font/sfnt: support early version 0 OS/2 tables
Version 0 OS/2 tables can be as small as 68 bytes.
See https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6OS2.html.
This works is taken over from https://go.dev/cl/510055 by Erik Agsjö.
Fixes golang/go#41658
Change-Id: If6fb961943b5563ed21fe5148252005743c17168
Reviewed-on: https://go-review.googlesource.com/c/image/+/533495
Run-TryBot: Hajime Hoshi <hajimehoshi@gmail.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Nigel Tao <nigeltao@golang.org>
Reviewed-by: Nigel Tao (INACTIVE; USE @golang.org INSTEAD) <nigeltao@google.com>
diff --git a/font/sfnt/sfnt.go b/font/sfnt/sfnt.go
index 8d0dba7..8ed19e2 100644
--- a/font/sfnt/sfnt.go
+++ b/font/sfnt/sfnt.go
@@ -745,7 +745,7 @@
f.cached.xHeight = xHeight
if !hasXHeightCapHeight {
- xh, ch, err := f.initOS2Version1()
+ xh, ch, err := f.initOS2VersionBelow2()
if err != nil {
return err
}
@@ -1201,7 +1201,7 @@
return int32(min), nil
}
-func (f *Font) initOS2Version1() (xHeight, capHeight int32, err error) {
+func (f *Font) initOS2VersionBelow2() (xHeight, capHeight int32, err error) {
ppem := fixed.Int26_6(f.UnitsPerEm())
var b Buffer
@@ -1235,12 +1235,14 @@
if err != nil {
return nil, false, 0, 0, err
}
- if vers <= 1 {
- const headerSize = 86
+ if vers < 2 {
+ // "The original TrueType specification had this table at 68 bytes long."
+ // https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6OS2.html
+ const headerSize = 68
if f.os2.length < headerSize {
return nil, false, 0, 0, errInvalidOS2Table
}
- // Will resolve xHeight and capHeight later, see initOS2Version1.
+ // Will resolve xHeight and capHeight later, see initOS2VersionBelow2.
return buf, false, 0, 0, nil
}
const headerSize = 96
