font/basicfont: new package for a basic font face.

The key feature is that its data is entirely self-contained and does not
require loading from separate files.

Change-Id: I4ef72b52cde93597be89dcfd55659f418c6cab23
Reviewed-on: https://go-review.googlesource.com/14486
Reviewed-by: Rob Pike <r@golang.org>

font/basicfont/basicfont.go

@@ -0,0 +1,113 @@
+// Copyright 2015 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.
+
+//go:generate go run gen.go
+
+// Package basicfont provides fixed-size font faces.
+package basicfont // import "golang.org/x/image/font/basicfont"
+
+import (
+	"image"
+
+	"golang.org/x/image/math/fixed"
+)
+
+// Range maps a contiguous range of runes to vertically adjacent sub-images of
+// a Face's Mask image. The rune range is inclusive on the low end and
+// exclusive on the high end.
+//
+// If Low <= r && r < High, then the rune r is mapped to the sub-image of
+// Face.Mask whose bounds are image.Rect(0, y, Face.Width, y+Face.Height),
+// where y equals (int(r-Low) + Offset) * Face.Height.
+type Range struct {
+	Low, High rune
+	Offset    int
+}
+
+// Face7x13 is a Face derived from the public domain X11 misc-fixed font files.
+//
+// At the moment, it holds the printable characters in ASCII starting with
+// space, and the Unicode replacement character U+FFFD.
+//
+// Its data is entirely self-contained and does not require loading from
+// separate files.
+var Face7x13 = &Face{
+	Advance: 7,
+	Width:   6,
+	Height:  13,
+	Ascent:  11,
+	Mask:    mask7x13,
+	Ranges: []Range{
+		{'\u0020', '\u007f', 0},
+		{'\ufffd', '\ufffe', 95},
+	},
+}
+
+// Face is a basic font face whose glyphs all have the same metrics.
+//
+// It is safe to use concurrently.
+type Face struct {
+	// Advance is the glyph advance, in pixels.
+	Advance int
+	// Width is the glyph width, in pixels.
+	Width int
+	// Height is the glyph height, in pixels.
+	Height int
+	// Ascent is the glyph ascent, in pixels.
+	Ascent int
+
+	// TODO: do we also need Top and Left fields?
+
+	// Mask contains all of the glyph masks. Its width is typically the Face's
+	// Width, and its height a multiple of the Face's Height.
+	Mask image.Image
+	// Ranges map runes to sub-images of Mask. The rune ranges must not
+	// overlap, and must be in increasing rune order.
+	Ranges []Range
+}
+
+func (f *Face) Close() error                   { return nil }
+func (f *Face) Kern(r0, r1 rune) fixed.Int26_6 { return 0 }
+
+func (f *Face) Glyph(dot fixed.Point26_6, r rune) (
+	dr image.Rectangle, mask image.Image, maskp image.Point, advance fixed.Int26_6, ok bool) {
+
+loop:
+	for _, rr := range [2]rune{r, '\ufffd'} {
+		for _, rng := range f.Ranges {
+			if rr < rng.Low || rng.High <= rr {
+				continue
+			}
+			maskp.Y = (int(rr-rng.Low) + rng.Offset) * f.Height
+			ok = true
+			break loop
+		}
+	}
+	if !ok {
+		return image.Rectangle{}, nil, image.Point{}, 0, false
+	}
+
+	minX := int(dot.X+32) >> 6
+	minY := int(dot.Y+32)>>6 - f.Ascent
+	dr = image.Rectangle{
+		Min: image.Point{
+			X: minX,
+			Y: minY,
+		},
+		Max: image.Point{
+			X: minX + f.Width,
+			Y: minY + f.Height,
+		},
+	}
+
+	return dr, f.Mask, maskp, fixed.I(f.Advance), true
+}
+
+func (f *Face) GlyphBounds(r rune) (bounds fixed.Rectangle26_6, advance fixed.Int26_6, ok bool) {
+	return fixed.R(0, -f.Ascent, f.Width, -f.Ascent+f.Height), fixed.I(f.Advance), true
+}
+
+func (f *Face) GlyphAdvance(r rune) (advance fixed.Int26_6, ok bool) {
+	return fixed.I(f.Advance), true
+}

font/basicfont/gen.go

@@ -0,0 +1,115 @@
+// Copyright 2015 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 ignore
+
+// This program generates data.go.
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"go/format"
+	"image"
+	"image/draw"
+	"io/ioutil"
+	"log"
+	"path"
+	"path/filepath"
+
+	"golang.org/x/image/font"
+	"golang.org/x/image/font/plan9font"
+	"golang.org/x/image/math/fixed"
+)
+
+func main() {
+	// nGlyphs is the number of glyphs to generate: 95 characters in the range
+	// [0x20, 0x7e], plus the replacement character.
+	const nGlyphs = 95 + 1
+	// The particular font (unicode.7x13.font) leaves the right-most column
+	// empty in its ASCII glyphs. We don't have to include that column in the
+	// generated glyphs, so we subtract one off the effective width.
+	const width, height, ascent = 7 - 1, 13, 11
+
+	readFile := func(name string) ([]byte, error) {
+		return ioutil.ReadFile(filepath.FromSlash(path.Join("../testdata/fixed", name)))
+	}
+	fontData, err := readFile("unicode.7x13.font")
+	if err != nil {
+		log.Fatalf("readFile: %v", err)
+	}
+	face, err := plan9font.ParseFont(fontData, readFile)
+	if err != nil {
+		log.Fatalf("plan9font.ParseFont: %v", err)
+	}
+
+	dst := image.NewRGBA(image.Rect(0, 0, width, nGlyphs*height))
+	draw.Draw(dst, dst.Bounds(), image.Black, image.Point{}, draw.Src)
+	d := &font.Drawer{
+		Dst:  dst,
+		Src:  image.White,
+		Face: face,
+	}
+	for i := 0; i < nGlyphs; i++ {
+		r := '\ufffd'
+		if i < nGlyphs-1 {
+			r = 0x20 + rune(i)
+		}
+		d.Dot = fixed.P(0, height*i+ascent)
+		d.DrawString(string(r))
+	}
+
+	w := bytes.NewBuffer(nil)
+	w.WriteString(preamble)
+	fmt.Fprintf(w, "// mask7x13 contains %d %d×%d glyphs in %d Pix bytes.\n", nGlyphs, width, height, nGlyphs*width*height)
+	fmt.Fprintf(w, "var mask7x13 = &image.Alpha{\n")
+	fmt.Fprintf(w, "  Stride: %d,\n", width)
+	fmt.Fprintf(w, "  Rect: image.Rectangle{Max: image.Point{%d, %d*%d}},\n", width, nGlyphs, height)
+	fmt.Fprintf(w, "  Pix: []byte{\n")
+	b := dst.Bounds()
+	for y := b.Min.Y; y < b.Max.Y; y++ {
+		if y%height == 0 {
+			if y != 0 {
+				w.WriteByte('\n')
+			}
+			i := y / height
+			if i < nGlyphs-1 {
+				i += 0x20
+				fmt.Fprintf(w, "// %#2x %q\n", i, rune(i))
+			} else {
+				fmt.Fprintf(w, "// U+FFFD REPLACEMENT CHARACTER\n")
+			}
+		}
+
+		for x := b.Min.X; x < b.Max.X; x++ {
+			if dst.RGBAAt(x, y).R > 0 {
+				w.WriteString("0xff,")
+			} else {
+				w.WriteString("0x00,")
+			}
+		}
+		w.WriteByte('\n')
+	}
+	w.WriteString("},\n}\n")
+
+	fmted, err := format.Source(w.Bytes())
+	if err != nil {
+		log.Fatalf("format.Source: %v", err)
+	}
+	if err := ioutil.WriteFile("data.go", fmted, 0644); err != nil {
+		log.Fatalf("ioutil.WriteFile: %v", err)
+	}
+}
+
+const preamble = `// generated by go generate; DO NOT EDIT.
+
+package basicfont
+
+// This data is derived from files in the font/fixed directory of the Plan 9
+// Port source code (https://github.com/9fans/plan9port) which were originally
+// based on the public domain X11 misc-fixed font files.
+
+import "image"
+
+`