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Unified Diff: freetype/truetype/glyph.go

Issue 6201052: code review 6201052: freetype: re-organize the freetype/truetype package int... (Closed)
Patch Set: diff -r 5f15df395cc7 https://code.google.com/p/freetype-go Created 12 years, 8 months ago
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Index: freetype/truetype/glyph.go
===================================================================
copy from freetype/truetype/truetype.go
copy to freetype/truetype/glyph.go
--- a/freetype/truetype/truetype.go
+++ b/freetype/truetype/glyph.go
@@ -3,452 +3,8 @@
// FreeType License or the GNU General Public License version 2 (or
// any later version), both of which can be found in the LICENSE file.
-// The truetype package provides a parser for the TTF and TTC file formats.
-// Those formats are documented at http://developer.apple.com/fonts/TTRefMan/
-// and http://www.microsoft.com/typography/otspec/
-//
-// All numbers (e.g. bounds, point co-ordinates, font metrics) are measured in
-// FUnits. To convert from FUnits to pixels, scale by
-// (pointSize * resolution) / (font.UnitsPerEm() * 72dpi)
-// For example, 550 FUnits at 18pt, 72dpi and 2048upe is 4.83 pixels.
package truetype
-import (
- "fmt"
-)
-
-// An Index is a Font's index of a rune.
-type Index uint16
-
-// A Bounds holds the co-ordinate range of one or more glyphs.
-// The endpoints are inclusive.
-type Bounds struct {
- XMin, YMin, XMax, YMax int16
-}
-
-// An HMetric holds the horizontal metrics of a single glyph.
-type HMetric struct {
- AdvanceWidth uint16
- LeftSideBearing int16
-}
-
-// A FormatError reports that the input is not a valid TrueType font.
-type FormatError string
-
-func (e FormatError) Error() string {
- return "freetype: invalid TrueType format: " + string(e)
-}
-
-// An UnsupportedError reports that the input uses a valid but unimplemented
-// TrueType feature.
-type UnsupportedError string
-
-func (e UnsupportedError) Error() string {
- return "freetype: unsupported TrueType feature: " + string(e)
-}
-
-// data interprets a byte slice as a stream of integer values.
-type data []byte
-
-// u32 returns the next big-endian uint32.
-func (d *data) u32() uint32 {
- x := uint32((*d)[0])<<24 | uint32((*d)[1])<<16 | uint32((*d)[2])<<8 | uint32((*d)[3])
- *d = (*d)[4:]
- return x
-}
-
-// u16 returns the next big-endian uint16.
-func (d *data) u16() uint16 {
- x := uint16((*d)[0])<<8 | uint16((*d)[1])
- *d = (*d)[2:]
- return x
-}
-
-// u8 returns the next uint8.
-func (d *data) u8() uint8 {
- x := (*d)[0]
- *d = (*d)[1:]
- return x
-}
-
-// skip skips the next n bytes.
-func (d *data) skip(n int) {
- *d = (*d)[n:]
-}
-
-// readTable returns a slice of the TTF data given by a table's directory entry.
-func readTable(ttf []byte, offsetLength []byte) ([]byte, error) {
- d := data(offsetLength)
- offset := int(d.u32())
- if offset < 0 {
- return nil, FormatError(fmt.Sprintf("offset too large: %d", uint32(offset)))
- }
- length := int(d.u32())
- if length < 0 {
- return nil, FormatError(fmt.Sprintf("length too large: %d", uint32(length)))
- }
- end := offset + length
- if end < 0 || end > len(ttf) {
- return nil, FormatError(fmt.Sprintf("offset + length too large: %d", uint32(offset)+uint32(length)))
- }
- return ttf[offset:end], nil
-}
-
-const (
- locaOffsetFormatUnknown int = iota
- locaOffsetFormatShort
- locaOffsetFormatLong
-)
-
-// A cm holds a parsed cmap entry.
-type cm struct {
- start, end, delta, offset uint16
-}
-
-// A Font represents a Truetype font.
-type Font struct {
- // Tables sliced from the TTF data. The different tables are documented
- // at http://developer.apple.com/fonts/TTRefMan/RM06/Chap6.html
- cmap, glyf, head, hhea, hmtx, kern, loca, maxp []byte
- cmapIndexes []byte
-
- // Cached values derived from the raw ttf data.
- cm []cm
- locaOffsetFormat int
- nGlyph, nHMetric, nKern int
- unitsPerEm int
- bounds Bounds
-}
-
-func (f *Font) parseCmap() error {
- const (
- cmapFormat4 = 4
- languageIndependent = 0
-
- // A 32-bit encoding consists of a most-significant 16-bit Platform ID and a
- // least-significant 16-bit Platform Specific ID.
- unicodeEncoding = 0x00000003 // PID = 0 (Unicode), PSID = 3 (Unicode 2.0)
- microsoftEncoding = 0x00030001 // PID = 3 (Microsoft), PSID = 1 (UCS-2)
- )
-
- if len(f.cmap) < 4 {
- return FormatError("cmap too short")
- }
- d := data(f.cmap[2:])
- nsubtab := int(d.u16())
- if len(f.cmap) < 8*nsubtab+4 {
- return FormatError("cmap too short")
- }
- offset, found := 0, false
- for i := 0; i < nsubtab; i++ {
- // We read the 16-bit Platform ID and 16-bit Platform Specific ID as a single uint32.
- // All values are big-endian.
- pidPsid, o := d.u32(), d.u32()
- // We prefer the Unicode cmap encoding. Failing to find that, we fall
- // back onto the Microsoft cmap encoding.
- if pidPsid == unicodeEncoding {
- offset, found = int(o), true
- break
- } else if pidPsid == microsoftEncoding {
- offset, found = int(o), true
- // We don't break out of the for loop, so that Unicode can override Microsoft.
- }
- }
- if !found {
- return UnsupportedError("cmap encoding")
- }
- if offset <= 0 || offset > len(f.cmap) {
- return FormatError("bad cmap offset")
- }
-
- d = data(f.cmap[offset:])
- cmapFormat := d.u16()
- if cmapFormat != cmapFormat4 {
- return UnsupportedError(fmt.Sprintf("cmap format: %d", cmapFormat))
- }
- d.skip(2)
- language := d.u16()
- if language != languageIndependent {
- return UnsupportedError(fmt.Sprintf("language: %d", language))
- }
- segCountX2 := int(d.u16())
- if segCountX2%2 == 1 {
- return FormatError(fmt.Sprintf("bad segCountX2: %d", segCountX2))
- }
- segCount := segCountX2 / 2
- d.skip(6)
- f.cm = make([]cm, segCount)
- for i := 0; i < segCount; i++ {
- f.cm[i].end = d.u16()
- }
- d.skip(2)
- for i := 0; i < segCount; i++ {
- f.cm[i].start = d.u16()
- }
- for i := 0; i < segCount; i++ {
- f.cm[i].delta = d.u16()
- }
- for i := 0; i < segCount; i++ {
- f.cm[i].offset = d.u16()
- }
- f.cmapIndexes = []byte(d)
- return nil
-}
-
-func (f *Font) parseHead() error {
- if len(f.head) != 54 {
- return FormatError(fmt.Sprintf("bad head length: %d", len(f.head)))
- }
- d := data(f.head[18:])
- f.unitsPerEm = int(d.u16())
- d.skip(16)
- f.bounds.XMin = int16(d.u16())
- f.bounds.YMin = int16(d.u16())
- f.bounds.XMax = int16(d.u16())
- f.bounds.YMax = int16(d.u16())
- d.skip(6)
- switch i := d.u16(); i {
- case 0:
- f.locaOffsetFormat = locaOffsetFormatShort
- case 1:
- f.locaOffsetFormat = locaOffsetFormatLong
- default:
- return FormatError(fmt.Sprintf("bad indexToLocFormat: %d", i))
- }
- return nil
-}
-
-func (f *Font) parseHhea() error {
- if len(f.hhea) != 36 {
- return FormatError(fmt.Sprintf("bad hhea length: %d", len(f.hhea)))
- }
- d := data(f.hhea[34:])
- f.nHMetric = int(d.u16())
- if 4*f.nHMetric+2*(f.nGlyph-f.nHMetric) != len(f.hmtx) {
- return FormatError(fmt.Sprintf("bad hmtx length: %d", len(f.hmtx)))
- }
- return nil
-}
-
-func (f *Font) parseKern() error {
- // Apple's TrueType documentation (http://developer.apple.com/fonts/TTRefMan/RM06/Chap6kern.html) says:
- // "Previous versions of the 'kern' table defined both the version and nTables fields in the header
- // as UInt16 values and not UInt32 values. Use of the older format on the Mac OS is discouraged
- // (although AAT can sense an old kerning table and still make correct use of it). Microsoft
- // Windows still uses the older format for the 'kern' table and will not recognize the newer one.
- // Fonts targeted for the Mac OS only should use the new format; fonts targeted for both the Mac OS
- // and Windows should use the old format."
- // Since we expect that almost all fonts aim to be Windows-compatible, we only parse the "older" format,
- // just like the C Freetype implementation.
- if len(f.kern) == 0 {
- if f.nKern != 0 {
- return FormatError("bad kern table length")
- }
- return nil
- }
- if len(f.kern) < 18 {
- return FormatError("kern data too short")
- }
- d := data(f.kern[0:])
- version := d.u16()
- if version != 0 {
- return UnsupportedError(fmt.Sprintf("kern version: %d", version))
- }
- n := d.u16()
- if n != 1 {
- return UnsupportedError(fmt.Sprintf("kern nTables: %d", n))
- }
- d.skip(2)
- length := int(d.u16())
- coverage := d.u16()
- if coverage != 0x0001 {
- // We only support horizontal kerning.
- return UnsupportedError(fmt.Sprintf("kern coverage: 0x%04x", coverage))
- }
- f.nKern = int(d.u16())
- if 6*f.nKern != length-14 {
- return FormatError("bad kern table length")
- }
- return nil
-}
-
-func (f *Font) parseMaxp() error {
- if len(f.maxp) != 32 {
- return FormatError(fmt.Sprintf("bad maxp length: %d", len(f.maxp)))
- }
- d := data(f.maxp[4:])
- f.nGlyph = int(d.u16())
- return nil
-}
-
-// Bounds returns the union of a Font's glyphs' bounds.
-func (f *Font) Bounds() Bounds {
- return f.bounds
-}
-
-// UnitsPerEm returns the number of FUnits in a Font's em-square.
-func (f *Font) UnitsPerEm() int {
- return f.unitsPerEm
-}
-
-// Index returns a Font's index for the given rune.
-func (f *Font) Index(x rune) Index {
- c := uint16(x)
- n := len(f.cm)
- for i := 0; i < n; i++ {
- if f.cm[i].start <= c && c <= f.cm[i].end {
- if f.cm[i].offset == 0 {
- return Index(c + f.cm[i].delta)
- }
- offset := int(f.cm[i].offset) + 2*(i-n+int(c-f.cm[i].start))
- d := data(f.cmapIndexes[offset:])
- return Index(d.u16())
- }
- }
- return Index(0)
-}
-
-// HMetric returns the horizontal metrics for the glyph with the given index.
-func (f *Font) HMetric(i Index) HMetric {
- j := int(i)
- if j >= f.nGlyph {
- return HMetric{}
- }
- if j >= f.nHMetric {
- var hm HMetric
- p := 4 * (f.nHMetric - 1)
- d := data(f.hmtx[p:])
- hm.AdvanceWidth = d.u16()
- p += 2*(j-f.nHMetric) + 4
- d = data(f.hmtx[p:])
- hm.LeftSideBearing = int16(d.u16())
- return hm
- }
- d := data(f.hmtx[4*j:])
- return HMetric{d.u16(), int16(d.u16())}
-}
-
-// Kerning returns the kerning for the given glyph pair.
-func (f *Font) Kerning(i0, i1 Index) int16 {
- if f.nKern == 0 {
- return 0
- }
- g := uint32(i0)<<16 | uint32(i1)
- lo, hi := 0, f.nKern
- for lo < hi {
- i := (lo + hi) / 2
- d := data(f.kern[18+6*i:])
- ig := d.u32()
- if ig < g {
- lo = i + 1
- } else if ig > g {
- hi = i
- } else {
- return int16(d.u16())
- }
- }
- return 0
-}
-
-// Parse returns a new Font for the given TTF or TTC data.
-//
-// For TrueType Collections, the first font in the collection is parsed.
-func Parse(ttf []byte) (font *Font, err error) {
- return parse(ttf, 0)
-}
-
-func parse(ttf []byte, offset int) (font *Font, err error) {
- if len(ttf)-offset < 12 {
- err = FormatError("TTF data is too short")
- return
- }
- d := data(ttf[offset:])
- switch d.u32() {
- case 0x00010000:
- // No-op.
- case 0x74746366: // "ttcf" as a big-endian uint32.
- if offset != 0 {
- err = FormatError("recursive TTC")
- return
- }
- if d.u32() != 0x00010000 {
- // TODO: support TTC version 2.0, once I have such a .ttc file to test with.
- err = FormatError("bad TTC version")
- return
- }
- numFonts := int(d.u32())
- if numFonts <= 0 {
- err = FormatError("bad number of TTC fonts")
- return
- }
- if len(d)/4 < numFonts {
- err = FormatError("TTC offset table is too short")
- return
- }
- // TODO: provide an API to select which font in a TrueType collection to return,
- // not just the first one. This may require an API to parse a TTC's name tables,
- // so users of this package can select the font in a TTC by name.
- offset := int(d.u32())
- if offset <= 0 || offset > len(ttf) {
- err = FormatError("bad TTC offset")
- return
- }
- return parse(ttf, offset)
- default:
- err = FormatError("bad TTF version")
- return
- }
- n := int(d.u16())
- if len(ttf) < 16*n+12 {
- err = FormatError("TTF data is too short")
- return
- }
- f := new(Font)
- // Assign the table slices.
- for i := 0; i < n; i++ {
- x := 16*i + 12
- switch string(ttf[x : x+4]) {
- case "cmap":
- f.cmap, err = readTable(ttf, ttf[x+8:x+16])
- case "glyf":
- f.glyf, err = readTable(ttf, ttf[x+8:x+16])
- case "head":
- f.head, err = readTable(ttf, ttf[x+8:x+16])
- case "hhea":
- f.hhea, err = readTable(ttf, ttf[x+8:x+16])
- case "hmtx":
- f.hmtx, err = readTable(ttf, ttf[x+8:x+16])
- case "kern":
- f.kern, err = readTable(ttf, ttf[x+8:x+16])
- case "loca":
- f.loca, err = readTable(ttf, ttf[x+8:x+16])
- case "maxp":
- f.maxp, err = readTable(ttf, ttf[x+8:x+16])
- }
- if err != nil {
- return
- }
- }
- // Parse and sanity-check the TTF data.
- if err = f.parseHead(); err != nil {
- return
- }
- if err = f.parseMaxp(); err != nil {
- return
- }
- if err = f.parseCmap(); err != nil {
- return
- }
- if err = f.parseKern(); err != nil {
- return
- }
- if err = f.parseHhea(); err != nil {
- return
- }
- font = f
- return
-}
-
// A Point is a co-ordinate pair plus whether it is ``on'' a contour or an
// ``off'' control point.
type Point struct {
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