Add parsing code for the Font Features, as well as new command

commands/features.go

@@ -0,0 +1,61 @@
+package commands
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/ConradIrwin/font/sfnt"
+)
+
+// Features prints the gpos/gsub tables (contains font features).
+func Features() {
+	if len(os.Args) < 2 {
+		panic(fmt.Errorf("Specify a font file"))
+	}
+
+	file, err := os.Open(os.Args[1])
+	if err != nil {
+		panic(fmt.Errorf("Failed to open font: %s", err))
+	}
+	defer file.Close()
+
+	font, err := sfnt.Parse(file)
+	if err != nil {
+		panic(fmt.Errorf("Failed to parse font: %s", err))
+	}
+
+	layoutTable(font, sfnt.TagGsub, "Glyph Substitution Table (GSUB)")
+	layoutTable(font, sfnt.TagGpos, "Glyph Positioning Table (GPOS)")
+}
+
+func layoutTable(font *sfnt.Font, tag sfnt.Tag, name string) {
+	if font.HasTable(tag) {
+		fmt.Printf("%s:\n", name)
+
+		t := font.Table(tag).(*sfnt.TableLayout)
+		for _, script := range t.Scripts {
+			fmt.Printf("\tScript %q%s:\n", script.Tag, bracketString(script))
+
+			fmt.Printf("\t\tDefault Language:\n")
+			for _, feature := range script.DefaultLanguage.Features {
+				fmt.Printf("\t\t\tFeature %q%s\n", feature.Tag, bracketString(feature))
+			}
+
+			for _, lang := range script.Languages {
+				fmt.Printf("\t\tLanguage %q%s:\n", lang.Tag, bracketString(lang))
+				for _, feature := range lang.Features {
+					fmt.Printf("\t\t\tFeature %q%s\n", feature.Tag, bracketString(feature))
+				}
+			}
+		}
+	} else {
+		fmt.Printf("No %s\n", name)
+	}
+}
+
+func bracketString(o fmt.Stringer) string {
+	if s := o.String(); s != "" {
+		return fmt.Sprintf(" (%s)", s)
+	}
+	return ""
+}

commands/info.go

@@ -11,7 +11,6 @@ import (
 )
 
 func Info() {
-
 	file, err := os.Open(os.Args[1])
 	if err != nil {
 		panic(err)

main.go

@@ -25,14 +25,17 @@ func main() {
 		commands.Stats()
 	case "metrics":
 		commands.Metrics()
+	case "features":
+		commands.Features()
 	default:
 		fmt.Println(`
-Usage: font [scrub|info|stats] font.[otf,ttf,woff]
+Usage: font [features|info|metrics|scrub|stats] font.[otf,ttf,woff]
 
+features: prints the gpos/gsub tables (contains font features)
 info: prints the name table (contains metadata)
 metrics: prints the hhea table (contains font metrics)
-stats: prints each table and the amount of space used
-scrub: remove the name table (saves significant space)`)
+scrub: remove the name table (saves significant space)
+stats: prints each table and the amount of space used`)
 	}
 
 }

sfnt/font.go

@@ -120,6 +120,18 @@ func (font *Font) OS2Table() *TableOS2 {
 	return font.tables[TagOS2].(*TableOS2)
 }
 
+// GposTable returns the Glyph Positioning table identified with the 'GPOS' tag.
+// This method will panic if the font doesn't have this table.
+func (font *Font) GposTable() *TableLayout {
+	return font.tables[TagGpos].(*TableLayout)
+}
+
+// GsubTable returns the Glyph Substitution table identified with the 'GSUB' tag.
+// This method will panic if the font doesn't have this table.
+func (font *Font) GsubTable() *TableLayout {
+	return font.tables[TagGsub].(*TableLayout)
+}
+
 func (font *Font) Table(tag Tag) Table {
 	return font.tables[tag]
 }