1 files changed, 353 insertions, 0 deletions
diff --git a/bdf/bdf.go b/bdf/bdf.go
new file mode 100644
index 0000000..c02e31e
--- /dev/null
+++ b/bdf/bdf.go
@@ -0,0 +1,353 @@
+package bdf
+
+import (
+	"bufio"
+	"encoding/hex"
+	"fmt"
+	"image"
+	"image/color"
+	"image/draw"
+	"io"
+	"strconv"
+)
+
+// glyph is a singular bitmap glyph to be used as a mask, assumed to directly
+// correspond to a rune. A zero value is also valid and drawable.
+type glyph struct {
+	// Coordinates are relative to the origin, on the baseline.
+	// The ascent is thus negative, unlike the usual model.
+	bounds  image.Rectangle
+	bitmap  []byte
+	advance int
+}
+
+// ColorModel implements image.Image.
+func (g *glyph) ColorModel() color.Model { return color.Alpha16Model }
+
+// Bounds implements image.Image.
+func (g *glyph) Bounds() image.Rectangle { return g.bounds }
+
+// At implements image.Image. This is going to be somewhat slow.
+func (g *glyph) At(x, y int) color.Color {
+	x -= g.bounds.Min.X
+	y -= g.bounds.Min.Y
+
+	dx, dy := g.bounds.Dx(), g.bounds.Dy()
+	if x < 0 || y < 0 || x >= dx || y >= dy {
+		return color.Transparent
+	}
+
+	stride, offset, bit := (dx+7)/8, x/8, byte(1<<uint(7-x%8))
+	if g.bitmap[y*stride+offset]&bit == 0 {
+		return color.Transparent
+	}
+	return color.Opaque
+}
+
+// -----------------------------------------------------------------------------
+
+// Font represents a particular bitmap font.
+type Font struct {
+	Name     string
+	glyphs   map[rune]glyph
+	fallback glyph
+}
+
+// FindGlyph returns the best glyph to use for the given rune.
+// The returned boolean indicates whether a fallback has been used.
+func (f *Font) FindGlyph(r rune) (glyph, bool) {
+	if g, ok := f.glyphs[r]; ok {
+		return g, true
+	}
+	return f.fallback, false
+}
+
+// DrawString draws the specified text string onto dst horizontally along
+// the baseline starting at dp, using black color.
+func (f *Font) DrawString(dst draw.Image, dp image.Point, s string) {
+	for _, r := range s {
+		g, _ := f.FindGlyph(r)
+		draw.DrawMask(dst, g.bounds.Add(dp),
+			image.Black, image.ZP, &g, g.bounds.Min, draw.Over)
+		dp.X += g.advance
+	}
+}
+
+// BoundString measures the text's bounds when drawn along the X axis
+// for the baseline. Also returns the total advance.
+func (f *Font) BoundString(s string) (image.Rectangle, int) {
+	var (
+		bounds image.Rectangle
+		dot    image.Point
+	)
+	for _, r := range s {
+		g, _ := f.FindGlyph(r)
+		bounds = bounds.Union(g.bounds.Add(dot))
+		dot.X += g.advance
+	}
+	return bounds, dot.X
+}
+
+// -----------------------------------------------------------------------------
+
+func latin1ToUTF8(latin1 []byte) string {
+	buf := make([]rune, len(latin1))
+	for i, b := range latin1 {
+		buf[i] = rune(b)
+	}
+	return string(buf)
+}
+
+// tokenize splits a BDF line into tokens. Quoted strings may start anywhere
+// on the line. We only enforce that they must end somewhere.
+func tokenize(s string) (tokens []string, err error) {
+	token, quotes, escape := []rune{}, false, false
+	for _, r := range s {
+		switch {
+		case escape:
+			switch r {
+			case '"':
+				escape = false
+				token = append(token, r)
+			case ' ', '\t':
+				quotes, escape = false, false
+				tokens = append(tokens, string(token))
+				token = nil
+			default:
+				quotes, escape = false, false
+				token = append(token, r)
+			}
+		case quotes:
+			switch r {
+			case '"':
+				escape = true
+			default:
+				token = append(token, r)
+			}
+		default:
+			switch r {
+			case '"':
+				// We could also enable quote processing on demand,
+				// so that it is only turned on in properties.
+				if len(tokens) < 1 || tokens[0] != "COMMENT" {
+					quotes = true
+				} else {
+					token = append(token, r)
+				}
+			case ' ', '\t':
+				if len(token) > 0 {
+					tokens = append(tokens, string(token))
+					token = nil
+				}
+			default:
+				token = append(token, r)
+			}
+		}
+	}
+	if quotes && !escape {
+		return nil, fmt.Errorf("strings may not contain newlines")
+	}
+	if quotes || len(token) > 0 {
+		tokens = append(tokens, string(token))
+	}
+	return tokens, nil
+}
+
+// -----------------------------------------------------------------------------
+
+// bdfParser is a basic and rather lenient parser of
+// Bitmap Distribution Format (BDF) files.
+type bdfParser struct {
+	scanner *bufio.Scanner // input reader
+	line    int            // current line number
+	tokens  []string       // tokens on the current line
+	font    *Font          // glyph storage
+
+	defaultBounds  image.Rectangle
+	defaultAdvance int
+	defaultChar    int
+}
+
+// readLine reads the next line and splits it into tokens.
+// Panics on error, returns false if the end of file has been reached normally.
+func (p *bdfParser) readLine() bool {
+	p.line++
+	if !p.scanner.Scan() {
+		if err := p.scanner.Err(); err != nil {
+			panic(err)
+		}
+		p.line--
+		return false
+	}
+
+	var err error
+	if p.tokens, err = tokenize(latin1ToUTF8(p.scanner.Bytes())); err != nil {
+		panic(err)
+	}
+
+	// Eh, it would be nicer iteratively, this may overrun the stack.
+	if len(p.tokens) == 0 {
+		return p.readLine()
+	}
+	return true
+}
+
+func (p *bdfParser) readCharEncoding() int {
+	if len(p.tokens) < 2 {
+		panic("insufficient arguments")
+	}
+	if i, err := strconv.Atoi(p.tokens[1]); err != nil {
+		panic(err)
+	} else {
+		return i // Some fonts even use -1 for things outside the encoding.
+	}
+}
+
+func (p *bdfParser) parseProperties() {
+	// The wording in the specification suggests that the argument
+	// with the number of properties to follow isn't reliable.
+	for p.readLine() && p.tokens[0] != "ENDPROPERTIES" {
+		switch p.tokens[0] {
+		case "DEFAULT_CHAR":
+			p.defaultChar = p.readCharEncoding()
+		}
+	}
+}
+
+// XXX: Ignoring vertical advance since we only expect purely horizontal fonts.
+func (p *bdfParser) readDwidth() int {
+	if len(p.tokens) < 2 {
+		panic("insufficient arguments")
+	}
+	if i, err := strconv.Atoi(p.tokens[1]); err != nil {
+		panic(err)
+	} else {
+		return i
+	}
+}
+
+func (p *bdfParser) readBBX() image.Rectangle {
+	if len(p.tokens) < 5 {
+		panic("insufficient arguments")
+	}
+	w, e1 := strconv.Atoi(p.tokens[1])
+	h, e2 := strconv.Atoi(p.tokens[2])
+	x, e3 := strconv.Atoi(p.tokens[3])
+	y, e4 := strconv.Atoi(p.tokens[4])
+	if e1 != nil || e2 != nil || e3 != nil || e4 != nil {
+		panic("invalid arguments")
+	}
+	if w < 0 || h < 0 {
+		panic("bounding boxes may not have negative dimensions")
+	}
+	return image.Rectangle{
+		Min: image.Point{x, -(y + h)},
+		Max: image.Point{x + w, -y},
+	}
+}
+
+func (p *bdfParser) parseChar() {
+	g := glyph{bounds: p.defaultBounds, advance: p.defaultAdvance}
+	bitmap, rows, encoding := false, 0, -1
+	for p.readLine() && p.tokens[0] != "ENDCHAR" {
+		if bitmap {
+			b, err := hex.DecodeString(p.tokens[0])
+			if err != nil {
+				panic(err)
+			}
+			if len(b) != (g.bounds.Dx()+7)/8 {
+				panic("invalid bitmap data, width mismatch")
+			}
+			g.bitmap = append(g.bitmap, b...)
+			rows++
+		} else {
+			switch p.tokens[0] {
+			case "ENCODING":
+				encoding = p.readCharEncoding()
+			case "DWIDTH":
+				g.advance = p.readDwidth()
+			case "BBX":
+				g.bounds = p.readBBX()
+			case "BITMAP":
+				bitmap = true
+			}
+		}
+	}
+	if rows != g.bounds.Dy() {
+		panic("invalid bitmap data, height mismatch")
+	}
+
+	// XXX: We don't try to convert encodings, since we'd need x/text/encoding
+	// for the conversion tables, though most fonts are at least going to use
+	// supersets of ASCII. Use ISO10646-1 X11 fonts for proper Unicode support.
+	if encoding >= 0 {
+		p.font.glyphs[rune(encoding)] = g
+	}
+	if encoding == p.defaultChar {
+		p.font.fallback = g
+	}
+}
+
+// https://en.wikipedia.org/wiki/Glyph_Bitmap_Distribution_Format
+// https://www.adobe.com/content/dam/acom/en/devnet/font/pdfs/5005.BDF_Spec.pdf
+func (p *bdfParser) parse() {
+	if !p.readLine() || len(p.tokens) != 2 || p.tokens[0] != "STARTFONT" {
+		panic("invalid header")
+	}
+	if p.tokens[1] != "2.1" && p.tokens[1] != "2.2" {
+		panic("unsupported version number")
+	}
+	for p.readLine() && p.tokens[0] != "ENDFONT" {
+		switch p.tokens[0] {
+		case "FONT":
+			if len(p.tokens) < 2 {
+				panic("insufficient arguments")
+			}
+			p.font.Name = p.tokens[1]
+		case "FONTBOUNDINGBOX":
+			// There's no guarantee that this includes all BBXs.
+			p.defaultBounds = p.readBBX()
+		case "METRICSSET":
+			if len(p.tokens) < 2 {
+				panic("insufficient arguments")
+			}
+			if p.tokens[1] == "1" {
+				panic("purely vertical fonts are unsupported")
+			}
+		case "DWIDTH":
+			p.defaultAdvance = p.readDwidth()
+		case "STARTPROPERTIES":
+			p.parseProperties()
+		case "STARTCHAR":
+			p.parseChar()
+		}
+	}
+	if p.font.Name == "" {
+		panic("the font file doesn't contain the font's name")
+	}
+	if len(p.font.glyphs) == 0 {
+		panic("the font file doesn't seem to contain any glyphs")
+	}
+}
+
+func NewFromBDF(r io.Reader) (f *Font, err error) {
+	p := bdfParser{
+		scanner:     bufio.NewScanner(r),
+		font:        &Font{glyphs: make(map[rune]glyph)},
+		defaultChar: -1,
+	}
+	defer func() {
+		if r := recover(); r != nil {
+			var ok bool
+			if err, ok = r.(error); !ok {
+				err = fmt.Errorf("%v", r)
+			}
+		}
+		if err != nil {
+			err = fmt.Errorf("line %d: %s", p.line, err)
+		}
+	}()
+
+	p.parse()
+	return p.font, nil
+}