Drawing grids efficiently in QGraphicsScene

[Gopala Krishna]

Hi,
I need to draw grids in my app. The problem now is performance. The components move jerkily after adding grids. I confirmed from the profiler that scene::drawBackground() was most cpu consuming method.
Can anyone please help me out ? Is there any techinique like caching or something ?
Here is my code

void SchematicScene::drawBackground(QPainter *p, const QRectF& crect)
{
      const QRectF rect = crect.normalized();
   p->save();
   p->setPen(QPen(Qt::lightGray,1));
   int l = int(rect.left());
   l -= (l % 10);
 
   int r = int(rect.right());
   r -= (r % 10);
   if(r < int(rect.right()))
      r += 10;
 
   int t = int(rect.top());
   t -= (t % 10);
 
   int b = int(rect.bottom());
   b -= (b % 10);
   if(b < int(rect.bottom()))
      b += 10;
 
   for( int x = l; x <= r; x+=10)
      for( int y = t; y <= b; y+=10)
         p->drawPoint(x,y);
 
   p->restore();
}

void SchematicScene::drawBackground(QPainter *p, const QRectF& crect)
{
      const QRectF rect = crect.normalized();
   p->save();
   p->setPen(QPen(Qt::lightGray,1));
   int l = int(rect.left());
   l -= (l % 10);

   int r = int(rect.right());
   r -= (r % 10);
   if(r < int(rect.right()))
      r += 10;

   int t = int(rect.top());
   t -= (t % 10);

   int b = int(rect.bottom());
   b -= (b % 10);
   if(b < int(rect.bottom()))
      b += 10;

   for( int x = l; x <= r; x+=10)
      for( int y = t; y <= b; y+=10)
         p->drawPoint(x,y);

   p->restore();
}

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