Development/Tutorials/Plasma4/GettingStarted

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    Revision as of 05:29, 8 July 2007 by Bgrolleman (talk | contribs) (→‎Abstract: - unable to upload .png files, linking as quick fix)
    Creating your first Plasmoid
    Tutorial Series   Plasma Tutorial
    Previous   C++, Qt, KDE4 development environment
    What's Next  
    Further Reading   CMake

    Abstract

    Where going to start creating a simple plasmoid in this tutorial, to keep things simple we will only create a static plasmoid, it will contain the following items.

    • SVG Background
    • Icon
    • Some nice text

    I seem to be unable to upload images to the wiki, example image

    The Code

    The .desktop file

    Every Plasmoid needs a .desktop file to tell plasma how they should be started, and what name they carry.

    plasma-applet-tutorial1.desktop [Desktop Entry] Encoding=UTF-8 Name=Tutorial 1 Comment=Plasma Tutorial 1 Type=Service ServiceTypes=Plasma/Applet

    X-KDE-Library=plasma_applet_tutorial1 X-KDE-PluginInfo-Author=Bas Grolleman [email protected] X-KDE-PluginInfo-Name=plasma_applet_tutorial1 X-KDE-PluginInfo-Version=0.1 X-KDE-PluginInfo-Website=http://plasma.kde.org/ X-KDE-PluginInfo-Category= X-KDE-PluginInfo-Depends= X-KDE-PluginInfo-License=GPL X-KDE-PluginInfo-EnabledByDefault=true

    The most important bits are the X-KDE-Library and X-KDE-PluginInfo-Name, they are the paste between your class and plasma, without it, nothing will start.

    The header file

    This is the example header file, I will add lot's of comment's in the code to explain everything.

    plasma-tutorial1.h // Here we avoid loading the header multiple times

    1. ifndef Tutorial1_HEADER
    2. define Tutorial1_HEADER

    // We need the Plasma Applet headers

    1. include <Plasma/Applet>

    // Define our plasma Applet class PlasmaTutorial1 : public Plasma::Applet {

       Q_OBJECT
       public:
           // Basic Create/Destroy
           PlasmaTutorial1(QObject *parent, const QStringList &args);
           ~PlasmaTutorial1();
    
           // This function returns the size of your applet
           QRectF boundingRect() const;
           // The paintInterface procedure paints the applet to screen
           void paintInterface(QPainter *painter, 
               const QStyleOptionGraphicsItem *option, QWidget *widget =0);
    

    };

    // This is the command that links your applet to the .desktop file K_EXPORT_PLASMA_APPLET(tutorial1, PlasmaTutorial1)

    1. endif

    QRectF boundingRect()

    The boundingRect() function tells plasma the actual size of the plasmoid, this is important because we need to know how much space is taken on screen.

    Tip
    If you have issues with your plasmoid leaving pixels behind when dragging this is almost always a result of a incorrect boudingRect()

    void paintInterface(...)

    You could call this the main function, since this paints the plasmoid on screen, here you define how you want your plasmoid to look.

    K_EXPORT_PLASMA_APPLET ( <name>, <class> )

    This is a small but very important part, this links your classname to the applet name in the .desktop file, if your applet doesn't seem to be loaded than chances are there is a difference between this and your .desktop file

    Tip
    The K_EXPORT_PLASMA_APPLET adds "plasma_applet_", please pay attention to this when setting up your .desktop file to avoid a name difference


    The actual work file

    Here is the body of the function, again with a lot of comments in between.

    plasma-tutorial1.cpp

    1. include "plasma-tutorial1.h"
    2. include <QPainter>
    3. include <QFontMetrics>
    4. include <KIcon>
    5. include <Plasma/Svg>

    PlasmaTutorial1::PlasmaTutorial1(QObject *parent, const QStringList &args)

       : Plasma::Applet(parent, args)
    

    { }

    PlasmaTutorial1::~PlasmaTutorial1() { }

    QRectF PlasmaTutorial1::boundingRect() const {

       // In this tutorial we use a fixed size
       return QRectF(0,0,128,128);
    

    }

    void PlasmaTutorial1::paintInterface(QPainter *p,

       const QStyleOptionGraphicsItem *option, QWidget *widget)
    

    {

       // First we create the objects to hold the icon and background image
       KIcon icon("document");
       Plasma::Svg* background = new Plasma::Svg("widgets/background",this);
       // Tell the Plasma/Svg object to use the whole image, 
       // instead of parts of it.
       background->setContentType(Plasma::Svg::SingleImage);
    
       // Now we draw the applet, starting with the background
       background->resize(boundingRect().width(),boundingRect().height());
       background->paint(p,boundingRect().left(),boundingRect().top());
    
       // The we place the icon and text
       p->drawPixmap(20, 0, icon.pixmap(boundingRect().width()-40));
       p->save();
       p->setPen(Qt::white);
       p->drawText(boundingRect(),Qt::AlignBottom+Qt::AlignHCenter,
           "Hello Plasmoid!");
       p->restore();
    

    }

    1. include "plasma-tutorial1.moc"