[Development] High-dpi Qt best practices

[Olivier Goffart]

What is wrong with this alternative:

All the API stays always in pixel  (QIcon, QWidget::geometry, ...)

QCoreApplication::setAttribute(Qt::AA_MacHighDPI)
(should it maybe be even be set by default?)

If that is set, everything is in pixel, but the default font size is twice as 
big, the mac style returns pixelmetrics ans sizes that are twice as big, and 
all the widgets are then automatically twice as big

In general, that's the way to do it.  Having hardcoded pixel value has always 
been a bad practice with Qt.
Application that did it will possibly look bad on high-res display and will 
need to be fixed.  But I think they will need the same amount of fixes with 
the other appreach because sometimes they really mean pixel, sometimes they 
mean point.


The only thing is about QPen. should we draw lines twice as large?  that is 
bascically what QPen::isCosmetic is for.

-- 
Olivier

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