Re: [PATCH] Faster text rendering by optimizing font glyph lookup

[Felix Zielcke]

Am Donnerstag, den 11.06.2009, 23:31 +0200 schrieb Vladimir 'phcoder'
Serbinenko:
> On Thu, Jun 11, 2009 at 12:28 PM, Felix Zielcke<address@hidden> wrote:
> > Am Montag, den 09.02.2009, 08:24 -0800 schrieb Colin D Bennett:
> >> On Mon, 9 Feb 2009 15:11:16 +0100
> >> Robert Millan <address@hidden> wrote:
> >>
> >> > On Sun, Feb 08, 2009 at 01:49:53PM -0800, Colin D Bennett wrote:
> >> > > This patch greatly—*tremendously*, even, if higher-numbered Unicode
> >> > > characters are used—speeds up retrieving a glyph for a particular
> >> > > Unicode character.  This makes text rendering in general much faster.
> >> > >
> >> > > My text benchmark shows the new text rendering speed is somewhere from
> >> > > 2.6x to 31x of the previous speed.  Basically, PFF2 font files are now
> >> > > required to have the character index ordered in ascending order of code
> >> > > point.
> >> > >
> >> > > Fonts created by 'grub-mkfont' already satisfy this requirement.  Fonts
> >> > > created by my old Java 'fonttool' do not, and cannot be used any 
> >> > > longer.
> >> > >
> >> > > The font loader verifies that fonts fulfill the character ordering
> >> > > requirement, refusing to load invalid fonts, but the primary change is
> >> > > in the 'find_glyph()' function, which now uses a binary search rather
> >> > > than a linear search to find the glyph.
> >> >
> >> > Very nice!
> >> >
> >> > With this patch, how does retrieving glyphs from the complete unicode 
> >> > font
> >> > compare to retrieving glyphs (without the patch) from the ascii ascii 
> >> > one?
> >>
> >> Here is the result of my benchmark with two kinds of text:
> >> (1) 104 characters of ASCII English text, and
> >> (2) 104 Unicode characters randomly selected from the characters in
> >>     unifont, uniformly distributed over all 61050 characters in the
> >>     font.
> >>
> >> Also, I ran the tests with both the 'ascii.pf2' and 'unicode.pf2' font
> >> files generated by GRUB's Makefile.  Here are the results:
> >>
> >> ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
> >> 9 February 2009 videotest bench, text rendering
> >> benchmark 640x480 resolution
> >>                               ASCII Text  Unicode Text
> >> Algorithm       Unifont used   (Chars/s)   (Chars/s)
> >> --------------- ------------- ----------  ------------
> >> Linear search   ASCII Font      255113       12098 [1]
> >> Linear search   Unicode Font    250874       23068 [2]
> >> Binary search   ASCII Font      255746       96231 [1]
> >> Binary search   Unicode Font    255113      194741 [2]
> >>
> >> [1] Note that using the ASCII font for Unicode text results in a
> >>     performance hit because the grub_font_draw_string() function will
> >>     use font fallback to search for the missing glyphs in another
> >>     font.  I had other fonts loaded while running the benchmark, so
> >>     GRUB had to scan them for the missing characters.
> >>
> >> [2] These numbers, for full Unicode text with the full unifont, show
> >>     the improvement in worst-case performance when using the binary
> >>     search versus linear search.
> >> ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
> >>
> >> Note that most of the time is now spent actually rendering the bitmaps
> >> on screen (instead of retrieving glyphs from the font), which actually
> >> takes longer for the Unicode text because many of the glyphs are wider
> >> than the English ASCII characters.
> >>
> >> (BTW, is there any way to run GRUB in a profiler?  I'd like to know
> >> where the graphics performance bottlenecks are.)
> >>
> >> > Can we make unicode font the default now?
> >>
> >> I think so.  Using the full Unicode font does not seem to have a
> >> significant effect on rendering speed now.  I will commit the patch if
> >> it looks OK to you.
> >>
> >
> > Now that Vladimir finally commited this, should we make it now the
> > default or not?
> I think we can make unicode fonts default now. Don't get too
> overexcited though: we still lack ligatures. I don't know if composing
> accents work and no bidi.But this subset is already enough to support
> all European languages, Chinese, Korean and Japanese as long
> characters are precomposed

So if there still won't come up objections against this, then I'll do
the change, then at least an Ubuntu bug report can be closed.

-- 
Felix Zielcke