Qt4-preview-feedback Archive, January 2008
boundingRegion() / granularity / itemCache
Message 1 in thread
Hi all,
I just installed today's 4.4 snapshot (20080110) to test the feature Andreas mentioned in his blog entry: http://labs.trolltech.com/blogs/2008/01/08/accurate-update-regions-for-thin-qgraphicsitems/
Looking at the ported canvas source I found the granularity for the edge to be set to 0.05.
While I notice a small performance increase, it is yet far from optimal, I would say.
I tried to further increase the performance by enabling the itemCache (http://labs.trolltech.com/blogs/2007/09/05/thoughts-about-graphics-performance/)
setCacheMode(QGraphicsItem::ItemCoordinateCache);
but that results in QPainter spitting out bunches of errors as soon as I create a mesh:
brws7001-adapt$ QPainter::begin: Cannot paint on a null pixmap
QPainter::renderHints: Painter must be active to set rendering hints
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setWorldTransform: Painter not active
QPainter::setWorldTransform: Painter not active
QPainter::end: Painter not active, aborted
QPainterPath::moveTo: Adding point where x or y is NaN, results are undefined
QPainterPath::lineTo: Adding point where x or y is NaN, results are undefined
[some hunderd msg deleted]
QPainter::begin: Cannot paint on a null pixmap
QPainter::renderHints: Painter must be active to set rendering hints
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setWorldTransform: Painter not active
QPainter::setWorldTransform: Painter not active
QPainter::end: Painter not active, aborted
QPainter::begin: Cannot paint on a null pixmap
QPainter::renderHints: Painter must be active to set rendering hints
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setWorldTransform: Painter not active
QPainter::setWorldTransform: Painter not active
QPainter::end: Painter not active, aborted
Any idea?
I am under SuSE Linux 10.2.
\Ralf
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Message 2 in thread
Hi, Ralf.
Ralf Neubersch wrote:
>
> I just installed today's 4.4 snapshot (20080110) to test the feature
> Andreas mentioned in his blog entry:
> http://labs.trolltech....update-regions-for-thin-qgraphicsitems/
> Looking at the ported canvas source I found the granularity for the edge
> to be set to 0.05.
> While I notice a small performance increase, it is yet far from optimal, I
> would say.
The purpose of the granular bounding region is to minimize unnecessary
updates; it doesn't prevent items that are crossed from being redrawn.
> I tried to further increase the performance by enabling the itemCache
(http://labs.trolltech.com/blogs/2007/09/05/thoughts-about-graphics-performance/)
> setCacheMode(QGraphicsItem::ItemCoordinateCache);
> but that results in QPainter spitting out bunches of errors as soon as I
> create a mesh:
The painter warnings are a bug, we're investigating this now.
--
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