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// Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package sfnt
import (
"golang.org/x/text/encoding/charmap"
)
// Platform IDs and Platform Specific IDs as per
// https://www.microsoft.com/typography/otspec/name.htm
const (
pidUnicode = 0
pidMacintosh = 1
pidWindows = 3
psidUnicode2BMPOnly = 3
psidUnicode2FullRepertoire = 4
// Note that FontForge may generate a bogus Platform Specific ID (value 10)
// for the Unicode Platform ID (value 0). See
// https://github.com/fontforge/fontforge/issues/2728
psidMacintoshRoman = 0
psidWindowsSymbol = 0
psidWindowsUCS2 = 1
psidWindowsUCS4 = 10
)
// platformEncodingWidth returns the number of bytes per character assumed by
// the given Platform ID and Platform Specific ID.
//
// Very old fonts, from before Unicode was widely adopted, assume only 1 byte
// per character: a character map.
//
// Old fonts, from when Unicode meant the Basic Multilingual Plane (BMP),
// assume that 2 bytes per character is sufficient.
//
// Recent fonts naturally support the full range of Unicode code points, which
// can take up to 4 bytes per character. Such fonts might still choose one of
// the legacy encodings if e.g. their repertoire is limited to the BMP, for
// greater compatibility with older software, or because the resultant file
// size can be smaller.
func platformEncodingWidth(pid, psid uint16) int {
switch pid {
case pidUnicode:
switch psid {
case psidUnicode2BMPOnly:
return 2
case psidUnicode2FullRepertoire:
return 4
}
case pidMacintosh:
switch psid {
case psidMacintoshRoman:
return 1
}
case pidWindows:
switch psid {
case psidWindowsSymbol:
return 2
case psidWindowsUCS2:
return 2
case psidWindowsUCS4:
return 4
}
}
return 0
}
// The various cmap formats are described at
// https://www.microsoft.com/typography/otspec/cmap.htm
var supportedCmapFormat = func(format, pid, psid uint16) bool {
switch format {
case 0:
return pid == pidMacintosh && psid == psidMacintoshRoman
case 4:
return true
case 12:
return true
}
return false
}
func (f *Font) makeCachedGlyphIndex(buf []byte, offset, length uint32, format uint16) ([]byte, glyphIndexFunc, error) {
switch format {
case 0:
return f.makeCachedGlyphIndexFormat0(buf, offset, length)
case 4:
return f.makeCachedGlyphIndexFormat4(buf, offset, length)
case 12:
return f.makeCachedGlyphIndexFormat12(buf, offset, length)
}
panic("unreachable")
}
func (f *Font) makeCachedGlyphIndexFormat0(buf []byte, offset, length uint32) ([]byte, glyphIndexFunc, error) {
if length != 6+256 || offset+length > f.cmap.length {
return nil, nil, errInvalidCmapTable
}
var err error
buf, err = f.src.view(buf, int(f.cmap.offset+offset), int(length))
if err != nil {
return nil, nil, err
}
var table [256]byte
copy(table[:], buf[6:])
return buf, func(f *Font, b *Buffer, r rune) (GlyphIndex, error) {
x, ok := charmap.Macintosh.EncodeRune(r)
if !ok {
// The source rune r is not representable in the Macintosh-Roman encoding.
return 0, nil
}
return GlyphIndex(table[x]), nil
}, nil
}
func (f *Font) makeCachedGlyphIndexFormat4(buf []byte, offset, length uint32) ([]byte, glyphIndexFunc, error) {
const headerSize = 14
if offset+headerSize > f.cmap.length {
return nil, nil, errInvalidCmapTable
}
var err error
buf, err = f.src.view(buf, int(f.cmap.offset+offset), headerSize)
if err != nil {
return nil, nil, err
}
offset += headerSize
segCount := u16(buf[6:])
if segCount&1 != 0 {
return nil, nil, errInvalidCmapTable
}
segCount /= 2
if segCount > maxCmapSegments {
return nil, nil, errUnsupportedNumberOfCmapSegments
}
eLength := 8*uint32(segCount) + 2
if offset+eLength > f.cmap.length {
return nil, nil, errInvalidCmapTable
}
buf, err = f.src.view(buf, int(f.cmap.offset+offset), int(eLength))
if err != nil {
return nil, nil, err
}
offset += eLength
entries := make([]cmapEntry16, segCount)
for i := range entries {
entries[i] = cmapEntry16{
end: u16(buf[0*len(entries)+0+2*i:]),
start: u16(buf[2*len(entries)+2+2*i:]),
delta: u16(buf[4*len(entries)+2+2*i:]),
offset: u16(buf[6*len(entries)+2+2*i:]),
}
}
indexesBase := f.cmap.offset + offset
indexesLength := f.cmap.length - offset
return buf, func(f *Font, b *Buffer, r rune) (GlyphIndex, error) {
if uint32(r) > 0xffff {
return 0, nil
}
c := uint16(r)
for i, j := 0, len(entries); i < j; {
h := i + (j-i)/2
entry := &entries[h]
if c < entry.start {
j = h
} else if entry.end < c {
i = h + 1
} else if entry.offset == 0 {
return GlyphIndex(c + entry.delta), nil
} else {
offset := uint32(entry.offset) + 2*uint32(h-len(entries)+int(c-entry.start))
if offset > indexesLength || offset+2 > indexesLength {
return 0, errInvalidCmapTable
}
x, err := b.view(&f.src, int(indexesBase+offset), 2)
if err != nil {
return 0, err
}
return GlyphIndex(u16(x)), nil
}
}
return 0, nil
}, nil
}
func (f *Font) makeCachedGlyphIndexFormat12(buf []byte, offset, _ uint32) ([]byte, glyphIndexFunc, error) {
const headerSize = 16
if offset+headerSize > f.cmap.length {
return nil, nil, errInvalidCmapTable
}
var err error
buf, err = f.src.view(buf, int(f.cmap.offset+offset), headerSize)
if err != nil {
return nil, nil, err
}
length := u32(buf[4:])
if f.cmap.length < offset || length > f.cmap.length-offset {
return nil, nil, errInvalidCmapTable
}
offset += headerSize
numGroups := u32(buf[12:])
if numGroups > maxCmapSegments {
return nil, nil, errUnsupportedNumberOfCmapSegments
}
eLength := 12 * numGroups
if headerSize+eLength != length {
return nil, nil, errInvalidCmapTable
}
buf, err = f.src.view(buf, int(f.cmap.offset+offset), int(eLength))
if err != nil {
return nil, nil, err
}
offset += eLength
entries := make([]cmapEntry32, numGroups)
for i := range entries {
entries[i] = cmapEntry32{
start: u32(buf[0+12*i:]),
end: u32(buf[4+12*i:]),
delta: u32(buf[8+12*i:]),
}
}
return buf, func(f *Font, b *Buffer, r rune) (GlyphIndex, error) {
c := uint32(r)
for i, j := 0, len(entries); i < j; {
h := i + (j-i)/2
entry := &entries[h]
if c < entry.start {
j = h
} else if entry.end < c {
i = h + 1
} else {
return GlyphIndex(c - entry.start + entry.delta), nil
}
}
return 0, nil
}, nil
}
type cmapEntry16 struct {
end, start, delta, offset uint16
}
type cmapEntry32 struct {
start, end, delta uint32
}
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