Why doesn't QT cache the bounding rect for QPainterPaths?

I had a HUGE performance issue and wasn't sure what was causing it, I eventually narrowed it down to a QPainterPath boundingRect() issue.

I had a QGraphicsItem subclasses line which drew its line with a QPainterPath. So in the subclassed class's boundingRect() function I called mypath.boundingRect(). Turns out that thats a really slow call!.

Saving the results to a QRectF had a drastic impact on performance.

Why doesn't it internally cache the bounding rect if its computation is complex?

It seems that Qt 4.4.0 does cache it:

Code:

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QRectF QPainterPath::boundingRect() const
{
    if (!d_ptr)
        return QRectF();
    QPainterPathData *d = d_func();
 
    if (d->dirtyBounds)
        computeBoundingRect();
    return d->bounds;
}

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Which Qt version do you use?

Hmm then I must be doing something that is causing it to think it needs to recaculate all the time. :(

Is there a good way to identify this kind of a bug?

Quote:

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Originally Posted by mooreaa

Hmm then I must be doing something that is causing it to think it needs to recaculate all the time.

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Maybe you create a new path every time?