Re: [Devel] default stem width and height for autohinting

[Vadim Plessky]

On Friday 02 May 2003 12:42, Werner LEMBERG wrote:
|  The function `ah_hinter_compute_widths' relies on the existence of
|  glyph `o' in the font.  What about searching for alternative glyphs
|  depending on the font?  Especially in non-latin fonts, using `o' is a

Does autohinter use 'o' to calculate stem width and height (hstem, vstem) ?
This would be really surprise me (and explain some rendering artefacts in 
current FT).
I think 'H' can be used for Vstem and Hstem values, and 'F'  - for HStem.
Widths of both horizontal and vertical stems in 'O' and ('C', 'o', 'c') are 
higher than for 'H' (about 96 for H and 100 to 106 for O as VStem value in 
PostScript coordinates /1000 units/ for typical Sans font) 

On the other hand, I think autohinter should scan all Latin, Cyrillic, Greek 
Unicode ranges, and take weighted values for HStem/Vstem using those ranges.
As far as Iknow, some font formats support different Hstem/Vstem values for 
different Unicode ranges 9in particular - fro CJK ranges).
So indeed, Hstem/Vstem for CJK fonts should be calculated separatly .

|  bad idea, since there a lot of fonts (especially CJK ones) which have
|  extremely ugly shapes for ASCII since it is never used.  Even worse,
|  the typographic properties can differ enormously between such ASCII
|  glyphs and the real glyphs the font is used for.  The same problem
|  exists for computing blue zones in `ah_hinter_compute_blues'.
|
|  Perhaps it makes sense to derive different global autohinting
|  properties depending on the character range.  For example, a
|  hyphothetical Near East font contains glyphs for Hebrew, Arabic, and
|  the latin script.  If a Hebrew glyph has to be rendered, global
|  autohinting properties derived from Hebrew glyphs only should be used.
|  The same holds for Arabic and latin glyphs.
|
|  It shouldn't be too difficult to implement that.  The `blue_chars' has
|  to become two-dimensional in some way, and we have to define leading
|  characters for the various Unicode ranges to derive default stem width
|  and height values.  For CJK, to name an example, a typical glyph could
|  be the character for `ten': `十'.
|
|  Has anybody already done some tests whether this really improves
|  autohinting results?
|
|      Werner
|
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-- 

Best Regards,

Vadim Plessky
SVG Icons * BlueSphere Icons 0.3.0 released
http://svgicons.sourceforge.net