Font::TTF::Silf(3)					User Contributed Perl Documentation					Font::TTF::Silf(3)

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 without 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 characterse 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

perl v5.16.3							    2012-05-19							Font::TTF::Silf(3)