for more info on that.To delve a bit more into what I mean by "don't use this book if you are beginner" - to make a long story short: 1. There are some convention/typo issues in the book, 2. many things are not explained that the reader is expected to know, 3. The book is overly technical, and sometimes I like a bit of layman speak to draw me in a bit. I can read docs, otherwise - books are good for reference but it is nice to be able to enjoy them as well.If you download all of the code and don't try to type any of it in, you might be able to get around some of the issues encountered, but while typing in the code - as it happens with many web tutorials on open source software - I ended up "fixing" a few things so that I could move forward.One issue that annoyed me is the author's usage (and non-usage) of tab conventions. Python uses a 4 space forced tab style, where the .kv language can use 2 spaces or more. It would have been nice for the author to stick to 4 spaces for both types of files - for consistancey and, most importantly - readability. This isn't Ruby, and so I see no reason to use two different styles of tabulation for the same application. That's as much of a knock on Kivy as anything, but the author could adjust and make the code more clear. E.g. There are points in the book where 2 spaces can look like no spaces, and then the .kv code breaks and you get a blank canvas instead of an application (or a page of debug logs in your virtualenv console).Back to "experience":Kivy is highly based on Widgets, so if you don't have a firm grasp on that concept in Python, it's gonna be a rough road. Even an experienced Python programmer might not be great in this area. I think it is better to learn that concept somewhere else and come back to the book again with better understanding of how widgets work.Moreover, it's not necessary to use the .kv language, but it can help. All coding can be done in Python classes if you like to program that way, and some do, so it might be nice to see the code done both ways.Layout: I don't like the way the beginning examples are layed out (before we get to the Comic project.) The code is broken up into pieces which can't be run independently. Combining the code together works, but once again - it's an experience thing. Does an experienced Python programmer know how to use Linux and the cat binary? Maybe, maybe not. It's possible to use an IDE and cut and paste pieces together - but why?And so instead, the reader might fall back on completed code instead of typing in code from the book, run it, and not learn as much by that process. In my humble opinion, there's no such thing as a "visual learner" when it comes to coding. You have to do it to learn it.Line numbers:Argh! The line numbers start, and never, ever end. Line numbers should start and end at each code snippet. The line numbers in this book extend *over chapters*. Not good at all, confusing, and a horrible oversight on the part of the editors. Packtpub - fix this, and please encourage your authors to not commit an atrocity like this again.The .kv files break Pep8 coding guidelines:This is why style and code should not mix. On page 27, this is blatantly obvious. Mixing ASCI codes with neo-html formatting inside quotes is not good if you add spaces according to Pep8. It would be nice to see pure Python code examples to go around this issue.In defense of the author and Packtpub ebook style: the book is not quite 150 pages long, so it's supposed to be a quick "HOWTO" to get a Kivy programmer started. I wonder if this format can actually work without references to dependancies and requisite knowledge needed for the task at hand.In closing, I'll say that this book is generally well written, and is a fantastic guide for an experienced Python programmer who wants to get into application development. The platform itself is very advanced and well designed and can export to various OS without license fees like other App engines have.For someone new to Python who isn't at least intermediate level with an OS like Ubuntu Linux, I'd say that you could still follow along and run the code examples, but that this book should be a goal for you to reach after learning Pep8, Widgets, classes, and other concepts that are necessary to be successful with this book. The author does explain this, but I'd guess that many will jump in head-first anyway and hope/expect the internet to be a good research/cheat tool. It won't be - nothing will substitute for knowledge and experience here.I applaud the author for making a very good first text to bring Kivy to the masses. Now, the real work begins on adding install guides online and links to style guides and best practices for the emerging Python programmer. As well, pure Python code examples could be added online as extra content.Enjoy!

stratos4 Dec 20, 2013

A very readable book which in just five chapters summarized the main features and benefits of using Kivy framework for cross platform development.From the first chapter, the reader is gradually led to write the applications which includes all the elements needed to programming applications for mobile devices.There are two projects in the book. The first one, the comic creator, exemplifies how to build a user interface, how to draw vector shapes in the screen, how to bind user interactions with pieces codes and other components related to improve theuser experience. The second project, Invaders Revenge, is an interactive game that introduces you to the use of scheduling of tasks, keyboard events, animations, and multi-touch control.

Ruby 'Vette Lover May 31, 2014

This book covers several applications and touches upon a wide range of topics. While it says that it is aimed at Python developers, a deep knowledge of Python is not really required. What it doesn't cover is readily available online. Although it was published last year, the code seems to work well with the latest version of Python and Kivy.

Kivy: Interactive Applications in Python: For Python developers this is the clearest guide to the interactive world of Kivi, ideal for meeting modern expectations of tablets and smartphones. From building a UI to controlling complex multi-touch events, it's all here.

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Kivy: Interactive Applications in Python

Chapter 2. Graphics – The Canvas

Note

Basic shapes

Note

Images, colors, and backgrounds

Rotating, translating, and scaling

Comic creator – PushMatrix and PopMatrix

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