table_silf.go

package graphite

import (
	"encoding/binary"
	"errors"
	"fmt"

	"github.com/benoitkugler/textlayout/fonts/binaryreader"
)

type tableSilf []passes

type silfSubtableHeaderV3 struct {
	RuleVersion   uint32 // Version of stack-machine language used in rules
	PassOffset    uint16 // offset of oPasses[0] relative to start of sub-table
	PseudosOffset uint16 // offset of pMaps[0] relative to start of sub-table
}

type silfSubtablePart1 struct {
	MaxGlyphID   uint16 // Maximum valid glyph ID (including line-break & pseudo-glyphs)
	ExtraAscent  int16  // Em-units to be added to the font’s ascent
	ExtraDescent int16  // Em-units to be added to the font’s descent
	NumPasses    byte   // Number of rendering description passes
	ISubst       byte   // Index of first substitution pass
	IPos         byte   // Index of first Positioning pass
	IJust        byte   // Index of first Justification pass
	IBidi        byte   // Index of first pass after the bidi pass(must be <= iPos); 0xFF implies no bidi pass
	// Bit 0: True (1) if there is any start-, end-, or cross-line contextualization
	// Bit 1: True (1) if cross-line contextualization can be ignored for optimization
	// Bits 2-4: space contextual flags
	// Bit 5: automatic collision fixing
	Flags          byte
	MaxPreContext  byte // Max range for preceding cross-line-boundary contextualization
	MaxPostContext byte // Max range for following cross-line-boundary contextualization

	AttrPseudo         byte // Glyph attribute number that is used for actual glyph ID for a pseudo glyph
	AttrBreakWeight    byte // Glyph attribute number of breakweight attribute
	AttrDirectionality byte // Glyph attribute number for directionality attribute
	AttrMirroring      byte // Glyph attribute number for mirror.glyph (mirror.isEncoded comes directly after)
	AttrSkipPasses     byte // Glyph attribute of bitmap indicating key glyphs for pass optimization
	NumJLevels         byte // Number of justification levels; 0 if no justification
}

type silfSubtablePart2 struct {
	NumLigComp     uint16 // Number of initial glyph attributes that represent ligature components
	NumUserDefn    byte   // Number of user-defined slot attributes
	MaxCompPerLig  byte   // Maximum number of components per ligature
	Direction      byte   // Supported direction(s)
	AttrCollisions byte   // Glyph attribute number for collision.flags attribute (several more collision attrs come after it...)

	_ [3]byte // reserved
}

type extractedPass struct {
	Rules   []extractedRule
	Context codeContext
}

type extractedRule struct {
	Action     []byte
	Constraint []byte
	SortKey    uint16
	PreContext uint8
}

func parseTableSilf(data []byte, numAttributes, numFeatures uint16) (tableSilf, error) {
	data, version, err := decompressTable(data)
	if err != nil {
		return nil, fmt.Errorf("invalid table Silf: %s", err)
	}

	r := binaryreader.NewReader(data)
	r.Skip(4)

	if version < 2 {
		return nil, fmt.Errorf("invalid table Silf version: %x", version)
	}
	if version >= 3 {
		r.Skip(4)
	}

	numSub, err := r.Uint16()
	if err != nil {
		return nil, fmt.Errorf("invalid table Silf: %s", err)
	}
	r.Skip(2) // reserved

	offsets, err := r.Uint32s(int(numSub))
	if err != nil {
		return nil, fmt.Errorf("invalid table Silf: %s", err)
	}

	out := make([]passes, numSub)
	for i, offset := range offsets {
		subtable, err := parseSubtableSilf(data, offset, version)
		if err != nil {
			return nil, fmt.Errorf("invalid silf subtable %d: %s", i, err)
		}

		out[i], err = newPasses(&subtable, numAttributes, numFeatures)
		if err != nil {
			return nil, fmt.Errorf("invalid silf subtable %d: %s", i, err)
		}
	}

	return out, nil
}

type pseudoMap struct {
	Unicode rune
	NPseudo gid
}

type silfSubtable struct {
	justificationLevels []justificationLevel // length NumJLevels
	scriptTags          []uint32
	classMap            classMap
	passes              []silfPass
	critFeatures        []uint16
	pseudoMap           []pseudoMap
	lbGID               uint16
	silfSubtablePart1
	silfSubtablePart2
}

// in-memory representation of the font subtable
// See pass for an higher-level object
type silfPass struct {
	ranges           []passRange // sorted by firstId
	ruleMap          [][]uint16  // with length NumSuccess, each sub array contains the rule numbers
	startStates      []uint16
	ruleSortKeys     []uint16   // with length numRules
	rulePreContext   []uint8    // with length numRules
	stateTransitions [][]uint16 // with length NumTransitional * NumColumns
	passConstraint   []byte
	ruleConstraints  [][]byte // with length numRules
	actions          [][]byte // with length numRules
	silfPassHeader
	collisionThreshold                   uint8
	minRulePreContext, maxRulePreContext byte
}

type binSearchHeader struct {
	NumRecord uint16
	_         [3]uint16 // ignored
}

func parseSubtableSilf(data []byte, offset uint32, version uint16) (out silfSubtable, err error) {
	if len(data) < int(offset) {
		return out, fmt.Errorf("invalid Silf subtable offset: %d", offset)
	}
	data = data[offset:] // needed for passes
	r := binaryreader.NewReader(data)

	var headerv3 silfSubtableHeaderV3
	if version >= 3 {
		err = r.ReadStruct(&headerv3)
		if err != nil {
			return out, fmt.Errorf("invalid Silf subtable: %s", err)
		}
	}
	err = r.ReadStruct(&out.silfSubtablePart1)
	if err != nil {
		return out, fmt.Errorf("invalid Silf subtable: %s", err)
	}

	out.justificationLevels = make([]justificationLevel, out.silfSubtablePart1.NumJLevels) // allocation guarded by the uint8 constraint
	err = r.ReadStruct(out.justificationLevels)
	if err != nil {
		return out, fmt.Errorf("invalid Silf subtable: %s", err)
	}

	err = r.ReadStruct(&out.silfSubtablePart2)
	if err != nil {
		return out, fmt.Errorf("invalid Silf subtable: %s", err)
	}

	numCritFeatures, err := r.Byte() // Number of critical features
	if err != nil {
		return out, fmt.Errorf("invalid Silf subtable: %s", err)
	}
	out.critFeatures, err = r.Uint16s(int(numCritFeatures))
	if err != nil {
		return out, fmt.Errorf("invalid Silf subtable: %s", err)
	}
	r.Skip(1) // byte reserved

	numScriptTag, err := r.Byte() // Number of scripts this subtable supports
	if err != nil {
		return out, fmt.Errorf("invalid Silf subtable: %s", err)
	}
	out.scriptTags, err = r.Uint32s(int(numScriptTag)) //  Array of numScriptTag script tags
	if err != nil {
		return out, fmt.Errorf("invalid Silf subtable: %s", err)
	}

	out.lbGID, err = r.Uint16() // Glyph ID for line-break psuedo-glyph
	if err != nil {
		return out, fmt.Errorf("invalid Silf subtable: %s", err)
	}

	oPasses, err := r.Uint32s(int(out.silfSubtablePart1.NumPasses) + 1) // Offets to passes relative to the start of this subtable
	if err != nil {
		return out, fmt.Errorf("invalid Silf subtable: %s", err)
	}

	var mapsHeader binSearchHeader
	err = r.ReadStruct(&mapsHeader)
	if err != nil {
		return out, fmt.Errorf("invalid Silf subtable: %s", err)
	}

	out.pseudoMap = make([]pseudoMap, mapsHeader.NumRecord) // Mappings between Unicode and pseudo-glyphs in order of Unicode
	err = r.ReadStruct(out.pseudoMap)
	if err != nil {
		return out, fmt.Errorf("invalid Silf subtable: %s", err)
	}

	out.classMap, err = parseGraphiteClassMap(r.Data(), version)
	if err != nil {
		return out, err
	}

	out.passes = make([]silfPass, out.silfSubtablePart1.NumPasses)
	for i := range out.passes {
		offset := oPasses[i]
		out.passes[i], err = parseSilfPass(data, offset)
		if err != nil {
			return out, err
		}
	}

	return out, nil
}

type justificationLevel struct {
	AttrStretch byte    //  Glyph attribute number for justify.X.stretch
	AttrShrink  byte    //  Glyph attribute number for justify.X.shrink
	AttrStep    byte    //  Glyph attribute number for justify.X.step
	AttrWeight  byte    //  Glyph attribute number for justify.X.weight
	Runto       byte    //  Which level starts the next stage
	_           [3]byte // reserved
}

type classMap struct {
	// numClass  uint16
	// numLinear uint16
	// oClass    []uint32      // Array of numClass + 1 offsets to class arrays from the beginning of the class map

	glyphs  [][]gid               // Glyphs for linear classes (length numLinear)
	lookups []graphiteLookupClass // An array of numClass – numLinear lookups
}

func (cl classMap) numClasses() uint16 { return uint16(len(cl.glyphs) + len(cl.lookups)) }

func (cl classMap) getClassGlyph(cid uint16, index int) GID {
	if int(cid) < len(cl.glyphs) { // linear
		if glyphs := cl.glyphs[cid]; index < len(glyphs) {
			return GID(glyphs[index])
		}
	} else if lookupIndex := int(cid) - len(cl.glyphs); lookupIndex < len(cl.lookups) {
		lookup := cl.lookups[lookupIndex]
		for _, entry := range lookup {
			if int(entry.Index) == index {
				return GID(entry.Glyph)
			}
		}
	}
	return 0
}

// returns -1 if not found
func (cl classMap) findClassIndex(cid uint16, gid_ GID) int {
	glyph := uint16(gid_)
	if int(cid) < len(cl.glyphs) { // linear
		for index, g := range cl.glyphs[cid] {
			if g == glyph {
				return index
			}
		}
	} else if lookupIndex := int(cid) - len(cl.glyphs); lookupIndex < len(cl.lookups) {
		lookup := cl.lookups[lookupIndex]
		for _, entry := range lookup {
			if entry.Glyph == glyph {
				return int(entry.Index)
			}
		}
	}
	return -1
}

// data starts at the class map
func parseGraphiteClassMap(data []byte, version uint16) (out classMap, err error) {
	r := binaryreader.NewReader(data)
	if len(data) < 4 {
		return out, errors.New("invalid Silf Class Map (EOF)")
	}
	numClass, _ := r.Uint16()  // Number of replacement classes
	numLinear, _ := r.Uint16() // Number of linearly stored replacement classes

	var offsets []uint32
	if version >= 4 {
		offsets, err = r.Uint32s(int(numClass) + 1)
		if err != nil {
			return out, fmt.Errorf("invalid Silf Class Map (with long offsets): %s", err)
		}
	} else {
		var slice []byte
		slice, err = r.FixedSizes(int(numClass)+1, 2)
		if err != nil {
			return out, fmt.Errorf("invalid Silf Class Map (with short offsets): %s", err)
		}
		offsets = make([]uint32, int(numClass)+1)
		for i := range offsets {
			offsets[i] = uint32(binary.BigEndian.Uint16(slice[2*i:]))
		}
	}

	if numClass < numLinear {
		return out, fmt.Errorf("invalid Silf Class Map (%d < %d)", numClass, numLinear)
	}

	out.glyphs = make([][]gid, numLinear)
	for i := range out.glyphs {
		start, end := offsets[i], offsets[i+1]
		if start > end {
			return out, fmt.Errorf("invalid Silf Class Map offset (%d > %d)", start, end)
		}

		out.glyphs[i] = make([]gid, (end-start)/2)
		r.SetPos(int(start))
		_ = r.ReadStruct(out.glyphs[i])
	}

	out.lookups = make([]graphiteLookupClass, numClass-numLinear)

	for i := range out.lookups {
		offset := int(offsets[int(numLinear)+i])
		r.SetPos(offset) // delay error checking
		out.lookups[i], err = parseGraphiteLookupClass(r)
		if err != nil {
			return out, err
		}
	}

	return out, nil
}

type graphiteLookupPair struct {
	Glyph gid
	Index uint16
}

type graphiteLookupClass []graphiteLookupPair

// r is positionned at the start
func parseGraphiteLookupClass(r *binaryreader.Reader) (graphiteLookupClass, error) {
	numsIDS, err := r.Uint16()
	if err != nil {
		return nil, fmt.Errorf("invalid Silf Lookup Class: %s", err)
	}
	r.Skip(6)
	out := make(graphiteLookupClass, numsIDS)
	err = r.ReadStruct(out)
	if err != nil {
		return nil, fmt.Errorf("invalid Silf Lookup Class: %s", err)
	}
	return out, nil
}

type silfPassHeader struct {
	// Bits 0-2: collision fixing max loop
	// Bits 3-4: auto kerning
	// Bit 5: flip direction 5.0 – added
	Flags           byte
	MaxRuleLoop     byte   // MaxRuleLoop for this pass
	MaxRuleContext  byte   // Number of slots of input needed to run this pass
	MaxBackup       byte   // Number of slots by which the following pass needs to trail this pass (ie, the maximum this pass is allowed to back up)
	NumRules        uint16 // Number of action code blocks
	FsmOffset       uint16 // offset to numRows relative to the beginning of the SIL_Pass block 2.0 – inserted ; 3.0 – use for fsmOffset
	PcCode          uint32 // Offset to start of pass constraint code from start of subtable (*passConstraints[0]*) 2.0 - added
	RcCode          uint32 // Offset to start of rule constraint code from start of subtable (*ruleConstraints[0]*)
	ACode           uint32 // Offset to start of action code relative to start of subtable (*actions[0]*)
	ODebug          uint32 // Offset to debug arrays (*dActions[0]*); equals 0 if debug stripped
	NumRows         uint16 // Number of FSM states
	NumTransitional uint16 // Number of transitional states in the FSM (length of *states* matrix)
	NumSuccess      uint16 // Number of success states in the FSM (size of *oRuleMap* array)
	NumColumns      uint16 // Number of FSM columns; 0 means no FSM
}

// performs some sanity checks.
func (s *silfPass) sanitize() error {
	if s.NumTransitional > s.NumRows {
		return fmt.Errorf("transitions, states : %d, %d", s.NumTransitional, s.NumRows)
	}
	if s.NumSuccess > s.NumRows {
		return fmt.Errorf("success, states : %d, %d", s.NumSuccess, s.NumRows)
	}
	if s.NumSuccess+s.NumTransitional < s.NumRows {
		return fmt.Errorf("success+transitions, states : %d, %d", s.NumSuccess+s.NumTransitional, s.NumRows)
	}
	if s.NumRules != 0 && len(s.ranges) == 0 {
		return errors.New("no ranges")
	}
	if s.NumColumns > 0x7FFF {
		return fmt.Errorf("columns : %d", s.NumColumns)
	}
	return nil
}

type passRange struct {
	FirstId gid    // First Glyph id in the range
	LastId  gid    // Last Glyph id in the range
	ColId   uint16 // Column index for this range
}

func parseSilfPass(data []byte, offset uint32) (out silfPass, err error) {
	r, err := binaryreader.NewReaderAt(data, offset)
	if err != nil {
		return out, fmt.Errorf("invalid Silf Pass offset: %s", err)
	}

	err = r.ReadStruct(&out.silfPassHeader) // length was checked
	if err != nil {
		return out, fmt.Errorf("invalid Silf Pass header: %s", err)
	}

	numRange, err := r.Uint16()
	if err != nil {
		return out, fmt.Errorf("invalid Silf Pass subtable: %s", err)
	}

	r.Skip(6)
	out.ranges = make([]passRange, numRange)
	err = r.ReadStruct(out.ranges)
	if err != nil {
		return out, fmt.Errorf("invalid Silf Pass subtable: %s", err)
	}

	oRuleMap, err := r.Uint16s(int(out.NumSuccess) + 1)
	if err != nil {
		return out, fmt.Errorf("invalid Silf Pass subtable: %s", err)
	}
	ruleMapSlice, err := r.Uint16s(int(oRuleMap[len(oRuleMap)-1]))
	if err != nil {
		return out, fmt.Errorf("invalid Silf Pass subtable: %s", err)
	}
	out.ruleMap = make([][]uint16, out.NumSuccess)
	for i := range out.ruleMap {
		start, end := oRuleMap[i], oRuleMap[i+1]
		if start > end || int(end) > len(ruleMapSlice) {
			continue
		}
		out.ruleMap[i] = ruleMapSlice[start:end]
	}

	out.minRulePreContext, err = r.Byte() // Minimum number of items in any rule’s context before the first modified rule item
	if err != nil {
		return out, fmt.Errorf("invalid Silf Pass subtable: %s", err)
	}
	out.maxRulePreContext, err = r.Byte() // Maximum number of items in any rule’s context before the first modified rule item
	if err != nil {
		return out, fmt.Errorf("invalid Silf Pass subtable: %s", err)
	}
	if out.maxRulePreContext < out.minRulePreContext {
		return out, fmt.Errorf("invalid Silf Pass subtable pre-context rule: (%d < %d)", out.maxRulePreContext, out.minRulePreContext)
	}
	out.startStates, err = r.Uint16s(int(out.maxRulePreContext-out.minRulePreContext) + 1)
	if err != nil {
		return out, fmt.Errorf("invalid Silf Pass subtable: %s", err)
	}

	out.ruleSortKeys, err = r.Uint16s(int(out.NumRules))
	if err != nil {
		return out, fmt.Errorf("invalid Silf Pass subtable: %s", err)
	}

	out.rulePreContext, err = r.FixedSizes(int(out.NumRules), 1)
	if err != nil {
		return out, fmt.Errorf("invalid Silf Pass subtable: %s", err)
	}

	out.collisionThreshold, err = r.Byte()
	if err != nil {
		return out, fmt.Errorf("invalid Silf Pass subtable: %s", err)
	}

	pConstraint, err := r.Uint16()
	if err != nil {
		return out, fmt.Errorf("invalid Silf Pass subtable: %s", err)
	}

	oConstraints, err := r.Uint16s(int(out.NumRules) + 1)
	if err != nil {
		return out, fmt.Errorf("invalid Silf Pass subtable: %s", err)
	}

	oActions, err := r.Uint16s(int(out.NumRules) + 1)
	if err != nil {
		return out, fmt.Errorf("invalid Silf Pass subtable: %s", err)
	}

	transitions, err := r.Uint16s(int(out.NumTransitional) * int(out.NumColumns))
	if err != nil {
		return out, fmt.Errorf("invalid Silf Pass subtable: %s", err)
	}
	out.stateTransitions = make([][]uint16, out.NumTransitional)
	for i := range out.stateTransitions {
		out.stateTransitions[i] = transitions[i*int(out.NumColumns) : (i+1)*int(out.NumColumns)]
	}

	r.Skip(1)

	out.passConstraint, err = r.FixedSizes(int(pConstraint), 1)
	if err != nil {
		return out, fmt.Errorf("invalid Silf Pass subtable: %s", err)
	}

	out.ruleConstraints = make([][]byte, out.NumRules)
	// resolve 0 value offsets
	for i := len(oConstraints) - 2; i >= 0; i-- {
		if oConstraints[i] == 0 {
			oConstraints[i] = oConstraints[i+1]
		}
	}

	ruleConstraintsSlice := r.Data()
	for i := range out.ruleConstraints {
		offsetStart, offsetEnd := oConstraints[i], oConstraints[i+1]
		if offsetStart == 0 || offsetEnd <= offsetStart {
			continue
		}
		if int(offsetEnd) > len(ruleConstraintsSlice) {
			return out, fmt.Errorf("invalid Silf Pass subtable rule constraint offset: %d", offsetEnd)
		}
		out.ruleConstraints[i] = ruleConstraintsSlice[offsetStart:offsetEnd]
	}

	out.actions = make([][]byte, out.NumRules)
	actionsSlice := ruleConstraintsSlice[oConstraints[len(oConstraints)-1]:]
	for i := range out.actions {
		offsetStart, offsetEnd := oActions[i], oActions[i+1]
		if offsetEnd <= offsetStart {
			continue
		}
		if int(offsetEnd) > len(actionsSlice) {
			return out, fmt.Errorf("invalid Silf Pass subtable rule constraint offset: %d", offsetEnd)
		}
		out.actions[i] = actionsSlice[offsetStart:offsetEnd]
	}
	return out, nil
}