Opensourcedays 2012

I've just signed up for opensourcedays 2012 which is held this weekend.

I'm especially looking forward to the talks about Qt and KDE.

Maybe I'll see you there?

Tips! Kdenlive - A great video editor

I've just started to take a look on how to editing videos and was searching the net to find some tools for Linux.

After trying a couple I found out about the KDE application Kdenlive from some blog post and I must say that this tools looks very promising. It did crash once when I tried it out but I can live with that since I'm not a heavy user of video editing. I just need something for creating youtube videos occasionally.

In addition to the great app there's also a bunch of video tutorials here to help you getting started.

So if you're in the same position as me I think you should take a look at Kdenlive

Digikam - Light table

This post is somewhat related to the post about ctypes and gphoto.

Background
I consider myself a pre-amateur photographer and that means I'm taking a lot of shots just to learn how the camera works. I own a Canon EOS 1000D and have recently moved from the fully automatic exposure modes to the advanced exposure modes, and to be more specific, the programmed auto exposure mode.

So, I needed an application that could load a couple of pictures, showing two pictures side-by-side for visual comparison and at the same time presenting the more important meta-data attributes such as focal length, exposure time, ISO and aperture. I considered doing such application myself and that's why I came across and started to explore gphoto. But luckily, I managed to stop myself and took yet another look at what Digikam offers. I'm a die-hard KDE-fan and have been using digikam, which is a KDE photo manager application, for quite some time to organize my photos but never actually used any other features except removing red-eyes.

To my surprise digikam included exactly the feature I was looking for! It's called the Light Table.

The Light Table
Digikam allows you to select a couple of pictures which can be placed onto the light table, as shown in the screenshot below.

By choosing Place onto Light Table a new window is opened with, in this case, the three pictures loaded and two of them shown side-by-side.

The light table also displays the meta-data for the respective picture (sorry about that some of the attributes are in Swedish) that are currently shown. You can synchronize operations like zooming and panning. When you zoom, both pictures will be zoomed to the same level and when panning, both pictures will be panned to the same area, really nice.

This was exactly what I was looking for. Now I can take a couple of shots with different settings, for example, changing the white balance, ISO and/or other parameters and compare the result rather easily. I get both a visual and a meta-data diff in the same view.

I just wanted to share my findings and hope this post was to some use for others that are looking for something similar.

GMonitor

Ah, I've finally managed to make my new fresh Kubuntu 9.10 installation usable. Now it's time to do some KDE stuff and I'll show you how easy it's to create a plasmoid (applet/widget) for KDE4.

I've created a simple applet which shows the number of unread mail in a Gmail inbox. We already know how to fetch the list with unread mail, which I have explained in a previous blog post. Now I'll create a nice applet showing the count. I'm going to keep it as simple as possible, writing hard-coded values, skip error handling and so on to avoid making things more complicated than necessary.

There are several good tutorials at techbase.kde.org which explains plasma programming. They cover the basics and explains things in detail so I'll only make references to the pages instead of repeating what's already been written.

The first tutorial you should read (you don't have to read it right now, you can read it after you tried doing the applet) is Python Plasma Getting Started. The tutorial covers setting up a simple plasmoid, packaging, installing and running.

I'll name the plasmoid GMonitor because it only monitors the mailbox and shows the number of unread mail, it will not actually try to do some kind of notification (yet?!).

I've put the code on github, you can clone it with:

$ git clone git://github.com/mariob/gmonitor.git

You'll find a Makefile in the git which can be useful when doing plasmoids. The Makefile supports installing, un-installing, viewing, packaging and updating the plasmoid.

The directory tree looks like this:

gmonitor/
|-- Makefile
|-- README
|-- contents
|   `-- code
|       `-- main.py
`-- metadata.desktop

The gmonitor directory is the project home and contents/code contains the python source. The metadata.desktop file will be explained below.

To be able to install and run your applet you need to provide a metadata.desktop file to plasma. The metadata.desktop file contains important information about the applet and you can read more about the file in the Plasma Getting Started tutorial.

Feel free to change the file. The Name specifies the applet name and the Icon field gives the name to the icon to associated with this applet. These two fields are typically shown when listing applets in the 'Add Widget' dialog. There are two important fields which must be present for plasma to run your applet, the X-Plasma-API field specifies which script-engine to be used and the X-Plasma-MainScript field which script to be executed. It's also good to know that the X-KDE-PluginInfo-Name fields is used as a plasmoid identification, so it should be unique.

Some notes about the implementation. There are two classes, GMonitor and MailFrame (I know, poor name). The MaiFrame class has an icon and a label. When the mail count is set to zero (by calling setCount(cnt)), the icon is disabled, grayed and the label is set to 'No new mail'. When the mail count is set to a value greater than zero, the icon is enabled, colored and the label is set to 'Count: x', where x is the number of mail in the inbox. See the images below.

Sample of what the applet looks like

When the icon is enabled and clicked, a 'clicked()' signal is emitted. The GMonitor class connects the openBrowser() method to the 'clicked()' signal. The openBrowser() method opens a default browser in KDE to load the google mail url. The GMonitor also sets up a timer to fetch the feed in 60 second interval. The fetchFeed() method uses the KIO framework in KDE to download the content from a URL and parseFeed() parses the downloaded feed and emits a 'mailcount' signal.

The implementation depends on feedparser which can be installed on Ubuntu by running:

$ sudo aptitude install python-feedparser

You can also download and put the feedparser.py file inside the code directory.

Not that bad. It's actually possible to create a very simple 'good looking' Gmail monitor in less than 100 lines of code (excluding comments) with Python and KDE.

To view this plasmoid without installing it run (while standing in the gmonitor folder):

$ make view

This might only work on KDE4.3, not sure if the plasmoidviewer in 4.2 supports running plasmoids without first installing them. If it fails you should install the plasmoid and run plasmoidviewer yourself (or modify the makefile):

$ make install
$ plasmoidviewer pysnippet-gmonitor

If you never heard of Qt signals and slots you should read this introduction on the topic. For example, a button can 'emit' a signal when it's clicked. A slot (function/method) can be connected to a signal and each time the signal is emitted the function/method will be called.

You can find the Python KDE4.3 API docs here. Unfortunately, I don't find them as good as the Qt docs.

When running the applet, KDE will ask for the username/password when it tries to connect to Google. You can check the 'remember the password' checkbox which will make KDE cache the password as long as the desktop session is alive. If you choose not to, you'll have to enter your username/password each time the code tries to fetch the feed. A better solution is to use KWallet.

Ok, hope you enjoyed it and start doing cool plasmoids!

Kubuntu 9.10

I've installed Kubuntu 9.10 and I'm busy configuring it to a usable state. For the moment I don't have too much spare time but I'm almost done.

I hope I'll have time to do a post about creating plasmoids (KDE4 desktop widgets) in the next couple of days. I think I'll do a gmonitor applet which will show the number of unread mail in your Gmail inbox.

KDE Hello World

I have plans to do a web radio player (I wonder if we'll ever see this app). My intention is to learn Qt/KDE programming in Python. I've played around with Qt a bit and I'm starting to get comfy. I've decided to try doing the player as a KDE app, just to learn more about KDE. Qt is great for doing cross-platform stuff but I want to take a look at what KDE offers on top of Qt. You can find docs, tutorials and more on KDE TechBase. The following snippet shows the minimum amount of code needed to create a typical KDE app in Python.

from PyKDE4 import kdecore
from PyKDE4 import kdeui
import sys

def createAboutData():
    """
    Create a KAboutData with information about this application.
    """
    return kdecore.KAboutData(
            # Program name used internally
            "hello",
            
            # Catalog name
            "",                       
            
            # Displayable program name
            kdecore.ki18n("Hello World app"),
            
            # Program version
            "0.1.0",
            
            # Short description about the program
            kdecore.ki18n("A simple KDE Hello World app"),
            
            # Program license
            kdecore.KAboutData.License_BSD,
            
            # Copyright statement
            kdecore.ki18n ("(c) 2009 Mario Boikov"),
            
            # Free form text
            kdecore.ki18n("Free form text\nsupporting newlines"),
            
            # Home page address for this program
            "http://www.pysnippet.com",
            
            # Bug report email address
            "mario@beblue.org",
            )

def main():
    about = createAboutData()
    kdecore.KCmdLineArgs.init(sys.argv, about)

    app = kdeui.KApplication()

    # INSERT APP CODE HERE

    # Start event loop
    sys.exit(app.exec_())

if __name__ == '__main__':
    main()

Nothing special will happen if you execute this application, we need some kind of window/widget to display something. To accomplish this we can create a KMainWindow with a KPushButton. We'll also add code to print Hello World when the button is clicked. The following snippet will create a window with a push button:

from PyKDE4 import kdeui
from PyKDE4 import kdecore
from PyQt4 import QtCore

class MainWindow(kdeui.KMainWindow):
    def __init__(self):
        super(MainWindow, self).__init__()

        # Create widget with vertical box layout manager
        layout = kdeui.KVBox()

        # Create push button and add to layout
        button = kdeui.KPushButton(kdecore.i18n("Push Me!"), layout)

        # Connect to button's 'clicked' signal 
        QtCore.QObject.connect(button, QtCore.SIGNAL("clicked()"),
                               self.buttonClicked)

        self.setCentralWidget(layout)

    def buttonClicked(self):
        print "Hello World!"

You might wonder why I use ki18n() when creating the KAboutData and i18n() for the MainWindow. Both functions do translations, i18n() requires an instance of KApplication before use but ki18n() don't.

To actually show the window we have to instantiate it and make it visible, the "INSERT APP CODE HERE" comment should be replaced with the following lines:

    mainWindow = MainWindow()
    mainWindow.show()

As you can see, it doesn't take too much effort to create a simple app in KDE. There's almost more code to create the KAboutData than doing the window with a push button. Here's a screen shot of what the window looks like on my Kubuntu installation:

If we compare Qt and KDE there aren't too much differences, at least with this example. The code below implements the same Hello World app made with Qt:

import sys
from PyQt4 import QtCore, QtGui

class MainWindow(QtGui.QMainWindow):
    def __init__(self, title):
        super(MainWindow, self).__init__()
        self.setWindowTitle(title)

        centralWidget = QtGui.QWidget()

        button = QtGui.QPushButton("Push Me!")

        layout = QtGui.QVBoxLayout()
        layout.addWidget(button)

        centralWidget.setLayout(layout)

        QtCore.QObject.connect(button, QtCore.SIGNAL("clicked()"),
                               self.buttonClicked)

    self.setCentralWidget(centralWidget)

    def buttonClicked(self):
        print "Hello World!"

def main():
    app = QtGui.QApplication(sys.argv)

    mainWindow = MainWindow("Hello World App")
    mainWindow.show()

    sys.exit(app.exec_())

if __name__ == "__main__":
    main()

The biggest difference is how the layout is handled and the absence of About Data.