Easier way to disable Harfbuzz?

[systemed]

For cycle.travel I'm using a font which doesn't have ligatures.

Rendering this with Harfbuzz results in the letter-pairs going AWOL entirely, so "Cardiff" becomes "Cardi", "Bakersfield" becomes "Bakerseld" etc. (This may be a bug in the font, of course.)

As per #2875, export HB_SHAPER_LIST=fallback should disable Harfbuzz, but I've not found any way to get this through renderd into Mapnik. (This may be a bug in renderd, of course.)

Eventually I fixed it in the grand hackish tradition by replacing the call to harfbuzz_shaper in src/text/text_layout.cpp with one to icu_shaper. But it might be good to have this as an option in TextSymbolizer rather than an environment variable.

[talaj]

You don't have to switch to another text shaper to workaround problem with ligatures. You can just turn ligatures off:

<TextSymbolizer face-name="DejaVu Sans Book" font-feature-settings="liga 0">
    "Text without ligatures"
</TextSymbolizer>

Also good to know is that Mapnik automatically turns off ligatures when character-spacing is greater than zero. See #2416.

Btw, great project, @systemed!

[systemed]

That works great - thanks for the tip! I've now moved to Harfbuzz as I was getting some other (Czech-language!) font rendering issues which it solves.