[Fontconfig] editing FcConfig in code

[Idriss Fekir]

On 4/12/23 08:45, Akira TAGOH wrote:
> First of all, Please note that "Regular" style is default style
> though, most applications request *Regular weight* instead of style
> name. So the correct command to represent a request is `fc-match
> "Amber Whiskey:weight=regular".
> Based on that, let's see what happened.
> 
> AmberWhiskey-Aged.otf has two family names. one is "Amber Whiskey" and
> one is "Amber Whiskey Aged". And, weight is set to 80 which is the
> same as FC_WEIGHT_REGULAR. So the behavior itself isn't wrong.
> 
> Second, I don't recommend using the above config because that will
> break non-Regular selection. I didn't test but this may works instead:
> 
> <match>
>    <test name="family">
>      <string>Amber Whiskey</string>
>    </test>
>    <test name="weight">
>      <const>regular</const>
>    </test>
>    <test qual="all" name="style" compare="eq">
>      <string></string>
>    </test>
>    <edit name="style">
>      <string>Regular</string>
>    </edit>
> </match>
> 
> This will add Regular to style property only when weight is set to
> "regular" and no styles is set. you can still pick up the aged variant
> with "Amber Whiskey:style=Aged".
> 
> If you don't want to see the aged variant as a part of "Amber
> Whiskey", things would be much simpler. you may have another
> workaround like this:
> 
> <match target="scan">
>    <test name="family">
>      <string>Amber Whiskey</string>
>    </test>
>    <test name="family">
>      <string>Amber Whiskey Aged</string>
>    </test>
>    <edit name="family" mode="delete" />
> </match>
> 
> This will modify the fontconfig cache. AmberWhiskey-Aged.otf is then
> represented as "Amber Whiskey Aged" only.
> 
> For your original question, if there are any reasons you can't put
> something into a config file, you can use
> FcConfigParseAndLoadFromMemory() function as said in other mail.
> otherwise you can create your own config for a workaround and put it
> into $HOME/.config/fontconfig or something like that.
> 
> Hope that helps,
> 
> On Wed, Apr 12, 2023 at 9:12 AM Idriss Fekir <mcsm224 at gmail.com> wrote:
>>
>> Hi,
>>
>> Some fonts aren't matched by fontconfig correctly e.g: the Amber Whiskey
>> family has 4 faces Regular, Aged, Full Color, Shadow.
>> `fc-match "Amber Whiskey"` outputs "Aged" instead of "Regular", And
>> since Pango relies on fontconfig for that, it also exhibits the same
>> behavior (e.g: Inkscape an gimp, both rely on pango, would pick the
>> "Aged" variant). This could be worked around with a rule:
>>
>> ```
>> <match target="pattern">
>>       <test name="family">
>>           <string>Amber Whiskey</string>
>>       </test>
>>       <edit name="style">
>>           <string>Regular</string>
>>       </edit>
>> </match>
>> ```
>>
>> My question is how can i do that but in code (in C), that is
>> how can i check what fc-match would output, then if the output is wrong
>> add a rule like the following to the FcConfig?
>>
>> I'm open to suggestions if there are better ways.
>>
>> I did read the docs but i couldn't figure out how.
>>
>> The man page for FcFontMatch says that it should only be called after
>> FcConfigSubstitute and FcDefaultSubstitute have been called for
>> the pattern, i don't understand what that means exactly.
>>
>> Thanks a lot.
> 
> 
> 
Thanks for your replies Jean and Akira.

Akira, your first solution worked, but i don't understand what you meant 
that my config breaks non-regular selection, all other variants are 
matched correctly.

Some faces of Iosevka (e.g Iosevka Fixed Extrabold Extended Oblique is 
matched as NotoSans Italic) also have this problem but fc-match returns 
the fallback font, so I'm not sure how to fix that .

Is there a way to match fonts by their PostScript name?

My goal is, at application startup to check for fonts that aren't 
matched properly, then remap then load the config, is there a general 
solution?

Thanks
-- 
Idriss