QOpenGLWidget and transparency

[Flassie]

Hi. I have problems with QOpenGLWidget and transparency. Here is my code:

#include <QApplication>
#include <QOpenGLWidget>
#include <QOpenGLFunctions>
#include <QOpenGLFunctions_4_3_Core>

#include <QDebug>

class OpenGLWidget : public QOpenGLWidget
{
public:
    OpenGLWidget(QWidget *parent = 0, const QColor color = QColor(255, 175, 75))
        : QOpenGLWidget(parent)
    {
        QSurfaceFormat format;
        format.setVersion(4, 3);
        format.setRedBufferSize(8);
        format.setGreenBufferSize(8);
        format.setBlueBufferSize(8);
        format.setAlphaBufferSize(8);
        format.setSamples(8);
        setFormat(format);
        this->create();
        m_color = color;
    }

protected:
    void initializeGL() {
        QOpenGLFunctions_4_3_Core *f = QOpenGLContext::currentContext()->versionFunctions<QOpenGLFunctions_4_3_Core>();
        qDebug() << m_color;

        f->glClearColor(m_color.redF(), m_color.greenF(), m_color.blueF(), m_color.alphaF());
    }

    void paintGL() {
        auto f = QOpenGLContext::currentContext()->versionFunctions<QOpenGLFunctions_4_3_Core>();
        f->glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    }

    void resizeGL(int w, int h) {
        auto f = QOpenGLContext::currentContext()->versionFunctions<QOpenGLFunctions_4_3_Core>();
        f->glViewport(0, 0, w, h);

    }

private:
    QColor m_color;
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    OpenGLWidget w;
    w.show();
    w.setMinimumSize(800, 600);

    OpenGLWidget w2(&w, QColor(125, 125, 125, 1));
    w2.setAttribute(Qt::WA_TranslucentBackground);
    w2.setGeometry(w.width()/2 - 40, w.height()/2 - 40, 80, 80);
    w2.show();

    return a.exec();
}

When I'm creating second widget (w2) I'm settings it's alpha to 1 (doesn't matter if I will set it to 0, or 100, or 255) but it looks like as it has 255. How can I solve this problem?

I'm using Qt 5.5, mingw32 and windows 10

[Flassie]

I don't believe that noone had the same problem and didn't solved it

[DavidArmand]

Hi,

It is a limitation.

http://doc.qt.io/qt-5/qopenglwidget.html

"Limitations
Putting other widgets underneath and making the QOpenGLWidget transparent will not lead to the expected results: The widgets underneath will not be visible. This is because in practice the QOpenGLWidget is drawn before all other regular, non-OpenGL widgets, and so see-through type of solutions are not feasible. Other type of layouts, like having widgets on top of the QOpenGLWidget, will function as expected."

You have to use Qt::WA_AlwaysStackOnTop to do this.