I’m trying to play with QOpenGLFramebufferObject to see how could it affect the performance of an app I’m working on.

I have a QOpenGLFramebufferObject fbo that I use like this to draw a simple line:

void Example::drawLine() {
    fbo->bind();
    glBegin(GL_LINES);
    glVertex2f(0, 0);
    glVertex2f(100, 100);
    glEnd();
    fbo->release();
}

If I convert the framebuffer object to an image and display this image in the widget, the line is displayed correctly:

void Example::paintGL() {  // This implementation works.
    drawLine();

    QPainter painter(this);
    painter.beginNativePainting();
    auto im = fbo->toImage();
    painter.drawImage(QPoint(0, 0), im);
    painter.endNativePainting();
}

However, if I try to use textures (and from my understanding, I should use textures if performance matters), then the widget doesn’t display anything:

void Example::paintGL() {  // This one doesn't display anything.
    drawLine();

    fbo->bind();
    glBindFramebuffer(GL_FRAMEBUFFER, fbo->handle());
    glBindTexture(GL_TEXTURE_2D, fbo->texture());

    glEnable(GL_TEXTURE_2D);
    glBegin(GL_QUADS);
    glTexCoord2f(0.0f, 0.0f); glVertex2f(-1.0f, -1.0f);
    glTexCoord2f(1.0f, 0.0f); glVertex2f( 1.0f, -1.0f);
    glTexCoord2f(1.0f, 1.0f); glVertex2f( 1.0f,  1.0f);
    glTexCoord2f(0.0f, 1.0f); glVertex2f(-1.0f,  1.0f);
    glEnd();
    glDisable(GL_TEXTURE_2D);
    glBindFramebuffer(GL_FRAMEBUFFER, 0);

    fbo->release();
}

What am I missing?

(Note: I simplified the piece of code to be easier to read; in the actual code, I do extra checks for glGetError, and I do verify that bind and release return true.)