[Qt-interest] Rendering artefacts when moving QGraphicsItems

[Sean Harmer]

Hi,

On Tuesday 20 Apr 2010 10:41:27 Andre Somers wrote:
> On 24-3-2010 11:50, Andre Somers wrote:
> > Hi,
> > 
> > I noticed what I think is a regression in Qt 4.6.?. At least, I did
> > not notice this effect in Qt 4.5. I am using Qt 4.6.2 on Windows XP.
> > 
> > I have a situation where I have some QGraphicsRectItems that have some
> > child items that are partly outside the bounds of the original item.
> > When I move around the item using drag & drop, I often get rendering
> > artefacts in the sense that the parts of the child items that are
> > outside the parent item are not properly erased. This leaves a 'trail'
> > of leftovers all over the scene if I drag the item around a bit. When
> > the graphics view redraws, the artifacts disapear. Note that the
> > parent item does not leave a trail.
> > 
> > I have reimplemented the boundingRect method to contain the child
> > items ( I thought that this would be automatic ), but that did not
> > help. Could somebody suggest what I might be doing wrong here?
> > 
> > André
> 
> I am still having this issue. I have attached a screenshot showing the
> rendering issues I am running into.
> 
> The first issue is marked with red in the image: the trails of items
> after dragging the item around the view. The second issue is marked in
> purple: te selection rect does not completely coincide with the rect of
> the item itself.
> 
> The item is a subclass of QGraphicsRectItem, which has the little
> colored, partly overlapping rects (also QGraphicsRectItem subclasses)
> and the texts next to these blocks as child items.
> 
> As a try to fix it, I created a QRect that encompasses all the bounding
> rects of all these parts, and used that as the bounding rect. Of course,
> this bounding rect change is announced by calling
> prepareGeometryChange() on the item.
> 
> Does anyone have any tips on what I'm doing wrong here? Again: I did not
> see these issues in Qt 4.5.

Are you able to make a small test case that we can try to reproduce the 
problem with please?

Cheers,

Sean