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font/sfnt: support fonts with "true" apple version tag

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OpenType specification mentions that fonts might contain Apple
version tag that is equal to "true" (see note in [1]). Currently,
the library returns a parsing error for those fonts.

CL adds Apple this version tag to the validation code and allows
fonts to omit OS/2 table, as mentioned in the TrueType spec [2].

[1] https://docs.microsoft.com/en-us/typography/opentype/spec/otff#organization-of-an-opentype-font

[2] https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6OS2.html

Change-Id: I13406fe97b091f24aaabf9b477df9c8fc8df883c
Reviewed-on: https://go-review.googlesource.com/c/146078
Reviewed-by: Nigel Tao <nigeltao@golang.org>
This commit is contained in:
Denys Smirnov 2018-10-30 23:05:30 +02:00 committed by Nigel Tao
parent d9c2484c48
commit dd492a22e4
1 changed files with 19 additions and 13 deletions
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32
font/sfnt/sfnt.go
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@ -333,7 +333,7 @@ func (c *Collection) initialize() error {
return errInvalidFontCollection
case dfontResourceDataOffset:
return c.parseDfont(buf, u32(buf[4:]), u32(buf[12:]))
case 0x00010000, 0x4f54544f:
case 0x00010000, 0x4f54544f, 0x74727565: // 0x10000, "OTTO", "true"
// Try parsing it as a single font instead of a collection.
c.offsets = []uint32{0}
case 0x74746366: // "ttcf".
@ -637,7 +637,7 @@ func (f *Font) initialize(offset int, isDfont bool) error {
if err != nil {
return err
}
buf, os2Vers, xHeight, capHeight, err := f.parseOS2(buf)
buf, hasXHeightCapHeight, xHeight, capHeight, err := f.parseOS2(buf)
if err != nil {
return err
}
@ -664,7 +664,7 @@ func (f *Font) initialize(offset int, isDfont bool) error {
f.cached.unitsPerEm = unitsPerEm
f.cached.xHeight = xHeight
if os2Vers <= 1 {
if !hasXHeightCapHeight {
xh, ch, err := f.initOS2Version1()
if err != nil {
return err
@ -695,6 +695,8 @@ func (f *Font) initializeTables(offset int, isDfont bool) (buf1 []byte, isPostSc
// No-op.
case 0x4f54544f: // "OTTO".
isPostScript = true
case 0x74727565: // "true"
// No-op.
case 0x74746366: // "ttcf".
return nil, false, errInvalidSingleFont
}
@ -1121,36 +1123,40 @@ func (f *Font) initOS2Version1() (xHeight, capHeight int32, err error) {
return int32(xh), int32(ch), nil
}
func (f *Font) parseOS2(buf []byte) (buf1 []byte, version uint16, xHeight, capHeight int32, err error) {
func (f *Font) parseOS2(buf []byte) (buf1 []byte, hasXHeightCapHeight bool, xHeight, capHeight int32, err error) {
// https://docs.microsoft.com/da-dk/typography/opentype/spec/os2
if f.os2.length < 2 {
return nil, 0, 0, 0, errInvalidOS2Table
if f.os2.length == 0 {
// Apple TrueType fonts might omit the OS/2 table.
return buf, false, 0, 0, nil
} else if f.os2.length < 2 {
return nil, false, 0, 0, errInvalidOS2Table
}
vers, err := f.src.u16(buf, f.os2, 0)
if err != nil {
return nil, 0, 0, 0, err
return nil, false, 0, 0, err
}
if vers <= 1 {
const headerSize = 86
if f.os2.length < headerSize {
return nil, 0, 0, 0, errInvalidOS2Table
return nil, false, 0, 0, errInvalidOS2Table
}
// Will resolve xHeight and capHeight later, see initOS2Version1.
return buf, vers, 0, 0, nil
return buf, false, 0, 0, nil
}
const headerSize = 96
if f.os2.length < headerSize {
return nil, 0, 0, 0, errInvalidOS2Table
return nil, false, 0, 0, errInvalidOS2Table
}
xh, err := f.src.u16(buf, f.os2, 86)
if err != nil {
return nil, 0, 0, 0, err
return nil, false, 0, 0, err
}
ch, err := f.src.u16(buf, f.os2, 88)
if err != nil {
return nil, 0, 0, 0, err
return nil, false, 0, 0, err
}
return buf, vers, int32(int16(xh)), int32(int16(ch)), nil
return buf, true, int32(int16(xh)), int32(int16(ch)), nil
}
// PostTable represents an information stored in the PostScript font section.