Sunday, April 07, 2013

Simple computer program for one year olds

Kids love to use the same things that their parents are using. Rather than buying them toy versions of objects, we use these opportunities to teach them the correct way to use everyday objects.

My son loves to see us use the computer, and wants to use a computer too. So we bought a real adult keyboard at an electronic store, and attached it to a real computer running Linux. The only thing he can do is hit a key and see the computer's reaction.  In most programs, this produces no visible result.

So I wrote a very simple program in Python using Gtk to display a single character from the keyboard in a huge font. This is what the computer looks like when it is running this program:


Lots of advantages to this approach:
  1. The child uses a "real" keyboard and a real computer, something that parents use too.
  2. There is no way to exit, except to Alt-Tab to switch programs.
  3. The child can be rough with the spare keyboard, you just buy a new one.
  4. The computer can be disconnected from the Internet, and put on a spare child account if required.
  5. The program should work on Windows and Mac as well, after you set up Python + Gtk.
The entire program is listed here:
#!/usr/bin/python

import gtk, string, pango

class BigChar():
    """ Create a Gtk window for a single giant textview that accepts all keyboard input. """
    def on_key_press(self, widget, data=None):
        """ Intercept all keypress events and show ascii
            characters. This requires the CAPS_LOCK to be off.  We
            don't intercept CAPS NUM or SCROLL lock, probably
            should."""
        ascii_value = data.keyval
        if (ascii_value >= 97 and ascii_value <= 122):
            self.textBuffer.set_text(string.ascii_uppercase[ascii_value-97])
            start = self.textBuffer.get_start_iter()
            end = self.textBuffer.get_end_iter()
            self.textBuffer.apply_tag_by_name("real_big", start, end)

    def __init__(self):
        """ Create a window with a single giant text view. Disables all chrome.
        """
        self.w = gtk.Window(gtk.WINDOW_TOPLEVEL)
        # No border
        self.w.set_border_width(0)
        self.w.realize()
        # Take over the entire screen
        self.w.fullscreen()

        # Connect the callback on_key_press to the signal key_press.
        self.w.connect("key_press_event", self.on_key_press)
        # Make the widget aware of the signal to catch.
        self.w.set_events(gtk.gdk.KEY_PRESS_MASK)

        # Add a text view to show the key pressed
        self.textView = gtk.TextView()
        # Disable a cursor in the text view.
        self.textView.set_editable(False)
        self.textView.set_can_focus(False)
        # Show the single character in the middle
        self.textView.set_justification(gtk.JUSTIFY_CENTER)
        # This is the place we will write the character to
        self.textBuffer = self.textView.get_buffer()
        # Make the text view huge, blue on white
        fontdesc = pango.FontDescription("monospace 512")
        self.textView.modify_font(fontdesc)
        tag = self.textBuffer.create_tag("real_big", background="white", foreground="red")

        # Make the text view take the entire window
        self.hbox = gtk.HBox(homogeneous=False, spacing=0)
        self.hbox.pack_start(self.textView, expand=True, fill=True)
        self.w.add(self.hbox)

    def show(self):
        """ Show the window"""
        self.w.show_all()


if __name__ == '__main__':
    # Create a bigchar window, and show it.
    bigchar = BigChar()
    bigchar.show()
    gtk.main()



Tuesday, March 19, 2013

Sound Sleep: Free application for Android

Frustrated by existing sleep-time applications, I wrote a simple application to play music on an Android phone. The application is called Sound Sleep and it is available for free on the Play Store.

To use the application, create a subdirectory called "sleeping" under the "music" directory in the SD-card or external storage. Put night-time sleep music in this subdirectory. Many music file formats (mp3, ogg, ...) are supported. All directory names are case insensitive.

Start the application. The top half of the screen starts and stops night-time music.

The bottom half starts/stops white noise.


Since the application allows tapping anywhere, it is perfect for clumsy night-time use. It works on all Android devices starting with version 1.5, so give it a try!

Monday, February 25, 2013

Adding photography grid lines in GIMP

In photography, the "Rule of thirds" suggests places for optimal visual interest. You divide the photo into nine equal parts, like a tic-tac-toe board. The rule says that the most important visual elements must be at the dividing lines, or along the lines of the tic-tac-toe. This is an easy rule, and helps to determine how best to crop an image, or to judge a composition.

GIMP, the free image editor, allows the user to create guide lines. These are lines shown for reference while editing an image. They do not modify the underlying image, and can be dragged out from the ruler or created using a menu item. Gimp also allows certain edits to stick to guide lines. This is useful if you are adding text, or adding layers as it makes it easy to align visual elements in an appealing manner.

I find it helpful to create rule of thirds guide lines to evaluate photographs. Rather than manually drag out guide lines, I have written a GIMP script to automatically create such rule-of-thirds guide lines. This is what the result looks like.


To use, download the rule-of-thirds script and copy it to your local scripts directory. On my machine, this is $HOME/.gimp-2.6/scripts. The exact location depends on your platform (Windows/Linux/Mac) and Gimp version. You can find out the exact location by going to [Menu] -> Edit -> Preferences -> Folders -> Scripts.

Now start gimp and navigate to [Menu] -> Filters -> Script-Fu -> Refresh scripts.

Once it is refreshed, the rule of thirds guide lines should be available under [Menu] -> Images -> Guides -> Photography.


Tuesday, February 12, 2013

Customers want control over their mobile device

Disclaimer: I'm a Google employee.

"The average consumer doesn't care about whether their mobile device is locked down"

I've heard this argument very often. However, the data just doesn't support it. Over the last week, the hacker group evasi0n released a program to jailbreak an iOS device. iOS devices (iPhones and iPads) are closed down: Apple chooses which programs can be installed by device owners. A jailbreak removes this restriction, and allows the device owner to install any program of their choice on their device.

The initial justification for such unprecedented control was that the phone network could not handle poorly written applications. This argument was bogus even when the iPhone came out. At that time, arbitrary applications could be executed on existing phones. Palm Treo and Blackberry both allowed the device owner to choose which applications to run. Not all applications were passed through careful scrutiny: the device owner could write his own application and run it on the device. With the advent of Android, this argument is even more hollow. Google sells Android devices on which the user can not just install any application, but also install any system software.

Other justifications claim that users want a third-party to control their experience and are willing to submit control of their own devices. The data suggests otherwise. The hack by evasi0n was downloaded by four million unique devices in just five days. We don't have any concrete numbers for iOS 6.x devices, but let's try to use people's estimates to arrive at how significant the five million figure is.

Apple announced the number of iOS devices in October 2011: 250 Million.
Rough numbers for devices runing iOS version 6.x: 100 Million.

So 5% of the total user base chose to jailbreak their device within the first four days. There are lots of caveats: the figures are all guess-work (the fact that the numbers are nice round figures should also make you suspicious). We don't know the exact number of 6.x devices, and Jay Freeman, the creator of Cydia, admits that many jailbreakers weren't counted because the jailbreak servers crumbled under the heavy load.

Even so, 5% of the users want control over their own device. And that's within a week of the jailbreak being available. A very conservative estimate is that another 5 million users jailbreak their device. So 10% of the users choose to control their own device. (This is again a rough guess, since total iOS version 6.x devices is a moving target.)

Keep in mind that the entire idea of a jailbreak is somewhat scary. I suspect most users would hesitate to download a program from an unknown website and run it on a costly phone or tablet. Put another way, the number of users who want to jailbreak their device is larger than the ones that do perform the jailbreak.

When one in ten of your users wants something, it isn't a fringe phenomenon anymore. They are sending you a strong message: that they want control over their own device.

Monday, February 11, 2013

Android framework debugging through IntelliJ

I had blogged earlier about using the Android Open Source Project (AOSP) to learn about the Android framework, and help debug your Android applications.

I missed out how easy it is to do this through IntelliJ, the other popular IDE.

IntelliJ is an IDE that was released in 2001, and has boasted an impressive feature set. It started out as a paid product and a community edition was released in 2009, along with source code licensed under the Apache License 2.0. A commercial version is still sold, and that includes enterprise support. For an Android developer's perspective, the community edition is a great product to use for all Android development. This post shows how to get set up and start debugging your project with full cross-references into the AOSP framework code.  This is a great way to learn the intricacies of the framework.

Installing IntelliJ IDEA


  1. Download IntelliJ IDEA community edition for your platform. Linux, Mac and Windows versions are available. At the time of writing this post, version 12 was the latest.
  2. Install it according to the instructions for your platform.

Set up JDK

Android development needs a Java Development Kit installed on the device. I choose to use Sun's Java 1.6, but you are free to use any JDK of your choice.
Configure -> Settings -> Project
It will say "No SDK". Click on New and select the path to your jdk. This is probably in /usr/local/sun-java-1.6, or somewhere else.


Set Android SDK

You should also have the Android SDK downloaded. If you need to download the SDK, notice that you need just the SDK for other IDEs, not the entire ADT. Say you unzip it into /usr/local/android-sdk-linux:
export ANDROID_SDK=/usr/local/android-sdk/linux

Create a new project on the previous screen.


On the following screen, create an "Android Application Module" and set the location of the Android SDK:

The project name doesn't much matter. You could create a Hello World project for the purpose of this guide. After clicking no "New", you need to set it to the path of the Android sdk, which is the location where you expanded the Android SDK zip file: ${ANDROID_SDK}.  You can change this setting later under  Menu bar -> File -> Other Settings -> Default Project Settings -> Platform Settings SDKs -> Project Structure.
This can also be set on a per-project basis. However, you should never need to change the SDK location. Instead, you can change the Build Target to the version of Android you wish to support. A single SDK location can hold multiple build targets (Starting from the earliest version of Android all the way to the latest.
At the end of this, you should have a Hello World Android project. IntelliJ supports looking up code sources if you have downloaded the sources with the SDK. To verify, run ${ANDROID_SDK}/tools/android
Select the sources for the Android build targets you need.

Debug with framework source

At this point, you are ready to debug using the framework source. Highlight any framework code (like Activity, or Context) and hit Ctrl+B. It will take you to the source for that class. Sometimes documentation can be vague, and the definitive word is the source. You can also use the source to learn how canonical classes like ListView or DialogFragment are written. Looking at framework code is a very powerful way of learning good coding practices and system paradigms.

Happy hacking!

Monday, October 22, 2012

Expert C Programming: Deep C Secrets

I read a friend's copy of "Expert C Programming" many years ago, and ended up buying a copy for later reference. I didn't quite remember why I would purchase a book I had read already. Recently, I cracked open my copy for the first time: it still had the new book smell.

Oh, now I remember.

This is the most enjoyable programming book I have ever read.

The book is about corner cases and implementation-quirks of C, with a smattering of C++ thrown in. The entire book is divided into themes, and each theme is self-contained in a chapter. Each chapter talks about a quirk of the language, something that good C programmers should be aware of.  For example, one chapter talks about the differences between Kernighan&Ritchie C and ANSI C. Each idea is crisply presented, with source code and clear explanation. The chapters are littered with relevant anecdotes, historical background, and tantalizing puzzles.

Programming books can be dry and just about the facts. Recent technologies usually come with books that focus on how to get things done. While this is useful, it does not improve the appreciation of the technology. Expert C Programming was written 20 years after the development of the language. Perhaps time leads to some clarity and a light-hearted view of things.

Programming is more than just a profession: it is a creative process. It helps to have such books in your shelf: so you can them pick up and remind yourself how fun computing can be.


(Image courtesy: Amazon)