[Development] Why on Linux using FreeType engine fonts are rendered in 72 dpi instead of Screen DPI?

[Allan Sandfeld Jensen]

On Mittwoch, 17. Oktober 2018 22:11:38 CEST Tomasz Olszak wrote:
> Ok,
> It's a lot more clear. Thank you for explanation!
> 
> I used default font with pixel size 100 and according to FontMetrics:
> 1. family: "Sans Serif"
> 2. pointSize: 75
> 3. pixelSize: 100
> 4. ascent 93
> 5. descent: 24
> 6. height: 117
> 7. leading -1
> 
> So how ascent, descent, leading is related to 100. How can I calculate
> font.pixelSiize knowing that capital letter height is 100. By trial
> and errors the font with pixel size = 137 and ascent = 129 have
> capital letter(without accent) of 100 pixel height.
> Is it a way to determin font.pixelSize if we want the non accent
> capilat letter to be e.g 100px? Or should I just iterate over pixel
> sizes and calculate using fontMetrics and tightBoundingRect for
> capitalized letter without accent?
> 
You should read the capHeight of the font. I think QFontMetrics can give you 
that (https://doc.qt.io/qt-5/qfontmetrics.html#capHeight), though I am not 
sure if there are QML bindings for that. In any case capital latin letters are 
generally all the same height, so you could probably just measure the height 
of H or M.