font/sfnt: don't reject multiple kern subtables.

A future commit will actually use subtables past the first one, but for
now, ignore them instead of failing on their presence.

Also add tests for the DejaVu proprietary fonts. Prior to this commit,
DejaVuSans-ExtraLight.ttf was unsupported.

Change-Id: Ic78a59c5ab30e4091efa2a04b89b12cb786157db
Reviewed-on: https://go-review.googlesource.com/42192
Reviewed-by: David Crawshaw <crawshaw@golang.org>

font/sfnt/proprietary_test.go

@@ -19,7 +19,11 @@ End User License Agreement (EULA) and a CAB format decoder. These tests assume
 that such fonts have already been installed. You may need to specify the
 directories for these fonts:
 
-go test golang.org/x/image/font/sfnt -args -proprietary -adobeDir=$HOME/fonts/adobe -appleDir=$HOME/fonts/apple -microsoftDir=$HOME/fonts/microsoft
+go test golang.org/x/image/font/sfnt -args -proprietary \
+	-adobeDir=$HOME/fonts/adobe \
+	-appleDir=$HOME/fonts/apple \
+	-dejavuDir=$HOME/fonts/dejavu \
+	-microsoftDir=$HOME/fonts/microsoft
 
 To only run those tests for the Microsoft fonts:
 
@@ -72,6 +76,13 @@ var (
 		"directory name for the Apple proprietary fonts",
 	)
 
+	dejavuDir = flag.String(
+		"dejavuDir",
+		// Get the fonts from https://dejavu-fonts.github.io/
+		"",
+		"directory name for the DejaVu proprietary fonts",
+	)
+
 	microsoftDir = flag.String(
 		"microsoftDir",
 		"/usr/share/fonts/truetype/msttcorefonts",
@@ -143,6 +154,18 @@ func TestProprietaryAppleHiragino1(t *testing.T) {
 	testProprietary(t, "apple", "ヒラギノ角ゴシック W0.ttc?1", 9000, -1)
 }
 
+func TestProprietaryDejaVuSansExtraLight(t *testing.T) {
+	testProprietary(t, "dejavu", "DejaVuSans-ExtraLight.ttf", 2000, -1)
+}
+
+func TestProprietaryDejaVuSansMono(t *testing.T) {
+	testProprietary(t, "dejavu", "DejaVuSansMono.ttf", 3300, -1)
+}
+
+func TestProprietaryDejaVuSerif(t *testing.T) {
+	testProprietary(t, "dejavu", "DejaVuSerif.ttf", 3500, -1)
+}
+
 func TestProprietaryMicrosoftArial(t *testing.T) {
 	testProprietary(t, "microsoft", "Arial.ttf", 1200, -1)
 }
@@ -192,6 +215,8 @@ func testProprietary(t *testing.T, proprietor, filename string, minNumGlyphs, fi
 		dir = *adobeDir
 	case "apple":
 		dir = *appleDir
+	case "dejavu":
+		dir = *dejavuDir
 	case "microsoft":
 		dir = *microsoftDir
 	default:
@@ -375,6 +400,10 @@ var proprietaryVersions = map[string]string{
 	"apple/ヒラギノ角ゴシック W0.ttc?0": "11.0d7e1",
 	"apple/ヒラギノ角ゴシック W0.ttc?1": "11.0d7e1",
 
+	"dejavu/DejaVuSans-ExtraLight.ttf": "Version 2.37",
+	"dejavu/DejaVuSansMono.ttf":        "Version 2.37",
+	"dejavu/DejaVuSerif.ttf":           "Version 2.37",
+
 	"microsoft/Arial.ttf":           "Version 2.82",
 	"microsoft/Arial.ttf?0":         "Version 2.82",
 	"microsoft/Comic_Sans_MS.ttf":   "Version 2.10",
@@ -403,6 +432,10 @@ var proprietaryFullNames = map[string]string{
 	"apple/ヒラギノ角ゴシック W0.ttc?0": "Hiragino Sans W0",
 	"apple/ヒラギノ角ゴシック W0.ttc?1": ".Hiragino Kaku Gothic Interface W0",
 
+	"dejavu/DejaVuSans-ExtraLight.ttf": "DejaVu Sans ExtraLight",
+	"dejavu/DejaVuSansMono.ttf":        "DejaVu Sans Mono",
+	"dejavu/DejaVuSerif.ttf":           "DejaVu Serif",
+
 	"microsoft/Arial.ttf":           "Arial",
 	"microsoft/Arial.ttf?0":         "Arial",
 	"microsoft/Comic_Sans_MS.ttf":   "Comic Sans MS",
@@ -469,6 +502,11 @@ var proprietaryGlyphIndexTestCases = map[string]map[rune]GlyphIndex{
 		'\U0001f100': 0,    // U+0001F100 DIGIT ZERO FULL STOP
 	},
 
+	"dejavu/DejaVuSerif.ttf": {
+		'\u0041': 36,   // U+0041 LATIN CAPITAL LETTER A
+		'\u1e00': 1418, // U+1E00 LATIN CAPITAL LETTER A WITH RING BELOW
+	},
+
 	"microsoft/Arial.ttf": {
 		'\u0041':     36,   // U+0041 LATIN CAPITAL LETTER A
 		'\u00f1':     120,  // U+00F1 LATIN SMALL LETTER N WITH TILDE
@@ -930,6 +968,23 @@ var proprietaryGlyphTestCases = map[string]map[rune][]Segment{
 		},
 	},
 
+	"dejavu/DejaVuSans-ExtraLight.ttf": {
+		'i': {
+			// - contour #0
+			moveTo(230, 1120),
+			lineTo(322, 1120),
+			lineTo(322, 0),
+			lineTo(230, 0),
+			lineTo(230, 1120),
+			// - contour #1
+			moveTo(230, 1556),
+			lineTo(322, 1556),
+			lineTo(322, 1430),
+			lineTo(230, 1430),
+			lineTo(230, 1556),
+		},
+	},
+
 	"microsoft/Arial.ttf": {
 		',': {
 			// - contour #0
@@ -1109,6 +1164,18 @@ type kernTestCase struct {
 // proprietaryKernTestCases hold a sample of each font's kerning pairs. The
 // numerical values can be verified by running the ttx tool.
 var proprietaryKernTestCases = map[string][]kernTestCase{
+	"dejavu/DejaVuSans-ExtraLight.ttf": {
+		{2048, font.HintingNone, [2]rune{'A', 'A'}, 57},
+		{2048, font.HintingNone, [2]rune{'W', 'A'}, -112},
+		// U+00C1 LATIN CAPITAL LETTER A WITH ACUTE
+		// U+01FA LATIN CAPITAL LETTER A WITH RING ABOVE AND ACUTE
+		// U+1E82 LATIN CAPITAL LETTER W WITH ACUTE
+		{2048, font.HintingNone, [2]rune{'\u00c1', 'A'}, 57},
+		// TODO: enable these next two test cases, when we support multiple
+		// kern subtables.
+		// {2048, font.HintingNone, [2]rune{'\u01fa', 'A'}, 57},
+		// {2048, font.HintingNone, [2]rune{'\u1e82', 'A'}, -112},
+	},
 	"microsoft/Arial.ttf": {
 		{2048, font.HintingNone, [2]rune{'A', 'V'}, -152},
 		// U+03B8 GREEK SMALL LETTER THETA

font/sfnt/sfnt.go

@@ -869,9 +869,11 @@ func (f *Font) parseKern(buf []byte) (buf1 []byte, kernNumPairs, kernOffset int3
 
 	switch version := u16(buf); version {
 	case 0:
-		// TODO: support numTables != 1. Testing that requires finding such a font.
+		if numTables := int(u16(buf[2:])); numTables == 0 {
-		if numTables := int(u16(buf[2:])); numTables != 1 {
+			return buf, 0, 0, nil
-			return nil, 0, 0, errUnsupportedKernTable
+		} else if numTables > 1 {
+			// TODO: support multiple subtables. For now, fall through and use
+			// only the first one.
 		}
 		return f.parseKernVersion0(buf, offset, length)
 	case 1: