Provided by: libfont-ttf-perl_1.06-2_all bug

NAME

       Font::TTF::Silf - The main Graphite table

DESCRIPTION

       The Silf table holds the core of the Graphite rules for a font. A Silf table has
       potentially multiple silf subtables, although there is usually only one. Within a silf
       subtable, there are a number of passes which contain the actual finite state machines to
       match rules and the constraint and action code to be executed when a rule matches.

INSTANCE VARIABLES

       Version
           Silf table format version

       Compiler
           Lowest compiler version necessary to fully support the semantics expressed in this
           Graphite description

       SILF
           An array of Silf subtables

           maxGlyphID
               The maximum glyph id referenced including pseudo and non glyphs

           Ascent
               Extra ascent to be added to the font ascent.

           Descent
               Extra descent to be added to the font descent. Both values are assumed to be
               positive for a descender below the base line.

           substPass
               Pass index into PASS of the first substitution pass.

           posPass
               Pass index into PASS of the first positioning pass.

           justPass
               Pass index into PASS of the first justification pass.

           bidiPass
               Pass index of the pass before which the bidirectional processing pass will be
               executed.  0xFF indicates that there is no bidi pass to be executed.

           Flags
               A bitfield of flags:

                   0 - Indicates there are line end contextual rules in one of the passes

           maxPreContext
               Maximum length of a context preceding a cross line boundary contextualisation.

           maxPostContext
               Maximum length of a context following a cross line boundary contextualsation.

           attrPseudo
               Glyph attribute for the actual glyph id associated with a pseudo glyph.

           attrBreakWeight
               Glyph attribute number of the attribute holding the default breakweight associated
               with a glyph.

           attrDirectionality
               Glyph attribute number of the attribute holding the default directionality value
               associated with a glyph.

           JUST
               The may be a number of justification levels each with their own property values.
               This points to an array of hashes, one for each justification level.

               attrStretch
                   Glyph attribute number for the amount of stretch allowed before this glyph.

               attrShrink
                   Glyph attribute number for the amount of shrink allowed before this glyph.

               attrStep
                   Glyph attribute number specifying the minimum granularity of actual spacing
                   associated with this glyph at this level.

               attrWeight
                   Glyph attribute number giving the weight associated with spreading space
                   across a run of glyphs.

               runto
                   Which level starts the next stage.

           numLigComp
               Number of initial glyph attributes that represent ligature components

           numUserAttr
               Number of user defined slot attributes referenced. Tells the engine how much space
               to allocate to a slot for user attributes.

           maxCompPerLig
               Maximum number of components per ligature.

           direction
               Supported directions for this writing system

           CRIT_FEATURE
               Array of critical features.

           scripts
               Array of script tags that indicate which set of GDL rules to execute if there is
               more than one in a font.

           lbGID
               Glyph ID of the linebreak pseudo glyph.

           pseudos
               Hash of Unicode values to pseduo glyph ids.

           classes
               This is an array of classes, each of which is an array of glyph ids in class
               order.

           PASS
               The details of rules and actions are stored in passes. This value is an array of
               pass subobjects one for each pass.

               flags
                   This is a bitfield:

                       0 - If true, this pass makes no change to the slot stream considered as a sequence of glyph ids.
                           Only slot attributes are expected to change (for example during positioning).

               maxRuleLoop
                   How many times the engine will allow rules to be tested and run without the
                   engine advancing through the input slot stream.

               maxRuleContext
                   Number of slots of input needed to run this pass.

               maxBackup
                   Number of slots by which the following pass needs to trail this pass (i.e. the
                   maximum this pass is allowed to back up).

               numRules
                   Number of action code blocks, and so uncompressed rules, in this pass.

               numRows
                   Number of rows in the finite state machine.

               numTransitional
                   Number of rows in the finite state machine that are not final states. This
                   specifies the number of rows in the fsm element.

               numSuccess
                   Number of success states. A success state may also be a transitional state.

               numColumns
                   Number of columns in the finite state machine.

               colmap
                   A hash, indexed by glyphid, that gives the fsm column number associated with
                   that glyphid. If not present, then the glyphid is not part of the fsm and will
                   finish fsm processing if it occurs.

               rulemap
                   An array of arrays, one for each success state. Each array holds a list of
                   rule numbers associated with that state.

               minRulePreContext
                   Minimum number of items in a rule's precontext.

               maxRulePreContext
                   The maximum number of items in any rule's precontext.

               startStates
                   Array of starting state numbers dependeing on the length of actual precontext.
                   There are maxRulePreContext - minRulePreContext + 1 of these.

               ruleSortKeys
                   An array of sort keys one for each rule giving the length of the rule
                   including its precontext.

               rulePreContexts
                   An array of precontext lengths for each rule.

               fsm A two dimensional array such that $p->{'fsm'}[$row][$col] gives the row of the
                   next node to try in the fsm.

               passConstraintLen
                   Length in bytes of the passConstraint code.

               passConstraintCode
                   A byte string holding the pass constraint code.

               constraintCode
                   An array of byte strings holding the constraint code for each rule.

               actionCode
                   An array of byte strings holding the action code for each rule.

   @opcodes
       Each array holds the name of the opcode, the number of operand bytes and a string
       describing the operands.  The characters in the string have the following meaning:

           c - lsb of class id
           C - msb of class id
           f - feature index
           g - lsb of glyph attribute id
           G - msb of glyph attribute id
           l - lsb of a 32-bit extension to a 16-bit number
           L - msb of a 32-bit number
           m - glyph metric id
           n - lsb of a number
           N - msb of a 16-bit number
           o - offset (jump)
           s - slot reference
           S - slot attribute id
           v - variable number of following arguments

   read
       Reads the Silf table into the internal data structure

   out
       Outputs a Silf data structure to a font file in binary format

   $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.

AUTHOR

       Martin Hosken <http://scripts.sil.org/FontUtils>.

LICENSING

       Copyright (c) 1998-2016, 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.