Qt 4.8, Screenshot of large QGraphicsScene - qt

Question

I have QGraphicsScene, which size is 62450x4750. Somethimes I need to make screenshot of whole scene and save it to file. I tried like this:
QPixmap wholeScene(scene.sceneRect().size().toSize());
{
QPainter wholeScenePainter(&wholeScene);
scene.render(&wholeScenePainter);
}
// saving pixmap
or
QPixmap wholeScene(scene.sceneRect().size().toSize());
{
QPainter wholeScenePainter(&wholeScene);
int x = 0;
int portion = 32768; //
while( x < scene.sceneRect().width()) {
int width = scene.sceneRect().width() - x > portion ? portion : scene.sceneRect().width() - x;
QRect rect(x, 0, width, scene.sceneRect().height());
scene.render(&wholeScenePainter, rect, rect);
x += width;
}
}
// saving pixmap
or
QPixmap wholeScene(scene.sceneRect().size().toSize());
{
QPainter wholeScenePainter(&wholeScene);
int x = 0;
int portion = 4096;
while( x < scene.sceneRect().width()) {
int width = scene.sceneRect().width() - x > portion ? portion : scene.sceneRect().width() - x;
QRect rect(x, 0, width, scene.sceneRect().height());
QPixmap temp(rect.size());
QPainter p(&temp);
scene.render(&p, QRect(0, 0, rect.width(), rect.height()), rect);
wholeScenePainter.drawPixmap(x,0, temp);
//temp.save(QString("print%1.png").arg(QString::number(x)), "PNG");
x += width;
}
}
// saving pixmap
But every time I get the Image(Pixmap) cuted by width on 32768 px.

Answer 1

According to the documentation, QPainter does not support coordinates larger than +/- 32768. This does not appear to be fixed in Qt 5 either.
Maybe you can solve this by rendering the scene in multiple passes, e.g. through translation and clipping. You can render the scene in multiple blocks of max 32768x32768 pixels and put them in the proper position in the final image.