[Qt-interest] QGraphicsView, invalidateScene and ForegroundLayer

[Christian Gagneraud]

Hi there,

First of all: I'm using NokiaQtSDK-1.0, on fedora-12, 32 bits.

According to the documentation QGraphicsView::invalidateScene() can be 
used to reschedule a redraw of layers. And especially it says "You can 
call this function to notify QGraphicsView of changes to the 
background or the foreground of the scene", I'm agree that further up 
the doc says "Note that QGraphicsView currently supports background 
caching only [...]", and that what has confused me at first.

I tried to use this function to reschedule a redraw of the foreground 
from QGraphicsView::mouseEvent(), but it didn't work, i then looked at 
the source code, and realized that the code deals only with the 
background layer (ie, it does absolutely nothing if layers doesn't 
contain QGraphicsScene::BackgroundLayer).

So my question is: Is it me that misunterstood the documentation? Is 
it QGraphicsView::invalidateScene() that doesn't do what's advertised 
or is it the documentation which is wrong or unclear?

I ended up calling QGraphicsScene::invalidateScene() from 
QGraphicsScene::mouseEvent(), but I'm not really happy, because all my 
logic and the revelant informations are managed from inside the view, 
not the scene.
What I'm trying to do, is draw a grid on the background, and draw 
rules and a snapped-to-grid mouse pointer on the foreground.

Regards,
Chris

-- 
Christian Gagneraud,
Electronics and software engineer

TechWorks Marine Ltd
4a, Park Lane
Dun Laoghaire, Co Dublin
Ireland

Tel: + 353 1 2365990
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