QPainter native painting in QImage

beecksche

Hi,
i try to paint into a QImage with native painting:

void paint(QPaintDevice *device)
{
    QPainter painter(device);
    painter.beginNativePainting();

    glBegin(GL_POINTS);
      glColor3f(1, 0, 0); glVertex3f(0, 0, 0);
      glColor3f(0, 1, 0); glVertex3f(1, 0, 0);
      glColor3f(0, 0, 1); glVertex3f(1, 1, 0);
      glColor3f(1, 1, 0); glVertex3f(0, 1, 0);
    glEnd;

    painter.endNativePainting();
}

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

    QImage image(100,100, QImage::Format_RGB32);
    paint(&image);
    bool ok = image.save("test.jpg"); // ok = true

    return 0;
}

But the image doesn't show the points. Do i forget something?

mrjj

@beecksche
Hi
Are you sure this can work ?
I mean, Qimage must have an openGL context for this to be even possible to work.

beecksche

@mrjj
I'am definitily not sure ;-).

I just saw, that the QPainter class paints into a QPaintDevice, and QImage is a QPaintDevice.
I was not sure if the QPainter class translates the raw OpenGL commands and "paints" them into the QPaintDevice.

So i will try it with a QWidget and see what happens :)

Edit:
So i tested the native painting:

First of all, if i want to do the native painting in separate function it has no effect at all. So I inherited a class by QWidget and override the paintEvent function. But also the native painting has no effect, unless i use the QOpenGLWidget as base class.

But here i don't understand the benefit, because you can use the functions described in the doc from QOpenGLWidget, paintGL and so on.