Frameless and transparent window

Question

I want to open a frameless and transparent window when I click a button.

I've got a new window to open up when I press a button, but I can't seem to get the frameless and transparent part working.

main.cpp:

#include "learnwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    LearnWindow w;
    w.show();
    
    return a.exec();
}

Main window header file:

#ifndef LEARNWINDOW_H
#define LEARNWINDOW_H

#include <QMainWindow>
#include <transwindow.h>

namespace Ui {
class LearnWindow;
}

class LearnWindow : public QMainWindow
{
    Q_OBJECT
    
public:
    explicit LearnWindow(QWidget *parent = 0);
    ~LearnWindow();
    
private slots:
    void on_pushButton_clicked();

private:
    Ui::LearnWindow *ui;
    TransWindow *winTrans;

public slots:
    void openTrans();
};

#endif // LEARNWINDOW_H

Main window source file:

#include "learnwindow.h"
#include "ui_learnwindow.h"

LearnWindow::LearnWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::LearnWindow)
{
    ui->setupUi(this);
}

LearnWindow::~LearnWindow()
{
    delete ui;
}

void LearnWindow::openTrans()
{
    winTrans = new TransWindow (this);
    //winTrans->setWindowTitle("NewWin");
   // winTrans->setWindowFlags(Qt::FramelessWindowHint | Qt::X11BypassWindowManagerHint);
    //winTrans->setAttribute(Qt::WA_TranslucentBackground,true);
    //winTrans->setAutoFillBackground(false);
    //winTrans->setStyleSheet("background:transparent;");
    winTrans->show();
}

void LearnWindow::on_pushButton_clicked()
{
    openTrans();
}

Transparent window header file:

#ifndef TRANSWINDOW_H
#define TRANSWINDOW_H

#include <QDialog>

namespace Ui {
class TransWindow;
}

class TransWindow : public QDialog
{
    Q_OBJECT
    
public:
    explicit TransWindow(QWidget *parent = 0);

    //setWindowFlags(windowFlags()| Qt::FramelessWindowHint);

    ~TransWindow();
    
private:
    Ui::TransWindow *ui;
};

#endif // TRANSWINDOW_H

Transparent window source file:

#include "transwindow.h"
#include "ui_transwindow.h"

TransWindow::TransWindow(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::TransWindow)
{
    //setWindowTitle("NewWin");
    //setWindowFlags(Qt::FramelessWindowHint);
    //setAttribute(Qt::WA_TranslucentBackground,true);
    ui->setupUi(this);
}

TransWindow::~TransWindow()
{
    delete ui;
}

The commented out lines are the different things I tried.

If set Qt::FramlessWindowHint, the program runs normally, but never opens a new window when I click the button.

If I set Qt::WA_TranslucentBackground, the new window will open up when the button is pressed, but the background of the new window is black, not transparent.

I am using:

• Ubuntu 12.04
• Qt 5.0.2 (64-bit)
• Qt creator 2.7.1

Answer 1

Try this:

setWindowFlags(Qt::Widget | Qt::FramelessWindowHint);
setParent(0); // Create TopLevel-Widget
setAttribute(Qt::WA_NoSystemBackground, true);
setAttribute(Qt::WA_TranslucentBackground, true);  
setAttribute(Qt::WA_PaintOnScreen); // not needed in Qt 5.2 and up