Created attachment 38742 [details] [review]
A preliminary patch to cache OS/2.sFamilyClass & OS/2.Panose

As posted in mailing list
http://lists.freedesktop.org/archives/fontconfig/2010-September/003472.html

I propose to store OS/2.sFamilyClass and OS/2.Panose data in fontconfig cache file.

Some office documents (ODF, OOXML), page description languages (PDF, PCL) and
CSS may lookup the font resource by using Panose values.

==================================================================
PDF 
---
PDF Reference 6th edition (for PDF version 1.7)
5.7.2 Font Descriptors for CIDFonts

	see the description for "Style" entry which
	includes 2 bytes from OS/2.sFamilyClass,
	10 bytes from OS/2.Panose.

SVG
---
http://www.w3.org/TR/2003/REC-SVG11-20030114/fonts.html
20.8.3 The `font-face' element

	there are many elements inherited from CSS2,
	including Panose.

ODF
---
http://docs.oasis-open.org/office/v1.1/OS/OpenDocument-v1.1.pdf
14.6.1 CSS2/SVG Font Descriptors

	ODF adopted the elements for the fonts from
	CSS2 and SVG, so even the font is for the text
	(not for embedded scalable graphics), it may
	have Panose value in the svg:panose-1 attribute.
	
OOXML
-----
ISO/IEC 29500-1:2008
17.8.3.13 panose1 (Panose-1 Typeface Classification Number)

	OOXML have several font properties (GDI parameters,
	Panose, and supported unicode range). In 17.8.2 Font
	Substitution, there is a list of properties to be
	used in the font substitution, and panose is described
	as the highest priority.

PCL
---
"PCL 5e Technical Quick Reference Guide"
  http://h20000.www2.hp.com/bc/docs/support/SupportManual/bpl13205/bpl13205.pdf
"PCL5 Comparison Guide"
  http://h20000.www2.hp.com/bc/docs/support/SupportManual/bpl13206/bpl13206.pdf

	PCL5 selects the font by giving Panose parameters
	sequentially and narrowing down the candidates,
	see PCL 5e Technical Quick Reference Guide p 11-15.

	See table 1-1 "PCL5 Feature Support Matrix" in
	page 1-12 PCL5 Comparison Guide, many PCL5
	implementations support the feature to narrow
	down by Panose parameters.

	Also PCL6 (PCL XL) supports the feature by
	giving a string of PCL5 commands to PCLSelectFont
	attribute.
==================================================================
In addition, current fontconfig does not have easy element to
be related with CSS's 5 family classification (serif, sans-
serif, cursive, fantasy). I think getting FamilyClass & Panose
values from fontconfig cache may be helpful, because the
application don't have to open a face, load OS/2 table,
check FamilyClass/Panose values, close a face.

The font selection by the matching of familynames & charsets
leaves a room for an improvement, because severeal documents
formats (and CSS) have these properties in the documents.

--

FreeType2 provides the interface to access them from FT_Face object, so they can
do Panose value checking out of fontconfig library. But if fontconfig can cache these
values, the application programs can reduce the cost to open/check/close font files by
themselves. I attached preliminary patch to cache them.