How to make WA_TranslucentBackground work on Windows without using FramelessWindowHint? - c++

Question

Im using setAttribute(Qt::WA_TranslucentBackground); to make my QMainWindow background transparent, however, this attribute only work if:
I also set: setWindowFlag(Qt::FramelessWindowHint);
or, have at least one QOpenGLWidget in my GUI.
I have no experience with QOpenGlWidget, i wonder if its possible to use QSurfaceFormat or something like, to achieve the same 'thing' QOpenGL does when added to a QMainWindow, that makes the attribute work.
Or if there's any other 'option' than setting the FramelessWindowHint flag or creating an QOpenGL widget.
Example code:
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
/*
QSurfaceFormat format;
format.setAlphaBufferSize(8);
QSurfaceFormat::setDefaultFormat(format);
QSurfaceFormat format;
format.setAlphaBufferSize(8);
format.setSamples(16);
format.setSwapBehavior(QSurfaceFormat::DoubleBuffer);
format.setRenderableType(QSurfaceFormat::OpenGL);
format.setProfile(QSurfaceFormat::CoreProfile);
QSurfaceFormat::setDefaultFormat(format);
*/
MainWindow w;
w.show();
return a.exec();
}
//mainwindow.h
#include <QtWidgets/QMainWindow>
#include "ui_MainWindow.h"
QT_BEGIN_NAMESPACE
namespace Ui { class MainWindowClass; };
QT_END_NAMESPACE
class MainWindow : public QMainWindow{
Q_OBJECT
public:
MainWindow(QWidget* parent = nullptr);
}
//mainwindow.cpp
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent), ui(new Ui::MainWindowClass())
{
ui->setupUi(this);
setAttribute(Qt::WA_TranslucentBackground);
QGridLayout* layout = new QGridLayout();
ui->centralWidget->setStyleSheet("background-color: transparent;");
ui->centralWidget->setLayout(layout);
QWidget* widget = new QWidget(this);
widget->setStyleSheet("background-color: green; border-radius: 32px;");
layout->addWidget(widget);
//QOpenGLWidget* opengl = new QOpenGLWidget(this);
//opengl->deleteLater();
}
Creating the QOpenGlWidget and calling opengl->deleteLater() the WA_TranslucentBackground works, however, it make the application use 50mb more of ram compared to not creating the QOpenGLWidget.
This is not much if i were creating just one GUI, but I'm creating multiples.

Answer 1

Why not try setting the opacity level of the window by changing the windowOpacity property using setProperty?
Example:
YourWindow->setProperty("windowOpacity", 0.0);
Setting the opacity level to 0 results in a transparent background