QPainter and QOpenGLWidget - Text Corruption

webzoid

This kinda follows on from this post from a few years back:

https://forum.qt.io/topic/64310/rendering-text-in-qopenglwidget

When attempting to use QPainter to draw some text from within the paintGL function of a QOpenGLWidget, some kind of corruption is occurring on the font glyphs:

This text should just say "Hello there" but clearly does not.

Within the paintGL function, I have the following code:

QPainter p(this);
p.setFont(QFont("Verdana", 16));
p.setPen(Qt::white);
p.setBrush(Qt::transparent);
p->drawText(500, 500, 100, 20, Qt::AlignCenter, "Hello there");

Any pointers would be greatly appreciated.

Christian Ehrlicher

When you're following this post then you're missing

painter.beginNativePainting();

but don't know if it help though.

webzoid

@Christian-Ehrlicher unfortunately I’ve already tried that and it makes zero difference.

mrjj

Hi
Using the code from the other post

#include <QApplication>
#include <QOpenGLWidget>
#include <QOpenGLFunctions>
#include <QPainter>

class MyOpenGLWidget : public QOpenGLWidget
{
public:
    MyOpenGLWidget() {}

    void initializeGL()
    {
        QOpenGLFunctions *f = QOpenGLContext::currentContext()->functions();
        f->glClearColor(1.f, 1.f, 1.f, 1.f);
    }

    void resizeGL(int w, int h)
    {
        QOpenGLFunctions *f = QOpenGLContext::currentContext()->functions();
        f->glViewport(0, 0, w, h);
    }

    void paintGL()
    {
        QOpenGLFunctions *f = QOpenGLContext::currentContext()->functions();

        f->glClear(GL_COLOR_BUFFER_BIT);

        QPainter painter(this);
        painter.setPen(Qt::black);
        painter.setFont(QFont("Arial", 56));
        painter.drawText(0, 0, width(), height(), Qt::AlignCenter, "Hello World!");
        painter.end();
    }
};

int main(int argc, char **argv)
{
    QApplication app(argc, argv);

    MyOpenGLWidget wnd;
    wnd.resize(400, 300);
    wnd.show();

    return app.exec();
}

alt text

Tried on win 10, win 7 and linux and had no text corruption.

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QPainter and QOpenGLWidget - Text Corruption