GraphicsView update background

[maverick_pol]

Hi,

I have already enabled updates for the graphicsView, set cacheBackground as the mode for updating the gview. I need to change the background color. WHen I set the colour and invoke update/repaint for the view or viewport nothing happens. When I invoke "fitInView(..sceneRect)" the background is repainted.
How to update the background using update/repaint/etc ?
My view settings:

...
m_view->setCacheMode(QGraphicsView::CacheBackground);
 m_view->setOptimizationFlag(QGraphicsView::DontClipPainter);
m_view->setOptimizationFlag(QGraphicsView::DontSavePainterState);
m_view->setViewportUpdateMode(QGraphicsView::FullViewportUpdate);
m_view->setRenderHints( QPainter::HighQualityAntialiasing);
m_view->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
m_view->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
....

...
m_view->setCacheMode(QGraphicsView::CacheBackground);
 m_view->setOptimizationFlag(QGraphicsView::DontClipPainter);
m_view->setOptimizationFlag(QGraphicsView::DontSavePainterState);
m_view->setViewportUpdateMode(QGraphicsView::FullViewportUpdate);
m_view->setRenderHints( QPainter::HighQualityAntialiasing);
m_view->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
m_view->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
....

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While initializing the view I can set view->setBackgroundColor(Qt::blue),etc. And it works fine. But how to update the backgroundcolor later?

Thanks.

[wysota]

How about using QGraphicsScene::setBackgroundBrush()?

[maverick_pol]

setBackgroundBrush overides scene's background. I have a custom background in the scene and do not want to change this. Scene rect is smaller than the view size, and to hide that I need to set the same colour for the view and for the scene.

[wysota]

In that case try changing the QPalette::Base component of the view's palette.

[maverick_pol]

This do not work:

QPalette	palette;
palette.setBrush(QPalette::Base,m_colorMap.value("NODTA"));//NODTA-> is my color index
m_view->setPalette(palette);
m_view->repaint(true);

QPalette	palette;
palette.setBrush(QPalette::Base,m_colorMap.value("NODTA"));//NODTA-> is my color index
m_view->setPalette(palette);
m_view->repaint(true);

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Still using fitInview -> changes the background. Maybe you have and idea what is invoked in the fitInView? (I know the view is transformed /scaled)

Kacper

[maverick_pol]

Ok,

I might have found the problem. While changing the background, the view(if the cachBackground is enabled) repainted the background from the cache. When I turned off the cachBackground the repainting works. yet, I can't turn off the background cache, because repainting works 10x slower.

I can reset the cache, but it works slower. Howto update the view background without clearing the cache?(when the cache is enabled) ?

Kacper

[wysota]

Maybe you should manualy call update()?

[maverick_pol]

I tried that already. Nothing happens.

[wysota]

Don't you think that every update causes the background cache to be regenerated? If so, you can turn off the cache, redraw the background and then turn the cache back on.

[pherthyl]

Well if you are changing something in the background then naturally you need to reset the cache. As you seem to have discovered, QGraphicsView::resetCachedContent () is the key to that.
Of course the following repaint will be slower because it needs to regenerate the cache. You can't get away from that.