NAME

       Font::TTF::OS_2 - the OS/2 table in a TTF font

DESCRIPTION

       The OS/2 table has two versions and forms, one an extension of the other. This module
       supports both forms and the switching between them.

INSTANCE VARIABLES

       No other variables than those in table and those in the standard:

           Version
           xAvgCharWidth
           usWeightClass
           usWidthClass
           fsType
           ySubscriptXSize
           ySubScriptYSize
           ySubscriptXOffset
           ySubscriptYOffset
           ySuperscriptXSize
           ySuperscriptYSize
           ySuperscriptXOffset
           ySuperscriptYOffset
           yStrikeoutSize
           yStrikeoutPosition
           sFamilyClass
           bFamilyType
           bSerifStyle
           bWeight
           bProportion
           bContrast
           bStrokeVariation
           bArmStyle
           bLetterform
           bMidline
           bXheight
           ulUnicodeRange1
           ulUnicodeRange2
           ulUnicodeRange3
           ulUnicodeRange4
           achVendID
           fsSelection
           usFirstCharIndex
           usLastCharIndex
           sTypoAscender
           sTypoDescender
           sTypoLineGap
           usWinAscent
           usWinDescent
           ulCodePageRange1
           ulCodePageRange2
           xHeight
           CapHeight
           defaultChar
           breakChar
           maxLookups

       Notice that versions 0, 1, 2 & 3 of the table are supported. Notice also that the Panose
       variable has been broken down into its elements.

METHODS

   $t->read
       Reads in the various values from disk (see details of OS/2 table)

   $t->out($fh)
       Writes the table to a file either from memory or by copying.

   $t->XML_element($context, $depth, $key, $value)
       Tidies up the hex values to output them in hex

   $t->XML_end($context, $tag, %attrs)
       Now handle them on the way back in

   $t->minsize()
       Returns the minimum size this table can be. If it is smaller than this, then the table
       must be bad and should be deleted or whatever.

   $t->update
       Updates the OS/2 table by getting information from other sources:

       Updates the "firstChar" and "lastChar" values based on the MS table in the cmap.

       Updates the sTypoAscender, sTypoDescender & sTypoLineGap to be the same values as
       Ascender, Descender and Linegap from the hhea table (assuming it is dirty) and also sets
       usWinAscent to be the sum of Ascender+Linegap and usWinDescent to be the negative of
       Descender.

   $t->guessRangeBits (\%map, [$cp_threshold, [%u_threshold]])
       Set the ulCodePageRange and ulUnicodeRange fields based on characters actually present in
       the font.

       %map is a hash keyed by USV returning non-zero for characters present (e.g. use {'val'} a
       from Unicode cmap).

       The two optional parameters are percentage of characters within the codepage or unicode
       range that need to be present to constitute coverage. A threshold of 0 causes
       corresponding range bits to be set if any characters are present at all, while a negative
       value causes the corresponding range bits to be unchanged. Defaults are 50 and 0,
       respectively.

       For codepage bits, the threshold is percentage of characters between 0xC0 and 0xFF that
       need to be present to constitute coverage). For codepages other than 1252, characters
       (e.g., punctuation) that are defined identically to cp1252 are ignored for the purposes of
       this percentage calculation. Looks only for SBCS codepages, not DBCS.

       For Unicode range bits that represent multiple ranges, e.g., bit 29 represents:

         Latin Extended Additional  1E00-1EFF
         Latin Extended-C           2C60-2C7F
         Latin Extended-D           A720-A7FF

       the bit will be set if any of these ranges meet the threshold requirement.

BUGS

       None known

AUTHOR

       Martin Hosken Martin_Hosken@sil.org.

LICENSING

       Copyright (c) 1998-2013, SIL International (http://www.sil.org)

       This module is released under the terms of the Artistic License 2.0.  For details, see the
       full text of the license in the file LICENSE.