High DPI Support QPainter::drawText

stvokr

Hi Guys,

I have a problem with HighDPI-Support and drawing text into an image with a painter.
HighDPI-Support is activated (before the QApplication is started) via

QApplication::setAttribute( Qt::AA_EnableHighDpiScaling );
QApplication::setAttribute( Qt::AA_UseHighDpiPixmaps );

The image and the text is drawn as follows:

QPixmap image = source->scaledToWidth( newWidth, Qt::SmoothTransformation );
...

QPainter painter( &image );
painter.setRenderHint( QPainter::TextAntialiasing );
painter.setRenderHint( QPainter::Antialiasing );
painter.drawText( rect, Qt::AlignCenter, str );

ui.label_image->setPixmap( image );

The result is an aliased text in the image (this is on a 4K monitor).

If I disable high DPI support, the text in the image is better, especially antialiazed (this is on a FullHD Monitor).

As I write this post, I noticed that not only the text, but also the image itself (HighDPI version) is aliased.
Does anybody know why?

regards
Oliver

SGaist

Hi,

Sorry I don't have a direct answer for that. In any case what version of Qt are you using ? There's been quite some work on the HighDPI side in the latest releases which may behave better.

stvokr

I'm using Qt 5.12.5.

SGaist

You should try with Qt 5.14.1 to see if it as improved.

stvokr

Qt 5.14.1 has the same problem.

SGaist

Did you check the bug report system ?