[cairo] scaled_font lifecycle issue

[Adrian Johnson]

On 10/04/16 09:08, Lawrence D'Oliveiro wrote:
> On Sat, 9 Apr 2016 19:30:01 +0930, Adrian Johnson wrote:
> 
>> Maybe we need a font_face API function to make cairo drop a font from
>> the cache once the application drops all references to the font_face
>> and scaled fonts?
> 
> A more general invalidate-cache-for-specified-font-face function
> would be very useful. It would help with use of multiple-master-type
> font technologies. I hit this situation when implementing my wrapper
> for the Hershey fonts <https://github.com/ldo/hersheypy> for Cairo: to
> use different line widths, I had to load multiple copies of the same
> font to get around Cairo’s caching.

I'm not sure how well this would work for PDF/PS/SVG as these backends
hold on to the font_face of every font used until after all pages have
been emitted before all the fonts are emitted.