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deps,text,widget,font/opentype: [API] add harfbuzz-powered text shaper

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This commit introduces a new text shaping infrastructure
powered by Benoit Kugler's Go source-port of harfbuzz.
This shaper can properly display complex scripts and RTL
text. This commit changes the signature of the text.Shaper
function, which is a breaking API change.

The new functionality is available via opentype.ParseHarfbuzz,
which configures a text.Shaper leveraging the new backend.

References: https://todo.sr.ht/~eliasnaur/gio/146
Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>
This commit is contained in:
Chris Waldon
2022-03-16 16:01:33 -04:00
committed by Elias Naur
parent db82d12372
commit 1e5a3696f5
12 changed files with 3009 additions and 143 deletions
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font/opentype/opentype.go
+125 -19
View File
@@ -6,20 +6,75 @@ package opentype
import (
"bytes"
"fmt"
"image"
"io"
"unicode"
"unicode/utf8"
"github.com/benoitkugler/textlayout/fonts"
"github.com/benoitkugler/textlayout/fonts/truetype"
"github.com/benoitkugler/textlayout/harfbuzz"
"github.com/go-text/typesetting/shaping"
"golang.org/x/image/font"
"golang.org/x/image/font/sfnt"
"golang.org/x/image/math/fixed"
"gioui.org/f32"
"gioui.org/font/opentype/internal"
"gioui.org/io/system"
"gioui.org/op"
"gioui.org/op/clip"
"gioui.org/text"
)
// HarfbuzzFont implements the text.Shaper interface using a rich text
// shaping engine.
type HarfbuzzFont struct {
font *truetype.Font
}
// ParseHarfbuzz constructs a HarfbuzzFont from source bytes.
func ParseHarfbuzz(src []byte) (*HarfbuzzFont, error) {
face, err := truetype.Parse(bytes.NewReader(src))
if err != nil {
return nil, fmt.Errorf("failed parsing truetype font: %w", err)
}
return &HarfbuzzFont{
font: face,
}, nil
}
func (f *HarfbuzzFont) Layout(ppem fixed.Int26_6, maxWidth int, lc system.Locale, txt io.RuneReader) ([]text.Line, error) {
return internal.Document(shaping.Shape, f.font, ppem, maxWidth, lc, txt), nil
}
func (f *HarfbuzzFont) Shape(ppem fixed.Int26_6, str text.Layout) clip.PathSpec {
return harfbuzzTextPath(ppem, f, str)
}
func (f *HarfbuzzFont) Metrics(ppem fixed.Int26_6) font.Metrics {
metrics := font.Metrics{}
font := harfbuzz.NewFont(f.font)
font.XScale = int32(ppem.Ceil()) << 6
font.YScale = font.XScale
// Use any horizontal direction.
fontExtents := font.ExtentsForDirection(harfbuzz.LeftToRight)
ascender := fixed.I(int(fontExtents.Ascender * 64))
descender := fixed.I(int(fontExtents.Descender * 64))
gap := fixed.I(int(fontExtents.LineGap * 64))
metrics.Height = ascender + descender + gap
metrics.Ascent = ascender
metrics.Descent = descender
// These three are not readily available.
// TODO(whereswaldon): figure out how to get these values.
metrics.XHeight = ascender
metrics.CapHeight = ascender
metrics.CaretSlope = image.Pt(0, 1)
return metrics
}
// Font implements text.Face. Its methods are safe to use
// concurrently.
type Font struct {
@@ -109,7 +164,7 @@ func (c *Collection) Font(i int) (*Font, error) {
return &Font{font: c.fonts[i].Font}, nil
}
func (f *Font) Layout(ppem fixed.Int26_6, maxWidth int, txt io.Reader) ([]text.Line, error) {
func (f *Font) Layout(ppem fixed.Int26_6, maxWidth int, lc system.Locale, txt io.RuneReader) ([]text.Line, error) {
glyphs, err := readGlyphs(txt)
if err != nil {
return nil, err
@@ -130,7 +185,7 @@ func (f *Font) Metrics(ppem fixed.Int26_6) font.Metrics {
return o.Metrics(&buf, ppem)
}
func (c *Collection) Layout(ppem fixed.Int26_6, maxWidth int, txt io.Reader) ([]text.Line, error) {
func (c *Collection) Layout(ppem fixed.Int26_6, maxWidth int, lc system.Locale, txt io.RuneReader) ([]text.Line, error) {
glyphs, err := readGlyphs(txt)
if err != nil {
return nil, err
@@ -325,31 +380,82 @@ func textPath(buf *sfnt.Buffer, ppem fixed.Int26_6, fonts []*opentype, str text.
return builder.End()
}
func readGlyphs(r io.Reader) ([]glyph, error) {
func harfbuzzTextPath(ppem fixed.Int26_6, font *HarfbuzzFont, str text.Layout) clip.PathSpec {
var lastPos f32.Point
var builder clip.Path
ops := new(op.Ops)
var x fixed.Int26_6
builder.Begin(ops)
rune := 0
ppemInt := ppem.Round()
ppem16 := uint16(ppemInt)
scaleFactor := float32(ppemInt) / float32(font.font.Upem())
for _, g := range str.Glyphs {
advance := g.XAdvance
outline, ok := font.font.GlyphData(g.ID, ppem16, ppem16).(fonts.GlyphOutline)
if !ok {
continue
}
// Move to glyph position.
pos := f32.Point{
X: float32(x)/64 - float32(g.XOffset)/64,
Y: -float32(g.YOffset) / 64,
}
builder.Move(pos.Sub(lastPos))
lastPos = pos
var lastArg f32.Point
// Convert sfnt.Segments to relative segments.
for _, fseg := range outline.Segments {
nargs := 1
switch fseg.Op {
case fonts.SegmentOpQuadTo:
nargs = 2
case fonts.SegmentOpCubeTo:
nargs = 3
}
var args [3]f32.Point
for i := 0; i < nargs; i++ {
a := f32.Point{
X: fseg.Args[i].X * scaleFactor,
Y: -fseg.Args[i].Y * scaleFactor,
}
args[i] = a.Sub(lastArg)
if i == nargs-1 {
lastArg = a
}
}
switch fseg.Op {
case fonts.SegmentOpMoveTo:
builder.Move(args[0])
case fonts.SegmentOpLineTo:
builder.Line(args[0])
case fonts.SegmentOpQuadTo:
builder.Quad(args[0], args[1])
case fonts.SegmentOpCubeTo:
builder.Cube(args[0], args[1], args[2])
default:
panic("unsupported segment op")
}
}
lastPos = lastPos.Add(lastArg)
x += advance
rune++
}
return builder.End()
}
func readGlyphs(r io.RuneReader) ([]glyph, error) {
var glyphs []glyph
buf := make([]byte, 0, 1024)
for {
n, err := r.Read(buf[len(buf):cap(buf)])
buf = buf[:len(buf)+n]
lim := len(buf)
// Read full runes if possible.
if err != io.EOF {
lim -= utf8.UTFMax - 1
}
i := 0
for i < lim {
c, s := utf8.DecodeRune(buf[i:])
i += s
glyphs = append(glyphs, glyph{Rune: c})
}
n = copy(buf, buf[i:])
buf = buf[:n]
c, _, err := r.ReadRune()
if err != nil {
if err == io.EOF {
break
}
return nil, err
}
glyphs = append(glyphs, glyph{Rune: c})
}
return glyphs, nil
}