graphite2_shaper.go

package harfbuzz

import (
	"strings"

	"github.com/benoitkugler/textlayout/fonts"
	"github.com/benoitkugler/textlayout/fonts/truetype"
	tt "github.com/benoitkugler/textlayout/fonts/truetype"
	"github.com/benoitkugler/textlayout/graphite"
)

// ported from harfbuzz/src/hb-graphite2.cc
// Copyright © 2011  Martin Hosken
// Copyright © 2011  SIL International
// Copyright © 2011,2012  Google, Inc.  Behdad Esfahbod

var _ shaper = (*shaperGraphite)(nil)

type graphite2Cluster struct {
	baseChar  int
	numChars  int
	baseGlyph int
	numGlyphs int
	cluster   int
	advance   float32
}

// shaperGraphite implements a shaper using Graphite features.
type shaperGraphite graphite.GraphiteFace

func (shaperGraphite) kind() shaperKind { return skGraphite }

func (shaperGraphite) compile(props SegmentProperties, userFeatures []Feature) {}

// Converts a string into a Tag. Valid tags
// are four characters. Shorter input strings will be
// padded with spaces. Longer input strings will be
// truncated.
// The empty string is mapped to 0.
func tagFromString(str string) truetype.Tag {
	if str == "" {
		return 0
	}
	var chars [4]byte

	if len(str) > 4 {
		str = str[:4]
	}
	copy(chars[:], str)
	for i := len(str); i < 4; i++ {
		chars[i] = ' '
	}

	return tt.NewTag(chars[0], chars[1], chars[2], chars[3])
}

func (sh *shaperGraphite) shape(font *Font, buffer *Buffer, features []Feature) {
	grface := (*graphite.GraphiteFace)(sh)

	lang := languageToString(buffer.Props.Language)
	var tagLang truetype.Tag
	if lang != "" {
		tagLang = tagFromString(strings.Split(lang, "-")[0])
	}
	feats := grface.FeaturesForLang(tagLang)

	for _, feature := range features {
		if fref := feats.FindFeature(feature.Tag); fref != nil {
			fref.Value = int16(feature.Value)
		}
	}

	chars := make([]rune, len(buffer.Info))
	for i, info := range buffer.Info {
		chars[i] = info.codepoint
	}

	scriptTag, _ := NewOTTagsFromScriptAndLanguage(buffer.Props.Script, "")
	tagScript := tagDefaultScript
	if len(scriptTag) != 0 {
		tagScript = scriptTag[len(scriptTag)-1]
	}
	dirMask := int8(2 | 0)
	if buffer.Props.Direction == RightToLeft {
		dirMask = 2 | 1
	}

	seg := grface.Shape(nil, chars, tagScript, feats, dirMask)

	if seg.NumGlyphs == 0 {
		buffer.Clear()
		return
	}

	clusters := make([]graphite2Cluster, len(buffer.Info))
	glyphs := make([]fonts.GID, seg.NumGlyphs)
	if L := seg.NumGlyphs - len(buffer.Info); L > 0 {
		// grow the storage
		buffer.Info = append(buffer.Info, make([]GlyphInfo, L)...)
		buffer.Pos = append(buffer.Pos, make([]GlyphPosition, L)...)
	} else {
		buffer.Info = buffer.Info[:seg.NumGlyphs]
		buffer.Pos = buffer.Pos[:seg.NumGlyphs]
	}

	clusters[0].cluster = buffer.Info[0].Cluster
	upem := font.faceUpem
	xscale := float32(font.XScale / upem)
	yscale := float32(font.YScale / upem)
	yscale *= yscale / xscale
	var curradv float32
	if buffer.Props.Direction.isBackward() {
		curradv = seg.First.Position.X * xscale
		clusters[0].advance = seg.Advance.X*xscale - curradv
	} else {
		clusters[0].advance = 0
	}
	var ci int
	for is, ic := seg.First, 0; is != nil; is, ic = is.Next, ic+1 {
		before := is.Before
		after := is.After
		glyphs[ic] = is.GID()
		for clusters[ci].baseChar > before && ci != 0 {
			clusters[ci-1].numChars += clusters[ci].numChars
			clusters[ci-1].numGlyphs += clusters[ci].numGlyphs
			clusters[ci-1].advance += clusters[ci].advance
			ci--
		}

		if is.CanInsertBefore() && clusters[ci].numChars != 0 && before >= clusters[ci].baseChar+clusters[ci].numChars {
			c := &clusters[ci+1]
			c.baseChar = clusters[ci].baseChar + clusters[ci].numChars
			c.cluster = buffer.Info[c.baseChar].Cluster
			c.numChars = before - c.baseChar
			c.baseGlyph = ic
			c.numGlyphs = 0
			if buffer.Props.Direction.isBackward() {
				c.advance = curradv - is.Position.X*xscale
				curradv -= c.advance
			} else {
				c.advance = 0
				clusters[ci].advance += is.Position.X*xscale - curradv
				curradv += clusters[ci].advance
			}
			ci++
		}
		clusters[ci].numGlyphs++

		if clusters[ci].baseChar+clusters[ci].numChars < after+1 {
			clusters[ci].numChars = after + 1 - clusters[ci].baseChar
		}
	}

	if buffer.Props.Direction.isBackward() {
		clusters[ci].advance += curradv
	} else {
		clusters[ci].advance += seg.Advance.X*xscale - curradv
	}
	ci++

	for i := 0; i < ci; i++ {
		for j := 0; j < clusters[i].numGlyphs; j++ {
			info := &buffer.Info[clusters[i].baseGlyph+j]
			info.Glyph = glyphs[clusters[i].baseGlyph+j]
			info.Cluster = clusters[i].cluster
			info.setInt32(int32(clusters[i].advance)) // all glyphs in the cluster get the same advance
		}
	}

	/* Positioning. */
	currclus := maxInt
	info := buffer.Info
	pPos := buffer.Pos
	if !buffer.Props.Direction.isBackward() {
		var curradvx, curradvy int32
		for is, index := seg.First, 0; is != nil; index, is = index+1, is.Next {
			pPos := &pPos[index]
			info := &info[index]
			pPos.XOffset = int32(is.Position.X*xscale) - curradvx
			pPos.YOffset = int32(is.Position.Y*yscale) - curradvy
			if info.Cluster != currclus {
				pPos.XAdvance = info.getInt32()
				curradvx += pPos.XAdvance
				currclus = info.Cluster
			} else {
				pPos.XAdvance = 0.
			}

			pPos.YAdvance = int32(is.Advance.Y * yscale)
			curradvy += pPos.YAdvance
		}
	} else {
		curradvx := int32(seg.Advance.X * xscale)
		var curradvy int32
		for is, index := seg.First, 0; is != nil; index, is = index+1, is.Next {
			pPos := &pPos[index]
			info := &info[index]
			if info.Cluster != currclus {
				pPos.XAdvance = info.getInt32()
				curradvx -= pPos.XAdvance
				currclus = info.Cluster
			} else {
				pPos.XAdvance = 0.
			}

			pPos.YAdvance = int32(is.Advance.Y * yscale)
			curradvy -= pPos.YAdvance
			pPos.XOffset = int32(is.Position.X*xscale) - info.getInt32() - curradvx + pPos.XAdvance
			pPos.YOffset = int32(is.Position.Y*yscale) - curradvy
		}
		buffer.reverseClusters()
	}

	buffer.clearGlyphFlags(GlyphUnsafeToBreak)
}