Re: [ft] freetype and multithread

[david turner]

Hello,

just use a distinct FT_Library object per thread, and everything should work
ok. We don't support finer parallelism for very good reasons, the first 
of them
being to keep the code simple.

Also, I don't really understand why the font loading/rasterization 
performance is
your bottleneck; the performance of your cache should be where most 
optimizations
should happen.

regards,

- David Turner
- The FreeType Project  (www.freetype.org)


Erich Martin a écrit :
> since I may soon need to use truetype fonts, I am looking to replace my
> current Type1/CID-only font lib with freetype. I quickly hacked some glue
> code around freetype to switch from the current lib and it worked fine.
>
> I had however a problem when I tried to optimize the interface with my
> application. This app is multithreaded and run on multi-processor machines.
> In order to run at full speed, several threads needs to be able to
> simultaneously render the same glyph from the same font at different sizes.
> The font is loaded once and put in a cache (the glyphs too, of course). The
> font is basically read-only data. Each thread then have its own "working
> memory" & size info it pass to the font library API used to render a glyph.
> I need to do this because :
> *there can be a lot of threads and having fonts loaded multiple times will
> require too much memory and decrease performances instead of using a common
> read/write-locked huge cache
> *rendering glyphs and copying them is basically the only work done by the
> threads (they are writing a printing dataflow to bitmaps). Having a mutex on
> the library or fonts will waste lot of cpu time, even if the cache have a
> good hit/miss ratio (specially with eastern fonts where the ratio is always
> lower)
>
> How can I do that with Freetype ? The size info and the glyph slot seems to
> be tied to the loaded font and the rendering pipeline doesn't look fully
> reentrant. What is exactly the actual reentrance degree of freetype ? :
> *library-level (simultaneous rendering from different fonts)
> *font-level (simultaneous rendering of different glyphs from same font)
> *glyph-level (simultaneous rendering of same glyph from same font)
> And, if not reentrant, is there a lot of work to make it so, down to
> glyph-level ?
>
>
>
>
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>
>   

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