fillRect does not display anything?

[Ishmael]

Ok, I'm missing something simple here. For some reason, QPainter isn't displaying anything. I thought this code should simply fill the background of the scene with blue. Any ideas? This is the entirety of my code:

#include <QtGui>
 
int main(int argc, char **argv){
  QApplication app(argc, argv);
  QGraphicsView view;
  QGraphicsScene scene;
  view.setScene(&scene);
 
  QPainter painter;
 
  QRectF sceneRect = scene.sceneRect();
  painter.fillRect(sceneRect, Qt::blue);
 
  view.show();
  return app.exec();
}

#include <QtGui>

int main(int argc, char **argv){
  QApplication app(argc, argv);
  QGraphicsView view;
  QGraphicsScene scene;
  view.setScene(&scene);

  QPainter painter;
  
  QRectF sceneRect = scene.sceneRect();
  painter.fillRect(sceneRect, Qt::blue);

  view.show();
  return app.exec();
}

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[yogeshgokul]

You should use QPainter in PaintEvent only.
Here you can use scene.setBackgroundBrush(Qt::blue);
So now your code will look like :

#include <QtGui> 
int main(int argc, char **argv){
	QApplication app(argc, argv);
	QGraphicsScene scene;
	QGraphicsView view(&scene);
	scene.setBackgroundBrush(Qt::blue);
	view.show();
	return app.exec();
}

#include <QtGui> 
int main(int argc, char **argv){
	QApplication app(argc, argv);
	QGraphicsScene scene;
	QGraphicsView view(&scene);
	scene.setBackgroundBrush(Qt::blue);
	view.show();
	return app.exec();
}

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[Ishmael]

Thanks for the response. I think I oversimplified my example. Actually I'd like to be able to paint a filled rectangle anywhere on the screen, not necessarily just the background. What should I use instead of QPainter to do this?

[wysota]

You can't paint "anywhere on the screen" (meaning the desktop). You can only paint on widgets.

[Ishmael]

Oops, sorry. I meant to say "anywhere on the SCENE" (not SCREEN). Is this possible? I'd like to be able to superimpose simple drawings on the scene - it seemed like QPainter was supposed to do exactly that.

For that matter, maybe you have a better solution for my specific current problem. I'm trying to fill in the rectangle that contains a character (QSimpleTextItem - thanks wysota!). I am able to get a rectangle to appear around the item by doing the following

QRectF r = item->sceneBoundingRect();
scene->addRect(r);

QRectF r = item->sceneBoundingRect();
scene->addRect(r);

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but what I'd really like to do is display a filled rectangle. How do I do this?

[wysota]

The scene should be composed from items, so use items and forget drawing on the scene directly. It's possible but I don't think this is something you really want.