qt_draw_image.cpp

#include <QtWidgets>

static uchar pixel_buffer[512 * 512 * 4];

class MyWidget : public QWidget {
    Q_OBJECT

private:
    QImage * _image = nullptr;

public:
    MyWidget() {
        resize(512, 512);
        setWindowTitle(tr("My App"));
        memset(pixel_buffer, 0, sizeof(pixel_buffer));
        _image = new QImage(pixel_buffer, 512, 512, QImage::Format_RGB32);
    }

  protected:
    void paintEvent(QPaintEvent *event) override {
        QPainter painter(this);
        painter.drawImage(0, 0, *_image);
    }
};

int main(int argc, char **argv) {
    QApplication app(argc, argv);
    MyWidget v;
    v.show();
    return app.exec();
}

#include "qt_draw_image.moc"