https://bugs.documentfoundation.org/show_bug.cgi?id=112805
--- Comment #8 from LibreTraining <libretraining.tutori...@gmail.com> ---
(In reply to Volga from comment #7)
> So LibreOffice should add a function to handle "size" feature via font size
> option.
No. When the "size" feature is enabled the font substitution should happen
automatically based on the font size selected.
Each font has a range of sizes for which it should be used.
Coelacanth font family for example:
Coelacanth has Optical Size features
Pearl
Design Size: 5.0
Range: 4.0 – 5.5
Subcapt
Design Size: 6.0
Range: 5.6 – 6.9
Caption
Design Size: 9.0
Range: 7.0 – 10.9
Regular
Design Size: 14.0
Range: 11.0 – 17.2
Subhd
Design Size: 24.0
Range: 17.3 – 32.9
Display
Design Size: 60.0
Range: 33.0 – 72.0
The actual font file used depends on the size the user selects.
If the user select 12pts as the size, the Regular font file will be used.
If the user select 18pts as the size, the Subhd font file will be used.
If the user select 48pts as the size, the Display font file will be used.
Apparently Harfbuzz does have this feature, but I did not see it anywhere in
Pango the text rendering engine docs.
======
(In reply to RGB from comment #0)
> ...
> This feature is governed by the "size" OpenType table. Systems like XeTeX
> automatically pick the right font file to be used on the appropriate size,
> but it seems that LibreOffice gets confused by that table: not only it do
> not switch between variants, it's not even possible to select which variant
> is being used as you can see on the attached screenshot. In fact Coelacanth
> consist of 37 font files tied together by the "size" OT feature, but LibO
> only offers a small and rather arbitrary selection.
>
This inability to properly select the different font weights in a font family
is a known problem.
That is why there is a "small and rather arbitrary selection" of the fonts
installed.
See:
Bug 69254 - Correct handling of font families (weight, style, stretches) on Mac
https://bugs.documentfoundation.org/show_bug.cgi?id=69254
Bug 98596 - Correct handling of font families (weight, style, stretches) on
Linux
https://bugs.documentfoundation.org/show_bug.cgi?id=98596
Because of that problem it is doubtful this feature can be implemented.
That problem would have to be solved first.
For example in Coelacanth there are multiple weights for each optical size.
Which weight would be used would be random/broken like any other font family.
The same problem with most SemiBold fonts, even the ones included with
LibreOffice.
Until LibreOffice can fix the font families problems, this feature has no
chance.
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