The KDE login Manager

The login manager is the “insert password” dialog that gets in the way when you want to use your computer. Of course you may not be the only user of the machine, so it’s somewhat needed when you share the seat. Some facts:

Kdm Top to Bottom

Qml to the rescue!

What if we throw away (or keep for “retro-compatibility”) the classic and themer frontends and just add a frontend using QML? This is the name of the language of the Qt Declarative module, that has just seen the light and will be merged into Qt for the 4.7 release.

Imagine this:

• theme creators will have 100X or more expressive power: make snow! login via a tetris puzzle! bounce my webcam picture!
• there will be animated themes (for login, user change, logout, etc..) or simple ones for more ‘classic’ kind of people
• kdm only needs to add a couple of bindings to the qml runtime, like functions for logging in and shutting down / suspend the system
• there is no need for compiled binaries, packages will be interpreted by the qml runtime – finally a painless get-hot-new-stuff (compared to plasma widgets, at least).

Conclusion

note for planetkde readers: check the original article to see the video!

I confess, I’m addiQted. You obviously think it’s normal (you’re not reading this blog by accident, aren’t you?) but it wasn’t always like this: I’ve liked some previous versions, but the upcoming Qt 4.6 really rocks!

The Fotowall case

As I shown previosly, Fotowall already uses some features of Qt 4.6. How much?
Qt 4.6 is referenced in 32 places, for example in snippets like this:

    // center the path
    QPointF pathCenter = path.boundingRect().center();
    #if QT_VERSION >= 0x040600
        path.translate(-pathCenter);
    #elif QT_VERSION >= 0x040500
        path = QTransform::fromTranslate(-pathCenter.x(), -pathCenter.y()).map(path);
    #else
        QTransform tx;
        tx.translate(-pathCenter.x(), -pathCenter.y());
        path = tx.map(path);
    #endif

From simple path translations to more complex property manipulations, everything got better. See this code snipped about extending QGraphicsObject in 4.6 versus 4.5 and 4.4.

    #if QT_VERSION >= 0x040600
    class AbstractContent : public QGraphicsObject
    #else
    class AbstractContent : public QObject, public QGraphicsItem
    #endif
    {
        Q_OBJECT
    #if QT_VERSION < 0x040600
        Q_PROPERTY(QPointF pos READ pos WRITE setPos)
        Q_PROPERTY(qreal rotation READ rotation WRITE setRotation NOTIFY rotationChanged)
    #endif
    #if QT_VERSION < 0x040600 && QT_VERSION >= 0x040500
        Q_PROPERTY(qreal opacity READ opacity WRITE setOpacity)
    #endif

Do you feel the pain?

I Need it

I need a world with Qt 4.6 only, because:

• It’s too much of a pain to support older versions in the same codebase
• It’s not even fair, because non-4.6 users won’t enjoy the program as it’s meant to be
• I can’t use A TON of new features because they’ll either simplify too much the code, or just because they don’t have a pre-4.6 equivalent
• and because I’d like to finally use
  • QGraphicsEffect for Fotowall’s content
  • QVector3D to say goodbye to enricomath.h
  • QGesture for multi-finger interaction
  • QPropertyAnimation to its full potential!

More 4.6 TEASING

1. As you seem to like videos, here is a preview of something we’re working on for Amarok Qt 4.6 only!!
   
2. Also, since I’m soooo much a giver, see the new Fotowall’s Word Cloud feature, coming in 0.9

See you @ Munich

I’m packing for the DevDays 2009 Munich. See you there

Seven days after the release of the Tech Preview 1, we released the latest stable Windows build of Fotowall [1] that was based on Qt 4.6. Somebody could argue that this is a bit imprudent. We did that because the benefits of the 4.6 release are worth the risk of the move!

Indirect Benefits, or ‘what you get for free’

• Improved quality and better speed in the OpenGL QPainter
• Better speed in the GraphicsView framework

Direct Benefits

• Animation Framework: this simply r0cks! I don’t know about the whole Kinetic stuff, I just mean the ability to create simple property animations.
  I don’t have a video to show you but just take a look at the Fotowall’s Top-Bar, the tabs appear and disappear with a nice and smooth grow-shrink animation, that make the program look soo 2009-ish! finally!
• QNetworkReply::isFinished(): thanks to this method I could implement a smart time-saver: when the user starts to drag a flickr picture, Fotowall starts downloading it. It can happen that, upon drop, the content has already been completely downloaded (so it can be placed in the canvas) or partially downloaded (so the used only needs to wait for the missing percent)

Drawbacks

• There are some graphics glitches when animating the opacity property of a QGaphicsProxyWidget (in OpenGL)
• Even by setting the QGraphicsItem::ItemSendsGeometryChanges flag, the previous behavior is not perfectly restored (we used itemChange, and the new behavior doesn’t allow Fotowall’s mirrors to sync properly to the objects)

Movie Time!

I’ve tried hard to record a screencast about the Cuteness & Performance of Qt 4.6, but in the end I had to use my camera.

Thanks Nokia for this great release!

[1] Fotowall is a creative program to mix local and online graphics content and build original work.

Update: the source code is included in the Fotowall project. The files you’re looking for are the ColorPickerItem ones.

Say you’re writing an application and you want to let the user to change the color of an item; what will you do?

The standard approach is to popup a color dialog with the standard HSV selector and all the sliders and values and buttons and confusion. Another approach is to pop down a combobox with a selection of default colors where the user won’t find the colour she is looking for (unless it’s RED, of course ).
Both approaches need you to get shocked by another window appearing right in front of you, so you loose the context and move the mouse far away from where it was.

Let’s take a look at this new approach:

The 2d (yet perspective transformed) dialog smoothly fades in when hovering the color and your favorite hue is just 1 or 2 clicks apart!