added svg formatter

basic version without any options. colors and font-styles seem to be ok.
rough support for text background in styles like `murphy` using predrawn
rectangles (svg has no text background attribute).

things to improve:
- svg width attribute (`<svg width=""`)
- linenumbers
- highlighting
- embedded font
- tabwidth option
- margins?
- better position/width calculation (rectangles not correctly drawn on
resize)

cmd/chroma/main.go

@@ -64,6 +64,8 @@ command, for Go.
 		HTMLBaseLine              int    `help:"Base line number." default:"1"`
 		HTMLPreventSurroundingPre bool   `help:"Prevent the surrounding pre tag."`
 
+		SVG bool `help:"Output SVG representation of tokens."`
+
 		Files []string `arg:"" optional:"" help:"Files to highlight." type:"existingfile"`
 	}
 )
@@ -123,6 +125,10 @@ func main() {
 		cli.Formatter = "html"
 	}
 
+	if cli.SVG {
+		cli.Formatter = "svg"
+	}
+
 	// Retrieve user-specified style, clone it, and add some overrides.
 	builder := styles.Get(cli.Style).Builder()
 	if cli.HTMLHighlightStyle != "" {

formatters/api.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/alecthomas/chroma"
 	"github.com/alecthomas/chroma/formatters/html"
+	"github.com/alecthomas/chroma/formatters/svg"
 )
 
 var (
@@ -20,6 +21,7 @@ var (
 	}))
 	// Default HTML formatter outputs self-contained HTML.
 	htmlFull = Register("html", html.New(html.Standalone(), html.WithClasses())) // nolint
+	Svg      = Register("svg", svg.New())
 )
 
 // Fallback formatter.

formatters/svg/svg.go

@@ -0,0 +1,145 @@
+package svg
+
+import (
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/alecthomas/chroma"
+)
+
+// Option sets an option of the SVG formatter.
+type Option func(f *Formatter)
+
+// New SVG formatter.
+func New(options ...Option) *Formatter {
+	f := &Formatter{}
+	for _, option := range options {
+		option(f)
+	}
+	return f
+}
+
+// Formatter that generates SVG.
+type Formatter struct {
+}
+
+func (f *Formatter) Format(w io.Writer, style *chroma.Style, iterator chroma.Iterator) (err error) {
+	defer func() {
+		if perr := recover(); perr != nil {
+			err = perr.(error)
+		}
+	}()
+	f.writeSVG(w, style, iterator.Tokens())
+	return err
+}
+
+var svgEscaper = strings.NewReplacer(
+	`&`, "&",
+	`<`, "&lt;",
+	`>`, "&gt;",
+	`"`, "&quot;",
+	` `, "&#160;",
+	`	`, "&#160;&#160;&#160;&#160;",
+)
+
+// EscapeString escapes special characters.
+func escapeString(s string) string {
+	return svgEscaper.Replace(s)
+}
+
+func (f *Formatter) writeSVG(w io.Writer, style *chroma.Style, tokens []chroma.Token) { // nolint: gocyclo
+	svgStyles := f.styleToSVG(style)
+	lines := chroma.SplitTokensIntoLines(tokens)
+
+	fmt.Fprint(w, "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n")
+	fmt.Fprint(w, "<!DOCTYPE svg PUBLIC \"-//W3C//DTD SVG 1.0//EN\" \"http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/svg10.dtd\">\n")
+	fmt.Fprintf(w, "<svg height=\"%d\" xmlns=\"http://www.w3.org/2000/svg\">\n", len(lines)*22)
+	fmt.Fprintf(w, "<rect width=\"100%%\" height=\"100%%\" fill=\"%s\"/>\n", style.Get(chroma.Background).Background.String())
+	fmt.Fprintf(w, "<g font-family=\"Consolas, Monaco, Lucida Console, Liberation Mono, DejaVu Sans Mono, Bitstream Vera Sans Mono, Courier New, monospace\" font-size=\"14px\" fill=\"%s\">\n", style.Get(chroma.Text).Colour.String())
+
+	f.writeTokenBackgrounds(w, lines, style)
+
+	for index, tokens := range lines {
+		fmt.Fprintf(w, "<text x=\"0\" y=\"%d\" xml:space=\"preserve\">", (14+7)*(index+1))
+
+		for _, token := range tokens {
+			text := escapeString(token.String())
+			attr := f.styleAttr(svgStyles, token.Type)
+			if attr != "" {
+				text = fmt.Sprintf("<tspan %s>%s</tspan>", attr, text)
+			}
+			fmt.Fprint(w, text)
+		}
+		fmt.Fprint(w, "</text>")
+	}
+
+	fmt.Fprint(w, "\n</g>\n")
+	fmt.Fprint(w, "</svg>\n")
+}
+
+// There is no background attribute for text in SVG so simply calculate the position and text
+// of tokens with a background color that differs from the default and add a rectangle for each before
+// adding the token.
+func (f *Formatter) writeTokenBackgrounds(w io.Writer, lines [][]chroma.Token, style *chroma.Style) {
+	for index, tokens := range lines {
+		lineLength := 0
+		for _, token := range tokens {
+			length := len(strings.Replace(token.String(), `	`, "    ", -1))
+			tokenBackground := style.Get(token.Type).Background
+			if tokenBackground.IsSet() && tokenBackground != style.Get(chroma.Background).Background {
+				fmt.Fprintf(w, "<rect id=\"%s\" x=\"%d\" y=\"%d\" width=\"%d\" height=\"%d\" fill=\"%s\" />\n", escapeString(token.String()), lineLength*8, (14+7)*index+7, length*8, 14, style.Get(token.Type).Background.String())
+			}
+			lineLength += length
+		}
+	}
+}
+
+func (f *Formatter) styleAttr(styles map[chroma.TokenType]string, tt chroma.TokenType) string {
+	if _, ok := styles[tt]; !ok {
+		tt = tt.SubCategory()
+		if _, ok := styles[tt]; !ok {
+			tt = tt.Category()
+			if _, ok := styles[tt]; !ok {
+				return ""
+			}
+		}
+	}
+	return styles[tt]
+}
+
+func (f *Formatter) styleToSVG(style *chroma.Style) map[chroma.TokenType]string {
+	converted := map[chroma.TokenType]string{}
+	bg := style.Get(chroma.Background)
+	// Convert the style.
+	for t := range chroma.StandardTypes {
+		entry := style.Get(t)
+		if t != chroma.Background {
+			entry = entry.Sub(bg)
+		}
+		if entry.IsZero() {
+			continue
+		}
+		converted[t] = StyleEntryToSVG(entry)
+	}
+	return converted
+}
+
+// StyleEntryToSVG converts a chroma.StyleEntry to SVG attributes.
+func StyleEntryToSVG(e chroma.StyleEntry) string {
+	var styles []string
+
+	if e.Colour.IsSet() {
+		styles = append(styles, "fill=\""+e.Colour.String()+"\"")
+	}
+	if e.Bold == chroma.Yes {
+		styles = append(styles, "font-weight=\"bold\"")
+	}
+	if e.Italic == chroma.Yes {
+		styles = append(styles, "font-style=\"italic\"")
+	}
+	if e.Underline == chroma.Yes {
+		styles = append(styles, "text-decoration=\"underline\"")
+	}
+	return strings.Join(styles, " ")
+}