QGraphicsView: per-item antialiasing specification?

[mattc]

Hello,
is it possibile to specify a per-item antialias rendering in a QGraphicsView? As far as I understand QGraphicsView::setRenderHint affects all of the items, but in my application some items would look nicer without aliasing.

Thanks

[aamer4yu]

You can use / not use aliasing in the QGraphicsItem::paint itself,, cant you ?

[Lykurg]

If you don't want to do all the drawings yourself, subclass you needed item and adjust the flags:

void MyGraphicsItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
  painter->setRenderHint(painter->renderHint() /*...*/);
  YourBaseClass::paint(painter, option, widget);
}

void MyGraphicsItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
  painter->setRenderHint(painter->renderHint() /*...*/);
  YourBaseClass::paint(painter, option, widget);
}

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[mattc]

Hello aamer4yu,
somehow such a simple solution didn't cross my mind! Here is the working code:

void MyGraphicItem::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget)
{
    painter->setRenderHint(QPainter::Antialiasing);
    QGraphicsEllipseItem::paint(painter, option, widget);
    painter->setRenderHint(QPainter::Antialiasing, false);
}

void MyGraphicItem::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget)
{
    painter->setRenderHint(QPainter::Antialiasing);
    QGraphicsEllipseItem::paint(painter, option, widget);
    painter->setRenderHint(QPainter::Antialiasing, false);
}

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Thank you very much.

[mattc]

thanks Lykurg,
I've seen your reply after posting. I removed the line restoring the painter state, and changed the first line to preserve existing render hints.

void MyGraphicItem::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget)
{
    painter->setRenderHints(painter->renderHints() | QPainter::Antialiasing);
    QGraphicsEllipseItem::paint(painter, option, widget);
}

void MyGraphicItem::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget)
{
    painter->setRenderHints(painter->renderHints() | QPainter::Antialiasing);
    QGraphicsEllipseItem::paint(painter, option, widget);
}

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Btw, browsing the docs I found some inconsistency about the render hints functions. From QPainter:

The renderHints() function returns a flag that specifies the rendering hints that are set for this painter. Use the setRenderHint() function to set or clear the currently set RenderHints

so, what is setRenderHint*s*() supposed to do? Also, no "renderHint()" in QPainter.

[Lykurg]

so, what is setRenderHint*s*() supposed to do? Also, no "renderHint()" in QPainter.

Yeah, I was mixing up some things. It's:

QPainter::setRenderHint ( RenderHint hint, bool on = true );

QPainter::setRenderHint ( RenderHint hint, bool on = true );

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or

QPainter::setRenderHints ( RenderHints hints, bool on = true );

QPainter::setRenderHints ( RenderHints hints, bool on = true );

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with hints g.e. "QPainter::Antialiasing|QPainter::TextAntialiasing ".