font/sfnt: support parsing legacy fonts with OS2 table version <= 1
Library assumes that OS/2 header size is at least 96 bytes,
which is not the case for fonts with OS/2 table version <= 1.
This CL adds a version test and handles the legacy header.
Fixes golang/go#28339
Change-Id: I79bd8f8bbf262c1caaf4e66888446159b5e4fb43
Reviewed-on: https://go-review.googlesource.com/c/144079
Reviewed-by: Nigel Tao <nigeltao@golang.org>
Reviewed-by: Elias Naur <elias.naur@gmail.com>
diff --git a/font/sfnt/sfnt.go b/font/sfnt/sfnt.go
index 0b46d0a..eaae675 100644
--- a/font/sfnt/sfnt.go
+++ b/font/sfnt/sfnt.go
@@ -637,7 +637,7 @@
if err != nil {
return err
}
- buf, xHeight, capHeight, err := f.parseOS2(buf)
+ buf, os2Vers, xHeight, capHeight, err := f.parseOS2(buf)
if err != nil {
return err
}
@@ -664,6 +664,15 @@
f.cached.unitsPerEm = unitsPerEm
f.cached.xHeight = xHeight
+ if os2Vers <= 1 {
+ xh, ch, err := f.initOS2Version1()
+ if err != nil {
+ return err
+ }
+ f.cached.xHeight = xh
+ f.cached.capHeight = ch
+ }
+
return nil
}
@@ -1065,22 +1074,80 @@
return buf, ret, isColorBitmap, nil
}
-func (f *Font) parseOS2(buf []byte) (buf1 []byte, xHeight, capHeight int32, err error) {
- // https://docs.microsoft.com/da-dk/typography/opentype/spec/os2
+func (f *Font) glyphTopOS2(b *Buffer, ppem fixed.Int26_6, r rune) (int32, error) {
+ ind, err := f.GlyphIndex(b, r)
+ if err != nil && err != ErrNotFound {
+ return 0, err
+ } else if ind == 0 {
+ return 0, nil
+ }
+ // Y axis points down
+ var min fixed.Int26_6
+ seg, err := f.LoadGlyph(b, ind, ppem, nil)
+ if err != nil {
+ return 0, err
+ }
+ for _, s := range seg {
+ for _, p := range s.Args {
+ if p.Y < min {
+ min = p.Y
+ }
+ }
+ }
+ return int32(min), nil
+}
+func (f *Font) initOS2Version1() (xHeight, capHeight int32, err error) {
+ ppem := fixed.Int26_6(f.UnitsPerEm())
+ var b Buffer
+
+ // sxHeight equal to the top of the unscaled and unhinted glyph bounding box
+ // of the glyph encoded at U+0078 (LATIN SMALL LETTER X).
+ xh, err := f.glyphTopOS2(&b, ppem, 'x')
+ if err != nil {
+ return 0, 0, err
+ }
+
+ // sCapHeight may be set equal to the top of the unscaled and unhinted glyph
+ // bounding box of the glyph encoded at U+0048 (LATIN CAPITAL LETTER H).
+ ch, err := f.glyphTopOS2(&b, ppem, 'H')
+ if err != nil {
+ return 0, 0, err
+ }
+
+ return int32(xh), int32(ch), nil
+}
+
+func (f *Font) parseOS2(buf []byte) (buf1 []byte, version uint16, 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
+ }
+ vers, err := f.src.u16(buf, f.os2, 0)
+ if err != nil {
+ return nil, 0, 0, 0, err
+ }
+ if vers <= 1 {
+ const headerSize = 86
+ if f.os2.length < headerSize {
+ return nil, 0, 0, 0, errInvalidOS2Table
+ }
+ // Will resolve xHeight and capHeight later, see initOS2Version1.
+ return buf, vers, 0, 0, nil
+ }
const headerSize = 96
if f.os2.length < headerSize {
- return nil, 0, 0, errInvalidOS2Table
+ return nil, 0, 0, 0, errInvalidOS2Table
}
xh, err := f.src.u16(buf, f.os2, 86)
if err != nil {
- return nil, 0, 0, err
+ return nil, 0, 0, 0, err
}
ch, err := f.src.u16(buf, f.os2, 88)
if err != nil {
- return nil, 0, 0, err
+ return nil, 0, 0, 0, err
}
- return buf, int32(int16(xh)), int32(int16(ch)), nil
+ return buf, vers, int32(int16(xh)), int32(int16(ch)), nil
}
func (f *Font) parsePost(buf []byte, numGlyphs int32) (buf1 []byte, postTableVersion uint32, err error) {
