mobile/font: access to system fonts

This initially supports reading two common system fonts. At some point
there should be a more general Open function, but first I need to work
out how to to turn font names into android file names.

Fixes golang/go#9419.

Change-Id: I8321df873315a5222c39dccf961f742f2e2a7a4c
Reviewed-on: https://go-review.googlesource.com/2059
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

app/debug/fps.go

@@ -9,14 +9,13 @@ import (
 	"fmt"
 	"image"
 	"image/draw"
-	"io/ioutil"
 	"log"
 	"math"
-	"runtime"
 	"sync"
 	"time"
 
 	"code.google.com/p/freetype-go/freetype"
+	"golang.org/x/mobile/font"
 	"golang.org/x/mobile/geom"
 	"golang.org/x/mobile/gl/glutil"
 )
@@ -34,22 +33,7 @@ var fps struct {
 // TODO(crawshaw): The gldebug mode needs to complain loudly when GL functions
 //                 are called before init, because often they fail silently.
 func fpsInit() {
-	font := ""
-	switch runtime.GOOS {
-	case "android":
-		font = "/system/fonts/DroidSansMono.ttf"
-	case "darwin":
-		font = "/Library/Fonts/Andale Mono.ttf"
-	case "linux":
-		font = "/usr/share/fonts/truetype/droid/DroidSansMono.ttf"
-	default:
-		panic(fmt.Sprintf("go.mobile/app/debug: unsupported runtime.GOOS %q", runtime.GOOS))
-	}
-
-	b, err := ioutil.ReadFile(font)
-	if err != nil {
-		panic(err)
-	}
+	b := font.Monospace()
 	f, err := freetype.ParseFont(b)
 	if err != nil {
 		panic(err)

font/font.go

@@ -0,0 +1,26 @@
+// Copyright 2014 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 font provides platform independent access to system fonts.
+package font
+
+// Default returns the default system font.
+// The font is encoded as a TTF.
+func Default() []byte {
+	b, err := buildDefault()
+	if err != nil {
+		panic(err)
+	}
+	return b
+}
+
+// Monospace returns the default system fixed-pitch font.
+// The font is encoded as a TTF.
+func Monospace() []byte {
+	b, err := buildMonospace()
+	if err != nil {
+		panic(err)
+	}
+	return b
+}

font/font_android.go

@@ -0,0 +1,15 @@
+// Copyright 2014 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 font
+
+import "io/ioutil"
+
+func buildDefault() ([]byte, error) {
+	return ioutil.ReadFile("/system/fonts/DroidSans.ttf")
+}
+
+func buildMonospace() ([]byte, error) {
+	return ioutil.ReadFile("/system/fonts/DroidSansMono.ttf")
+}

font/font_darwin.go

@@ -0,0 +1,76 @@
+// Copyright 2014 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 font
+
+/*
+#cgo darwin LDFLAGS: -framework CoreFoundation -framework CoreText
+#include <CoreFoundation/CFArray.h>
+#include <CoreFoundation/CFBase.h>
+#include <CoreFoundation/CFData.h>
+#include <CoreText/CTFont.h>
+*/
+import "C"
+import "unsafe"
+
+func buildFont(f C.CTFontRef) []byte {
+	ctags := C.CTFontCopyAvailableTables(f, C.kCTFontTableOptionExcludeSynthetic)
+	tagsCount := C.CFArrayGetCount(ctags)
+
+	var tags []uint32
+	var dataRefs []C.CFDataRef
+	var dataLens []uint32
+
+	for i := C.CFIndex(0); i < tagsCount; i++ {
+		tag := (C.CTFontTableTag)((uintptr)(C.CFArrayGetValueAtIndex(ctags, i)))
+		dataRef := C.CTFontCopyTable(f, tag, 0) // retained
+		tags = append(tags, uint32(tag))
+		dataRefs = append(dataRefs, dataRef)
+		dataLens = append(dataLens, uint32(C.CFDataGetLength(dataRef)))
+	}
+
+	totalLen := 0
+	for _, l := range dataLens {
+		totalLen += int(l)
+	}
+
+	// Big-endian output.
+	buf := make([]byte, 0, 12+16*len(tags)+totalLen)
+	write16 := func(x uint16) { buf = append(buf, byte(x>>8), byte(x)) }
+	write32 := func(x uint32) { buf = append(buf, byte(x>>24), byte(x>>16), byte(x>>8), byte(x)) }
+
+	// File format description: http://www.microsoft.com/typography/otspec/otff.htm
+	write32(0x00010000)        // version 1.0
+	write16(uint16(len(tags))) // numTables
+	write16(0)                 // searchRange
+	write16(0)                 // entrySelector
+	write16(0)                 // rangeShift
+
+	// Table tags, includes offsets into following data segments.
+	offset := uint32(12 + 16*len(tags)) // offset starts after table tags
+	for i, tag := range tags {
+		write32(tag)
+		write32(0)
+		write32(offset)
+		write32(dataLens[i])
+		offset += dataLens[i]
+	}
+
+	// Data segments.
+	for i, dataRef := range dataRefs {
+		data := (*[1<<31 - 2]byte)((unsafe.Pointer)(C.CFDataGetBytePtr(dataRef)))[:dataLens[i]]
+		buf = append(buf, data...)
+		C.CFRelease(C.CFTypeRef(dataRef))
+	}
+
+	return buf
+}
+
+func buildDefault() ([]byte, error) {
+	return buildFont(C.CTFontCreateUIFontForLanguage(C.kCTFontSystemFontType, 0, nil)), nil
+}
+
+func buildMonospace() ([]byte, error) {
+	return buildFont(C.CTFontCreateUIFontForLanguage(C.kCTFontUserFixedPitchFontType, 0, nil)), nil
+}

font/font_linux.go

@@ -0,0 +1,17 @@
+// Copyright 2014 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.
+
+// +build !android
+
+package font
+
+import "io/ioutil"
+
+func buildDefault() ([]byte, error) {
+	return ioutil.ReadFile("/usr/share/fonts/truetype/droid/DroidSans.ttf")
+}
+
+func buildMonospace() ([]byte, error) {
+	return ioutil.ReadFile("/usr/share/fonts/truetype/droid/DroidSansMono.ttf")
+}

font/font_test.go

@@ -0,0 +1,16 @@
+package font
+
+import (
+	"testing"
+
+	"code.google.com/p/freetype-go/freetype"
+)
+
+func TestLoadFonts(t *testing.T) {
+	if _, err := freetype.ParseFont(Default()); err != nil {
+		t.Fatalf("default font: %v", err)
+	}
+	if _, err := freetype.ParseFont(Monospace()); err != nil {
+		t.Fatalf("monospace font: %v", err)
+	}
+}