[QQuickPaintedItem] Problem with drawing text and lines

maksim1979

Hello,

I have a subclass of QQuickPaintedItem and paint method is quite simple
@
//setRenderTarget(QQuickPaintedItem::FramebufferObject );
painter->setRenderHint(QPainter::TextAntialiasing);
painter->setRenderHint(QPainter::Antialiasing);
QPen pen(Qt::black, 1, Qt::SolidLine, Qt::FlatCap, Qt::MiterJoin);

painter->setPen(pen);
painter->setBrush(Qt::NoBrush);

painter->drawLine(100, 10, 100, 200);
painter->drawLine(10, 50, 107, 50);

painter->drawText(50, 40, "some text");

@

The problem here is that with FramebufferObject render target the text is ok but lines width is not 1. If I change render target to Image(default), the text looks ugly but the lines are ok. Any thoughts how to fix that?

!http://i.imgur.com/6iJ4VDy.png()!
!http://i.imgur.com/AUETJKr.png()!

Thanks a lot,
Maxim

maksim1979

It's possible to use Imgae for drawing, something like that
@
void paint(QPainter *painter)
{
QImage image(width(), height(), Image::Format_ARGB32_Premultiplied);
QPainter imagePainter(&image);

draw(imagePainter);

painter->drawImage(image);

}
@

But I'm not sure about performance with this approach

mnaydenov

To get the lines to draw right you must use float coordinates and snap them to pixel center.

Instead of

@painter->drawLine(100, 10, 100, 200);@

do

@painter->drawLine(100+0.5, 10+0.5, 100+0.5, 200+0.5);@

If it still looks blurry, it is because your item coords are not snapped to pixel bounds. This is, make sure you round your x and y pos (of the item itself) to an int.

DISCLAIMER all this comes from a ton of exp with GraphicsView framework, but it should apply to qquick as well, because it is how (Antialiased) drawing works - you must pixel align.

maksim1979

Yep, thanks a lot. I've tried float coordinates but it didn't help. But I found that if I disable antialiasing (remove this line painter->setRenderHint(QPainter::Antialiasing); ), the line looks ok.