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

[Felix Zielcke]

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?
-- 
Felix Zielcke