QWebEngineView - black background QMainWindow

sepera_okeq

Hello there! I found a problem. Without QWebEngineView, the transparency made to create a shadow works fine for me, because my application is FramelessWindowHint.

or (to show that there is a shadow):

But with QWebEngineView, the place where transparency used to be is now filled with black for some reason.

I tried to use the solution that was presented here: https://stackoverflow.com/questions/43150506/opacity-not-working-with-qwebengineview-and-translucent-background

But, it didn't really help, and the black area is not acceptable for me. Thank you in advance!

sepera_okeq

I decided to make a separate project for testing this thing

Checking how transparency works with WebEngineView:

Source code:
main.cpp

#include "mainwindow.h"

#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.setWindowFlags(Qt::FramelessWindowHint);
    w.show();
    return a.exec();
}

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

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

    setAttribute(Qt::WA_TranslucentBackground);
    setAutoFillBackground(true);
    ui->centralwidget->setAttribute(Qt::WA_TranslucentBackground);
    ui->webEngineView->setAttribute(Qt::WA_TranslucentBackground);
    ui->webEngineView->setStyleSheet("background:transparent");
    ui->webEngineView->page()->setBackgroundColor(Qt::transparent);
    ui->webEngineView->setUrl(QUrl("https://google.com"));
}

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

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private:
    Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

mainwindow.ui
(where the white rectangle is a QWighet converted to a QWebEngineView)

When I deleted this wighet and deleted 4 lines of code( where WebEngineView is present), everything worked for me and it is transparent. Is it possible that this is a bug with QWebEngineView, which for some reason affects the style of the entire MainWindow?