Qt 6.6.1 WebAssembly. Background color of parent window is changed to black

[8Observer8]

Hi,

I have a main window to place an OpenGL widget on it Background color of parent window is changed to black:

main.cpp

#include <QtGui/QOpenGLFunctions>
#include <QtOpenGLWidgets/QOpenGLWidget>
#include <QtWidgets/QApplication>
#include <QtWidgets/QLabel>
#include <QtWidgets/QVBoxLayout>
#include <QtWidgets/QWidget>

class OpenGLWidget : public QOpenGLWidget, private QOpenGLFunctions
{
    Q_OBJECT

private:
    void initializeGL() override
    {
        initializeOpenGLFunctions();
    }

    void paintGL() override
    {
        glClearColor(0.1f, 0.3f, 0.2f, 1.f);
        glClear(GL_COLOR_BUFFER_BIT);
    }
};

class MainWindow : public QWidget
{
    Q_OBJECT

public:
    MainWindow()
    {
        setWindowTitle("OpenGL, Qt6, C++");
        resize(300, 300);

        m_nameLabel = new QLabel("Click on object or background");
        m_nameLabel->setSizePolicy(QSizePolicy::Policy::Fixed, QSizePolicy::Policy::Fixed);
        OpenGLWidget *openGLWidget = new OpenGLWidget();

        QVBoxLayout *layout = new QVBoxLayout();
        layout->addWidget(m_nameLabel);
        layout->addWidget(openGLWidget);
        // layout->addStretch();
        setLayout(layout);
    }

private:
    QLabel *m_nameLabel;
};

#include "main.moc"

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

pro

QT += core gui openglwidgets widgets

win32: LIBS += -lopengl32

CONFIG += c++17

SOURCES += \
    main.cpp

TARGET = app

But it works without the problem on Desktop:

And on physical device with Android:

Cross-ref: https://stackoverflow.com/questions/77736353/qt-6-6-1-webassembly-background-color-of-parent-window-is-changed-to-black

[8Observer8]

If I don't add the openGLWidget:

        QVBoxLayout *layout = new QVBoxLayout();
        layout->addWidget(m_nameLabel);
        // layout->addWidget(openGLWidget);
        layout->addStretch();
        setLayout(layout);

the color is normal:

[8Observer8]

I created the bug report: https://bugreports.qt.io/browse/QTBUG-120651

[andrew22]

@8Observer8 Did you find a workaround for this problem?

[8Observer8]

@andrew22 I sure it is a bug of Qt and only Qt developers can solve it. I made a bug report: https://bugreports.qt.io/browse/QTBUG-120651 I attached an example in a zip there.

I found a solution of the second problem: https://bugreports.qt.io/browse/QTBUG-120956 When you resize a window it will be completely black. You should call glClearColor() in the paintGL() method like this:

    void paintGL() override
    {
        glClearColor(0.1f, 0.3f, 0.2f, 1.f);
        glClear(GL_COLOR_BUFFER_BIT);
    }

You can upload WebAssembly files to sandboxes, like replit.com and an app can be running by one click: https://replit.com/@8Observer8/background-color-of-parent-window-opengl-qt6-cpp

[andrew22]

@8Observer8 Thank you for your response. I'll keep an eye on the bug report.