freetype/truetype/glyph.go

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// Copyright 2010 The Freetype-Go Authors. All rights reserved.
// Use of this source code is governed by your choice of either the
// FreeType License or the GNU General Public License version 2 (or
// any later version), both of which can be found in the LICENSE file.
package truetype
import (
"golang.org/x/image/math/fixed"
)
// Hinting is the policy for snapping a glyph's contours to pixel boundaries.
type Hinting uint32
const (
// NoHinting means to not perform any hinting.
NoHinting Hinting = iota
// FullHinting means to use the font's hinting instructions.
FullHinting
// TODO: implement VerticalHinting.
)
// A Point is a co-ordinate pair plus whether it is 'on' a contour or an 'off'
// control point.
type Point struct {
X, Y fixed.Int26_6
// The Flags' LSB means whether or not this Point is 'on' the contour.
// Other bits are reserved for internal use.
Flags uint32
}
// A GlyphBuf holds a glyph's contours. A GlyphBuf can be re-used to load a
// series of glyphs from a Font.
type GlyphBuf struct {
// AdvanceWidth is the glyph's advance width.
AdvanceWidth fixed.Int26_6
// B is the glyph's bounding box.
B Bounds
// Point contains all Points from all contours of the glyph. If
// hinting was used to load a glyph then Unhinted contains those
// Points before they were hinted, and InFontUnits contains those
// Points before they were hinted and scaled.
Point, Unhinted, InFontUnits []Point
// End is the point indexes of the end point of each countour. The
// length of End is the number of contours in the glyph. The i'th
// contour consists of points Point[End[i-1]:End[i]], where End[-1]
// is interpreted to mean zero.
End []int
font *Font
scale fixed.Int26_6
hinting Hinting
hinter hinter
// phantomPoints are the co-ordinates of the synthetic phantom points
// used for hinting and bounding box calculations.
phantomPoints [4]Point
// pp1x is the X co-ordinate of the first phantom point. The '1' is
// using 1-based indexing; pp1x is almost always phantomPoints[0].X.
// TODO: eliminate this and consistently use phantomPoints[0].X.
pp1x fixed.Int26_6
// metricsSet is whether the glyph's metrics have been set yet. For a
// compound glyph, a sub-glyph may override the outer glyph's metrics.
metricsSet bool
// tmp is a scratch buffer.
tmp []Point
}
// Flags for decoding a glyph's contours. These flags are documented at
// http://developer.apple.com/fonts/TTRefMan/RM06/Chap6glyf.html.
const (
flagOnCurve = 1 << iota
flagXShortVector
flagYShortVector
flagRepeat
flagPositiveXShortVector
flagPositiveYShortVector
// The remaining flags are for internal use.
flagTouchedX
flagTouchedY
)
// The same flag bits (0x10 and 0x20) are overloaded to have two meanings,
// dependent on the value of the flag{X,Y}ShortVector bits.
const (
flagThisXIsSame = flagPositiveXShortVector
flagThisYIsSame = flagPositiveYShortVector
)
// Load loads a glyph's contours from a Font, overwriting any previously loaded
// contours for this GlyphBuf. scale is the number of 26.6 fixed point units in
// 1 em, i is the glyph index, and h is the hinting policy.
func (g *GlyphBuf) Load(f *Font, scale fixed.Int26_6, i Index, h Hinting) error {
g.Point = g.Point[:0]
g.Unhinted = g.Unhinted[:0]
g.InFontUnits = g.InFontUnits[:0]
g.End = g.End[:0]
g.font = f
g.hinting = h
g.scale = scale
g.pp1x = 0
g.phantomPoints = [4]Point{}
g.metricsSet = false
if h != NoHinting {
if err := g.hinter.init(f, scale); err != nil {
return err
}
}
if err := g.load(0, i, true); err != nil {
return err
}
// TODO: this selection of either g.pp1x or g.phantomPoints[0].X isn't ideal,
// and should be cleaned up once we have all the testScaling tests passing,
// plus additional tests for Freetype-Go's bounding boxes matching C Freetype's.
pp1x := g.pp1x
if h != NoHinting {
pp1x = g.phantomPoints[0].X
}
if pp1x != 0 {
for i := range g.Point {
g.Point[i].X -= pp1x
}
}
advanceWidth := g.phantomPoints[1].X - g.phantomPoints[0].X
if h != NoHinting {
if len(f.hdmx) >= 8 {
if n := u32(f.hdmx, 4); n > 3+uint32(i) {
for hdmx := f.hdmx[8:]; uint32(len(hdmx)) >= n; hdmx = hdmx[n:] {
if fixed.Int26_6(hdmx[0]) == scale>>6 {
advanceWidth = fixed.Int26_6(hdmx[2+i]) << 6
break
}
}
}
}
advanceWidth = (advanceWidth + 32) &^ 63
}
g.AdvanceWidth = advanceWidth
// Set g.B to the 'control box', which is the bounding box of the Bézier
// curves' control points. This is easier to calculate, no smaller than
// and often equal to the tightest possible bounding box of the curves
// themselves. This approach is what C Freetype does. We can't just scale
// the nominal bounding box in the glyf data as the hinting process and
// phantom point adjustment may move points outside of that box.
if len(g.Point) == 0 {
g.B = Bounds{}
} else {
p := g.Point[0]
g.B.XMin = p.X
g.B.XMax = p.X
g.B.YMin = p.Y
g.B.YMax = p.Y
for _, p := range g.Point[1:] {
if g.B.XMin > p.X {
g.B.XMin = p.X
} else if g.B.XMax < p.X {
g.B.XMax = p.X
}
if g.B.YMin > p.Y {
g.B.YMin = p.Y
} else if g.B.YMax < p.Y {
g.B.YMax = p.Y
}
}
// Snap the box to the grid, if hinting is on.
if h != NoHinting {
g.B.XMin &^= 63
g.B.YMin &^= 63
g.B.XMax += 63
g.B.XMax &^= 63
g.B.YMax += 63
g.B.YMax &^= 63
}
}
return nil
}
func (g *GlyphBuf) load(recursion uint32, i Index, useMyMetrics bool) (err error) {
// The recursion limit here is arbitrary, but defends against malformed glyphs.
if recursion >= 32 {
return UnsupportedError("excessive compound glyph recursion")
}
// Find the relevant slice of g.font.glyf.
var g0, g1 uint32
if g.font.locaOffsetFormat == locaOffsetFormatShort {
g0 = 2 * uint32(u16(g.font.loca, 2*int(i)))
g1 = 2 * uint32(u16(g.font.loca, 2*int(i)+2))
} else {
g0 = u32(g.font.loca, 4*int(i))
g1 = u32(g.font.loca, 4*int(i)+4)
}
// Decode the contour count and nominal bounding box, from the first
// 10 bytes of the glyf data. boundsYMin and boundsXMax, at offsets 4
// and 6, are unused.
glyf, ne, boundsXMin, boundsYMax := []byte(nil), 0, fixed.Int26_6(0), fixed.Int26_6(0)
if g0+10 <= g1 {
glyf = g.font.glyf[g0:g1]
ne = int(int16(u16(glyf, 0)))
boundsXMin = fixed.Int26_6(int16(u16(glyf, 2)))
boundsYMax = fixed.Int26_6(int16(u16(glyf, 8)))
}
// Create the phantom points.
uhm, pp1x := g.font.unscaledHMetric(i), fixed.Int26_6(0)
uvm := g.font.unscaledVMetric(i, boundsYMax)
g.phantomPoints = [4]Point{
{X: boundsXMin - uhm.LeftSideBearing},
{X: boundsXMin - uhm.LeftSideBearing + uhm.AdvanceWidth},
{X: uhm.AdvanceWidth / 2, Y: boundsYMax + uvm.TopSideBearing},
{X: uhm.AdvanceWidth / 2, Y: boundsYMax + uvm.TopSideBearing - uvm.AdvanceHeight},
}
if len(glyf) == 0 {
g.addPhantomsAndScale(len(g.Point), len(g.Point), true, true)
copy(g.phantomPoints[:], g.Point[len(g.Point)-4:])
g.Point = g.Point[:len(g.Point)-4]
return nil
}
// Load and hint the contours.
if ne < 0 {
if ne != -1 {
// http://developer.apple.com/fonts/TTRefMan/RM06/Chap6glyf.html says that
// "the values -2, -3, and so forth, are reserved for future use."
return UnsupportedError("negative number of contours")
}
pp1x = g.font.scale(g.scale * (boundsXMin - uhm.LeftSideBearing))
if err := g.loadCompound(recursion, uhm, i, glyf, useMyMetrics); err != nil {
return err
}
} else {
np0, ne0 := len(g.Point), len(g.End)
program := g.loadSimple(glyf, ne)
g.addPhantomsAndScale(np0, np0, true, true)
pp1x = g.Point[len(g.Point)-4].X
if g.hinting != NoHinting {
if len(program) != 0 {
err := g.hinter.run(
program,
g.Point[np0:],
g.Unhinted[np0:],
g.InFontUnits[np0:],
g.End[ne0:],
)
if err != nil {
return err
}
}
// Drop the four phantom points.
g.InFontUnits = g.InFontUnits[:len(g.InFontUnits)-4]
g.Unhinted = g.Unhinted[:len(g.Unhinted)-4]
}
if useMyMetrics {
copy(g.phantomPoints[:], g.Point[len(g.Point)-4:])
}
g.Point = g.Point[:len(g.Point)-4]
if np0 != 0 {
// The hinting program expects the []End values to be indexed relative
// to the inner glyph, not the outer glyph, so we delay adding np0 until
// after the hinting program (if any) has run.
for i := ne0; i < len(g.End); i++ {
g.End[i] += np0
}
}
}
if useMyMetrics && !g.metricsSet {
g.metricsSet = true
g.pp1x = pp1x
}
return nil
}
// loadOffset is the initial offset for loadSimple and loadCompound. The first
// 10 bytes are the number of contours and the bounding box.
const loadOffset = 10
func (g *GlyphBuf) loadSimple(glyf []byte, ne int) (program []byte) {
offset := loadOffset
for i := 0; i < ne; i++ {
g.End = append(g.End, 1+int(u16(glyf, offset)))
offset += 2
}
// Note the TrueType hinting instructions.
instrLen := int(u16(glyf, offset))
offset += 2
program = glyf[offset : offset+instrLen]
offset += instrLen
np0 := len(g.Point)
np1 := np0 + int(g.End[len(g.End)-1])
// Decode the flags.
for i := np0; i < np1; {
c := uint32(glyf[offset])
offset++
g.Point = append(g.Point, Point{Flags: c})
i++
if c&flagRepeat != 0 {
count := glyf[offset]
offset++
for ; count > 0; count-- {
g.Point = append(g.Point, Point{Flags: c})
i++
}
}
}
// Decode the co-ordinates.
var x int16
for i := np0; i < np1; i++ {
f := g.Point[i].Flags
if f&flagXShortVector != 0 {
dx := int16(glyf[offset])
offset++
if f&flagPositiveXShortVector == 0 {
x -= dx
} else {
x += dx
}
} else if f&flagThisXIsSame == 0 {
x += int16(u16(glyf, offset))
offset += 2
}
g.Point[i].X = fixed.Int26_6(x)
}
var y int16
for i := np0; i < np1; i++ {
f := g.Point[i].Flags
if f&flagYShortVector != 0 {
dy := int16(glyf[offset])
offset++
if f&flagPositiveYShortVector == 0 {
y -= dy
} else {
y += dy
}
} else if f&flagThisYIsSame == 0 {
y += int16(u16(glyf, offset))
offset += 2
}
g.Point[i].Y = fixed.Int26_6(y)
}
return program
}
func (g *GlyphBuf) loadCompound(recursion uint32, uhm HMetric, i Index,
glyf []byte, useMyMetrics bool) error {
// Flags for decoding a compound glyph. These flags are documented at
// http://developer.apple.com/fonts/TTRefMan/RM06/Chap6glyf.html.
const (
flagArg1And2AreWords = 1 << iota
flagArgsAreXYValues
flagRoundXYToGrid
flagWeHaveAScale
flagUnused
flagMoreComponents
flagWeHaveAnXAndYScale
flagWeHaveATwoByTwo
flagWeHaveInstructions
flagUseMyMetrics
flagOverlapCompound
)
np0, ne0 := len(g.Point), len(g.End)
offset := loadOffset
for {
flags := u16(glyf, offset)
component := Index(u16(glyf, offset+2))
dx, dy, transform, hasTransform := fixed.Int26_6(0), fixed.Int26_6(0), [4]int16{}, false
if flags&flagArg1And2AreWords != 0 {
dx = fixed.Int26_6(int16(u16(glyf, offset+4)))
dy = fixed.Int26_6(int16(u16(glyf, offset+6)))
offset += 8
} else {
dx = fixed.Int26_6(int16(int8(glyf[offset+4])))
dy = fixed.Int26_6(int16(int8(glyf[offset+5])))
offset += 6
}
if flags&flagArgsAreXYValues == 0 {
return UnsupportedError("compound glyph transform vector")
}
if flags&(flagWeHaveAScale|flagWeHaveAnXAndYScale|flagWeHaveATwoByTwo) != 0 {
hasTransform = true
switch {
case flags&flagWeHaveAScale != 0:
transform[0] = int16(u16(glyf, offset+0))
transform[3] = transform[0]
offset += 2
case flags&flagWeHaveAnXAndYScale != 0:
transform[0] = int16(u16(glyf, offset+0))
transform[3] = int16(u16(glyf, offset+2))
offset += 4
case flags&flagWeHaveATwoByTwo != 0:
transform[0] = int16(u16(glyf, offset+0))
transform[1] = int16(u16(glyf, offset+2))
transform[2] = int16(u16(glyf, offset+4))
transform[3] = int16(u16(glyf, offset+6))
offset += 8
}
}
savedPP := g.phantomPoints
np0 := len(g.Point)
componentUMM := useMyMetrics && (flags&flagUseMyMetrics != 0)
if err := g.load(recursion+1, component, componentUMM); err != nil {
return err
}
if flags&flagUseMyMetrics == 0 {
g.phantomPoints = savedPP
}
if hasTransform {
for j := np0; j < len(g.Point); j++ {
p := &g.Point[j]
newX := 0 +
fixed.Int26_6((int64(p.X)*int64(transform[0])+1<<13)>>14) +
fixed.Int26_6((int64(p.Y)*int64(transform[2])+1<<13)>>14)
newY := 0 +
fixed.Int26_6((int64(p.X)*int64(transform[1])+1<<13)>>14) +
fixed.Int26_6((int64(p.Y)*int64(transform[3])+1<<13)>>14)
p.X, p.Y = newX, newY
}
}
dx = g.font.scale(g.scale * dx)
dy = g.font.scale(g.scale * dy)
if flags&flagRoundXYToGrid != 0 {
dx = (dx + 32) &^ 63
dy = (dy + 32) &^ 63
}
for j := np0; j < len(g.Point); j++ {
p := &g.Point[j]
p.X += dx
p.Y += dy
}
// TODO: also adjust g.InFontUnits and g.Unhinted?
if flags&flagMoreComponents == 0 {
break
}
}
instrLen := 0
if g.hinting != NoHinting && offset+2 <= len(glyf) {
instrLen = int(u16(glyf, offset))
offset += 2
}
g.addPhantomsAndScale(np0, len(g.Point), false, instrLen > 0)
points, ends := g.Point[np0:], g.End[ne0:]
g.Point = g.Point[:len(g.Point)-4]
for j := range points {
points[j].Flags &^= flagTouchedX | flagTouchedY
}
if instrLen == 0 {
if !g.metricsSet {
copy(g.phantomPoints[:], points[len(points)-4:])
}
return nil
}
// Hint the compound glyph.
program := glyf[offset : offset+instrLen]
// Temporarily adjust the ends to be relative to this compound glyph.
if np0 != 0 {
for i := range ends {
ends[i] -= np0
}
}
// Hinting instructions of a composite glyph completely refer to the
// (already) hinted subglyphs.
g.tmp = append(g.tmp[:0], points...)
if err := g.hinter.run(program, points, g.tmp, g.tmp, ends); err != nil {
return err
}
if np0 != 0 {
for i := range ends {
ends[i] += np0
}
}
if !g.metricsSet {
copy(g.phantomPoints[:], points[len(points)-4:])
}
return nil
}
func (g *GlyphBuf) addPhantomsAndScale(np0, np1 int, simple, adjust bool) {
// Add the four phantom points.
g.Point = append(g.Point, g.phantomPoints[:]...)
// Scale the points.
if simple && g.hinting != NoHinting {
g.InFontUnits = append(g.InFontUnits, g.Point[np1:]...)
}
for i := np1; i < len(g.Point); i++ {
p := &g.Point[i]
p.X = g.font.scale(g.scale * p.X)
p.Y = g.font.scale(g.scale * p.Y)
}
if g.hinting == NoHinting {
return
}
// Round the 1st phantom point to the grid, shifting all other points equally.
// Note that "all other points" starts from np0, not np1.
// TODO: delete this adjustment and the np0/np1 distinction, when
// we update the compatibility tests to C Freetype 2.5.3.
// See http://git.savannah.gnu.org/cgit/freetype/freetype2.git/commit/?id=05c786d990390a7ca18e62962641dac740bacb06
if adjust {
pp1x := g.Point[len(g.Point)-4].X
if dx := ((pp1x + 32) &^ 63) - pp1x; dx != 0 {
for i := np0; i < len(g.Point); i++ {
g.Point[i].X += dx
}
}
}
if simple {
g.Unhinted = append(g.Unhinted, g.Point[np1:]...)
}
// Round the 2nd and 4th phantom point to the grid.
p := &g.Point[len(g.Point)-3]
p.X = (p.X + 32) &^ 63
p = &g.Point[len(g.Point)-1]
p.Y = (p.Y + 32) &^ 63
}
// TODO: is this necessary? The zero-valued GlyphBuf is perfectly usable.
// NewGlyphBuf returns a newly allocated GlyphBuf.
func NewGlyphBuf() *GlyphBuf {
return &GlyphBuf{
Point: make([]Point, 0, 256),
End: make([]int, 0, 32),
}
}