Add the genbasicfont program.

example/genbasicfont/main.go

+// Copyright 2016 The Freetype-Go Authors. All rights reserved.
+// Use of this source code is governed by your choice of either the
+// FreeType License or the GNU General Public License version 2 (or
+// any later version), both of which can be found in the LICENSE file.
+
+// +build example
+//
+// This build tag means that "go install github.com/golang/freetype/..."
+// doesn't install this example program. Use "go run main.go" to run it or "go
+// install -tags=example" to install it.
+
+// Program genbasicfont generates Go source code that imports
+// golang.org/x/image/font/basicfont to provide a fixed width font face.
+package main
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"go/format"
+	"image"
+	"image/draw"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"strings"
+	"unicode"
+
+	"github.com/golang/freetype/truetype"
+	"golang.org/x/image/font"
+	"golang.org/x/image/math/fixed"
+)
+
+var (
+	fontfile = flag.String("fontfile", "../../testdata/luxisr.ttf", "filename or URL of the TTF font")
+	hinting  = flag.String("hinting", "none", "none, vertical or full")
+	pkg      = flag.String("pkg", "example", "the package name for the generated code")
+	size     = flag.Float64("size", 12, "the number of pixels in 1 em")
+	vr       = flag.String("var", "example", "the variable name for the generated code")
+)
+
+func loadFontFile() ([]byte, error) {
+	if strings.HasPrefix(*fontfile, "http://") || strings.HasPrefix(*fontfile, "https://") {
+		resp, err := http.Get(*fontfile)
+		if err != nil {
+			return nil, err
+		}
+		defer resp.Body.Close()
+		return ioutil.ReadAll(resp.Body)
+	}
+	return ioutil.ReadFile(*fontfile)
+}
+
+func parseHinting(h string) font.Hinting {
+	switch h {
+	case "full":
+		return font.HintingFull
+	case "vertical":
+		log.Fatal("TODO: have package truetype implement vertical hinting")
+		return font.HintingVertical
+	}
+	return font.HintingNone
+}
+
+func privateUseArea(r rune) bool {
+	return 0xe000 <= r && r <= 0xf8ff ||
+		0xf0000 <= r && r <= 0xffffd ||
+		0x100000 <= r && r <= 0x10fffd
+}
+
+func loadRanges(f *truetype.Font) (ret [][2]rune) {
+	rr := [2]rune{-1, -1}
+	for r := rune(0); r <= unicode.MaxRune; r++ {
+		if privateUseArea(r) {
+			continue
+		}
+		if f.Index(r) == 0 {
+			continue
+		}
+		if rr[1] == r {
+			rr[1] = r + 1
+			continue
+		}
+		if rr[0] != -1 {
+			ret = append(ret, rr)
+		}
+		rr = [2]rune{r, r + 1}
+	}
+	if rr[0] != -1 {
+		ret = append(ret, rr)
+	}
+	return ret
+}
+
+func emptyCol(m *image.Gray, r image.Rectangle, x int) bool {
+	for y := r.Min.Y; y < r.Max.Y; y++ {
+		if m.GrayAt(x, y).Y > 0 {
+			return false
+		}
+	}
+	return true
+}
+
+func emptyRow(m *image.Gray, r image.Rectangle, y int) bool {
+	for x := r.Min.X; x < r.Max.X; x++ {
+		if m.GrayAt(x, y).Y > 0 {
+			return false
+		}
+	}
+	return true
+}
+
+func tightBounds(m *image.Gray) (r image.Rectangle) {
+	r = m.Bounds()
+	for ; r.Min.Y < r.Max.Y && emptyRow(m, r, r.Min.Y+0); r.Min.Y++ {
+	}
+	for ; r.Min.Y < r.Max.Y && emptyRow(m, r, r.Max.Y-1); r.Max.Y-- {
+	}
+	for ; r.Min.X < r.Max.X && emptyCol(m, r, r.Min.X+0); r.Min.X++ {
+	}
+	for ; r.Min.X < r.Max.X && emptyCol(m, r, r.Max.X-1); r.Max.X-- {
+	}
+	return r
+}
+
+func printPix(ranges [][2]rune, glyphs map[rune]*image.Gray, b image.Rectangle) []byte {
+	buf := new(bytes.Buffer)
+	for _, rr := range ranges {
+		for r := rr[0]; r < rr[1]; r++ {
+			m := glyphs[r]
+			fmt.Fprintf(buf, "// U+%08x '%c'\n", r, r)
+			for y := b.Min.Y; y < b.Max.Y; y++ {
+				for x := b.Min.X; x < b.Max.X; x++ {
+					fmt.Fprintf(buf, "%#02x, ", m.GrayAt(x, y).Y)
+				}
+				fmt.Fprintln(buf)
+			}
+			fmt.Fprintln(buf)
+		}
+	}
+	return buf.Bytes()
+}
+
+func printRanges(ranges [][2]rune) []byte {
+	buf := new(bytes.Buffer)
+	offset := 0
+	for _, rr := range ranges {
+		fmt.Fprintf(buf, "{'\\U%08x', '\\U%08x', %d},\n", rr[0], rr[1], offset)
+		offset += int(rr[1] - rr[0])
+	}
+	return buf.Bytes()
+}
+
+func main() {
+	flag.Parse()
+	b, err := loadFontFile()
+	if err != nil {
+		log.Fatal(err)
+	}
+	f, err := truetype.Parse(b)
+	if err != nil {
+		log.Fatal(err)
+	}
+	face := truetype.NewFace(f, &truetype.Options{
+		Size:    *size,
+		Hinting: parseHinting(*hinting),
+	})
+	defer face.Close()
+
+	fBounds := f.Bounds(fixed.Int26_6(*size * 64))
+	iBounds := image.Rect(
+		+fBounds.Min.X.Floor(),
+		-fBounds.Max.Y.Ceil(),
+		+fBounds.Max.X.Ceil(),
+		-fBounds.Min.Y.Floor(),
+	)
+
+	tBounds := image.Rectangle{}
+	glyphs := map[rune]*image.Gray{}
+	advance := fixed.Int26_6(-1)
+
+	ranges := loadRanges(f)
+	for _, rr := range ranges {
+		for r := rr[0]; r < rr[1]; r++ {
+			dr, mask, maskp, adv, ok := face.Glyph(fixed.Point26_6{}, r)
+			if !ok {
+				log.Fatalf("could not load glyph for %U", r)
+			}
+			if advance < 0 {
+				advance = adv
+			} else if advance != adv {
+				log.Fatalf("advance was not constant: got %v and %v", advance, adv)
+			}
+			dst := image.NewGray(iBounds)
+			draw.DrawMask(dst, dr, image.White, image.Point{}, mask, maskp, draw.Src)
+			glyphs[r] = dst
+			tBounds = tBounds.Union(tightBounds(dst))
+		}
+	}
+
+	// height is the glyph image height, not the inter-line spacing.
+	width, height := tBounds.Dx(), tBounds.Dy()
+
+	buf := new(bytes.Buffer)
+	fmt.Fprintf(buf, "// generated by go generate; DO NOT EDIT.\n\npackage %s\n\n", *pkg)
+	fmt.Fprintf(buf, "import (\n\"image\"\n\n\"golang.org/x/image/font/basicfont\"\n)\n\n")
+	fmt.Fprintf(buf, "// %s contains %d %d×%d glyphs in %d Pix bytes.\n",
+		*vr, len(glyphs), width, height, len(glyphs)*width*height)
+	fmt.Fprintf(buf, `var %s = basicfont.Face{
+		Advance: %d,
+		Width:   %d,
+		Height:  %d,
+		Ascent:  %d,
+		Descent: %d,
+		Left: %d,
+		Mask: &image.Alpha{
+			Stride: %d,
+			Rect: image.Rectangle{Max: image.Point{%d, %d*%d}},
+			Pix: []byte{
+				%s
+			},
+		},
+		Ranges: []basicfont.Range{
+			%s
+		},
+	}`, *vr, advance.Ceil(), width, face.Metrics().Height.Ceil(), -tBounds.Min.Y, +tBounds.Max.Y, tBounds.Min.X,
+		width, width, len(glyphs), height,
+		printPix(ranges, glyphs, tBounds), printRanges(ranges))
+
+	fmted, err := format.Source(buf.Bytes())
+	if err != nil {
+		log.Fatalf("format.Source: %v", err)
+	}
+	if err := ioutil.WriteFile(*vr+".go", fmted, 0644); err != nil {
+		log.Fatalf("ioutil.WriteFile: %v", err)
+	}
+}