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freetype: support TrueType Collection files (.TTC files, as opposed to

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.TTF files)

R=bradfitz
CC=golang-dev
http://codereview.appspot.com/6194050
This commit is contained in:
Nigel Tao 2012-05-07 11:42:35 +10:00
parent 9a8fb30c20
commit eaa4846c62
1 changed files with 45 additions and 8 deletions
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53
freetype/truetype/truetype.go
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@ -3,9 +3,9 @@
// 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 file format. That format
// is documented at http://developer.apple.com/fonts/TTRefMan/ and
// http://www.microsoft.com/typography/otspec/
// 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
@ -350,15 +350,52 @@ func (f *Font) Kerning(i0, i1 Index) int16 {
return 0
}
// Parse returns a new Font for the given TTF data.
// 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) {
if len(ttf) < 12 {
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[0:])
if d.u32() != 0x00010000 {
err = FormatError("bad version")
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())