[Qt-interest] Transparent QGraphicsProxyWidget

[Aron Bierbaum]

I believe that I have tracked it down to a change [1] to the painter
composition mode when rendering a subpixmap into the entire cached
pixmap. I have been unable to find the correct bug to read more about
what this commit fixed, but it seems that it might have broken our use
case. I would think that since we are re-drawing a section of a cached
item we would not have a need for blending. Can anyone provide more
information about why this is being done, and how I could potentially
work around the issue?

-Aron

[1] http://qt.gitorious.org/+qt-s60-developers/qt/qt-s60/commit/39392326c8c843a6f46b864c6595a5241a47af10?diffmode=sidebyside

On Sun, Feb 21, 2010 at 10:31 AM, Aron Bierbaum <aronbierbaum at gmail.com> wrote:
> We have an application that uses stylesheets to set the background
> color of widgets to be transparent before adding to
> QGraphicsProxyWidgets and a QGraphicsScene. This allows us to have
> semi-transparent windows moving around the canvas so that we can see
> what is behind them. Recently we have upgraded from 4.6.0 to 4.6.2 and
> we now see some rendering artifacts when caching the graphics items.
> It appears that the pixmap that we are caching into doesn't get
> completely cleared before re-drawing. Since the background is
> semi-transparent this results in rendering artifacts. Does anyone know
> how to account for this in 4.6.2 so that we get the same behavior as
> we saw with 4.6.0? I have attached a simple example showing the issues
> we are seeing.
>
> Thank you,
> Aron
>