Efficient Scaling and Rotating of QGraphicsView

[forrestfsu]

No, I don't use OpenGL to draw the background. I do use painter and here is the code:

void Override::drawBackground(QPainter *painter, const QRectF &rect)
{
 painter->save();
 painter->setBrush(Qt::black);
 painter->drawRect(rect);
 painter->drawPixmap(0,0, theForm->getBackground()); // getBackground() returns a pixmap
 painter->restore();
} 
 
QPixmap theForm::getBackground()
{
 return backgroundImage; // This is an image stored in a classes QPixmap variable.
}

void Override::drawBackground(QPainter *painter, const QRectF &rect)
{
 painter->save();
 painter->setBrush(Qt::black);
 painter->drawRect(rect);
 painter->drawPixmap(0,0, theForm->getBackground()); // getBackground() returns a pixmap
 painter->restore();
} 

QPixmap theForm::getBackground()
{
 return backgroundImage; // This is an image stored in a classes QPixmap variable.
}

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[wysota]

I'm not sure, but it is possible that you need to draw the background using OpenGL code. Unfortunately "chips" doesn't draw a background, so we can't check in the example...

The pixmap you're using is very big, so obviously transforming it is very expensive. I understand that the background is getting rotated and scaled when items get scaled and rotated, correct?

[forrestfsu]

I'm not quite sure I understand what you mean by "the background is getting rotated and scaled when items get scaled and rotated." So I'll try and explain:

This specific graphicsView has a scene which it shares with 5 other graphicsView's. The only difference with this graphicsView is that I use drawBackground() to give it a unique background Pixmap (in this case a very large pixmap). I have zoom and rotate buttons on the widget which call the ScaleView() function for this graphicsView. ScaleView() scales and rotates all the contents within this graphicsView (the scene contents and the large background Pixmap).

Hope this clears it up.

[forrestfsu]

An additional note. Once the user has scaled the image to a different ratio then the original, even using the scroll bars for the graphicsView lag moving the content of the graphicsView.

[forrestfsu]

I just fixed the problem (still a few minor bugs to go through). Instead of returning an entire Pixmap, I needed only return the area of the Pixmap that I needed to display using the QPixmap's copy function. After I have all the code in place I will paste it for review.

Thanks Wysota for all your help on this issue.