Set opacity in Linux

Hello!

I want to add some "fading" effect (I guess that's the name) in a pop-up widget in one of my applications for Linux when the widget is both shown and hidden. I'ld guess that the normal way of doing this is to add a QPropertyAnimation that would change the window's opacity from 0 to 255 in a period of time (lets say 500 ms).

Now the problem is that in the Linux I'm using window opacity is not available; so I both can't change the window opacity with QProperyAnimation, nor with setWindowOpacity(qreal).


The question: how do I do this, then? I tried with stylesheet (connecting a slot to the QProperyAnimation and changing the window's background-color alpha channel from 0 to 255) but it doesn't seem to be interesting setting a new stylesheet so quickly (calling a set QString method frequently), nor is it elegant.

I wonder if there is another way of doing this for this circumstance that is not by stylesheet?


I'm glad for any help,

Momergil


Note: using Qt 4.8 for ARM

Quote:

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Originally Posted by Momergil

Now the problem is that in the Linux I'm using window opacity is not available

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Yes, it is.

Just tried with

Code:

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#include <QApplication>
#include <QLabel>
#include <QPropertyAnimation>
 
int main(int argc, char ** argv)
{
    QApplication app(argc, argv);
 
    QLabel label("Hello World");
 
    label.show();
 
    QPropertyAnimation fade(&label, "windowOpacity");
    fade.setStartValue(1.0);
    fade.setEndValue(1.0);
    fade.setKeyValueAt(0.5, 0.0);
    fade.setDuration(5000);
 
    fade.start();
 
    return app.exec();
}

---

A window with the label in it appears, fades out and fades in again.

Cheers,
_

Hello anda_skoa!

First, thanks for the reply.

Second, I was quite interested when you provided a direct use of QPropertyAnimation as a solution to my problem, since (as I mentioned above) I've tried that solution before without success. I decided to give a try, nonetheless, and for my surprise your code actually worked.

I began to make comparisons between your QPropertyAnimation implementation and mine (having done the proper adaptations) and despite various checkings and debugs, I simply couldn't make my code work; the fade effect simply don't happen.

So the code I'm using is below. As you may see, it's supposed to be a replacement of QMessageBox that is activated once the user clicks in a place, when the show1() method is called. It should than start the fade effect on poBaseWidget, and once the user clicks on it, a new closing fade should occur. Could you please tell me why it's not working?

Thanks,

Momergil

Code:

---

class MessageFrame : public QFrame
{
    Q_OBJECT
    Q_PROPERTY(QString currentText READ currentText WRITE setCurrentText)
    Q_ENUMS(Icon)
    Q_ENUMS(TextType)
 
public:
    enum Icon { Question, Information, Warning, Critical };
    enum TextType { ScreenDescription, GeneralText };
 
    MessageFrame(QWidget* parent = 0) :
        QFrame(parent),
        poBaseWidget(new QFrame(this))
    {
        setObjectName("MessageFrame");
        setGeometry(0,20,800,460);
 
        //
        poBaseWidget->setGeometry(120,0,560,100);
        poBaseWidget->setStyleSheet("* { background-color: rgb(192,192,192);"
                                    "background-origin: content;"
                                    "border: 2px rgb(128,128,127);"
                                    "border-radius: 10px; }");
 
        //
        iconLabel = new QLabel(poBaseWidget);
        iconLabel->resize(32,32);
        setIcon(Information);
 
        //
        textLabel = new QLabel(poBaseWidget);
        textLabel->setWordWrap(true);
        textLabel->setMaximumSize(textLabel->parentWidget()->width() - iconLabel->width() - 20, textLabel->parentWidget()->height() - 10);
        textLabel->resize(textLabel->maximumSize());
 
        //
        startFadeAnimation = new QPropertyAnimation(poBaseWidget, "windowOpacity",this);
        startFadeAnimation->setStartValue(0.0);
        startFadeAnimation->setEndValue(1.0);
        startFadeAnimation->setDuration(5000);
 
        stopFadeAnimation = new QPropertyAnimation(poBaseWidget, "windowOpacity",this);
        stopFadeAnimation->setStartValue(1.0);
        stopFadeAnimation->setEndValue(0.0);
        stopFadeAnimation->setDuration(5000);
 
        connect(stopFadeAnimation,SIGNAL(finished()),this,SLOT(close()));
 
        //
        poBaseWidget->installEventFilter(this);
 
        hide(); //hide();
    }
 
    virtual ~MessageFrame()
    {
        poBaseWidget->removeEventFilter(this);
    }
 
    inline QString currentText() const;
 
    void setCurrentText(const QString& text);
 
    void setIcon(const Icon icon);
 
    static void information(const QString& text);
 
    static void warning(const QString& text);
 
    static void critical(const QString& text);
 
private:
    QLabel* textLabel,
          * iconLabel;
    QPropertyAnimation* startFadeAnimation,
                      * stopFadeAnimation;
    QString screenText;
    QFrame* poBaseWidget;
 
protected:
    bool eventFilter(QObject *obj, QEvent *ev)
    {
        if (obj == poBaseWidget && ev->type() == QEvent::MouseButtonRelease)
        {
            stopFadeAnimation->start();
            return true;
        }
        else
            return QFrame::eventFilter(obj,ev);
    }
 
public slots:
    void show1(const TextType type = GeneralText)
    {
        switch (type)
        {
            case GeneralText: //last set text
                break;
 
            case ScreenDescription:
//                setCurrentText(screenText);
                break;
        }
 
        show();
 
        startFadeAnimation->start();
    }
 
    inline void setScreenText(const QString& text)  { screenText = text; }
 
    /////////////////////////////////////////////////////
    /// SINGLETON STUFF - DON'T TOUCH
public:
    static void start(QWidget* parent = 0);
 
    static void MessageFrameDestroy();
 
    inline static MessageFrame& instance();
 
private:
    static MessageFrame* poInstance;
};

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You are animating windowOpacity of poBaseWidget instead of your MessageFrame instance. Only top-level windows can have their windowOpacity manipulated.

Quote:

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Originally Posted by wysota

You are animating windowOpacity of poBaseWidget instead of your MessageFrame instance. Only top-level windows can have their windowOpacity manipulated.

---

Oh, I remember reading that in the manual; I didn't noticed I was doing that in my code. Anyway, why is that so? And, well, if the method show by anda_skoa is valid only for top-level windows, I'll restate my first question to: is there a way to create such a "fade" effect that is not by stylesheet and that is valid for any widget I want to apply the effect regardless of being a top level widget or not?

So you want the content of the window to fade, not the window itself?

Maybe usingQGraphicsOpacityEffect on the widget which you want to fade.

Cheers,
_

Quote:

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Originally Posted by anda_skoa

So you want the content of the window to fade, not the window itself?

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Exactly, and your suggestion worked perfectly. Thanks!

Momergil