Re: [ft-devel] Accelerate TrueType interpreter with JIT compiling?

[Werner LEMBERG]

>> [...] TrueType hinting is done by a byte-code interpreter
>> (ttinterp). My question is, is it worth to accelerate this process
>> by JIT?
>
> I highly doubt.

I second that.  What's most important is caching of the processed
glyphs.

> May I ask the purpose of this interpreter?

To move points within a glyph so that it's better hinted.

> Is it only used for font loading, or has other purposes?

It's normally not executed at font loading time, but at glyph loading
time.

> Is the same program runs for all glyphs for the same font (or
> multiple fonts)?

There are three parts: A generic one (in the `fpgm' table, usually
defining functions), a global one (in the `prep' table, to be executed
right after setting a ppem value), and a local one (the real
instructions for every glyph, located in the `glyf' table).

> What is the typical program length (number of bytecode
> instructions)?

It depends.  For extensive manual hinting that covers B/W, grayscale,
and ClearType rendering, it can be more than 500 bytes per glyph.

> Do you have any measurements about the ratio of interpreted runtime
> compared to the total time consumed by freetype?

No, but hinting is quite slow.


    Werner