font/opentype: implement font.Face interface
This CL adds the type Face that implements the font.Face interface.
This CL also adds tests using gofont/goregular as an input font, using
github.com/golang/freetype/truetype as reference values.
Updates golang/go#22451.
Change-Id: I2a6945309331b251ec2ddec95b6e809ad10aa116
Reviewed-on: https://go-review.googlesource.com/73870
Reviewed-by: Nigel Tao <nigeltao@golang.org>
diff --git a/font/opentype/face.go b/font/opentype/face.go
new file mode 100644
index 0000000..88c28da
--- /dev/null
+++ b/font/opentype/face.go
@@ -0,0 +1,103 @@
+// Copyright 2017 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.
+
+package opentype
+
+import (
+ "image"
+
+ "golang.org/x/image/font"
+ "golang.org/x/image/font/sfnt"
+ "golang.org/x/image/math/fixed"
+)
+
+// FaceOptions describes the possible options given to NewFace when
+// creating a new font.Face from a sfnt.Font.
+type FaceOptions struct {
+ Size float64 // Size is the font size in points
+ DPI float64 // DPI is the dots per inch resolution
+ Hinting font.Hinting // Hinting selects how to quantize a vector font's glyph nodes
+}
+
+func defaultFaceOptions() *FaceOptions {
+ return &FaceOptions{
+ Size: 12,
+ DPI: 72,
+ Hinting: font.HintingNone,
+ }
+}
+
+// Face implements the font.Face interface for sfnt.Font values.
+type Face struct {
+ f *sfnt.Font
+ hinting font.Hinting
+ scale fixed.Int26_6
+
+ buf sfnt.Buffer
+}
+
+// NewFace returns a new font.Face for the given sfnt.Font.
+// if opts is nil, sensible defaults will be used.
+func NewFace(f *sfnt.Font, opts *FaceOptions) (font.Face, error) {
+ if opts == nil {
+ opts = defaultFaceOptions()
+ }
+ face := &Face{
+ f: f,
+ hinting: opts.Hinting,
+ scale: fixed.Int26_6(0.5 + (opts.Size * opts.DPI * 64 / 72)),
+ }
+ return face, nil
+}
+
+// Close satisfies the font.Face interface.
+func (f *Face) Close() error {
+ return nil
+}
+
+// Metrics satisfies the font.Face interface.
+func (f *Face) Metrics() font.Metrics {
+ m, err := f.f.Metrics(&f.buf, f.scale, f.hinting)
+ if err != nil {
+ return font.Metrics{}
+ }
+ return m
+}
+
+// Kern satisfies the font.Face interface.
+func (f *Face) Kern(r0, r1 rune) fixed.Int26_6 {
+ x0 := f.index(r0)
+ x1 := f.index(r1)
+ k, err := f.f.Kern(&f.buf, x0, x1, fixed.Int26_6(f.f.UnitsPerEm()), f.hinting)
+ if err != nil {
+ return 0
+ }
+ return k
+}
+
+// Glyph satisfies the font.Face interface.
+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) {
+ panic("not implemented")
+}
+
+// GlyphBounds satisfies the font.Face interface.
+func (f *Face) GlyphBounds(r rune) (bounds fixed.Rectangle26_6, advance fixed.Int26_6, ok bool) {
+ advance, ok = f.GlyphAdvance(r)
+ if !ok {
+ return bounds, advance, ok
+ }
+ panic("not implemented")
+}
+
+// GlyphAdvance satisfies the font.Face interface.
+func (f *Face) GlyphAdvance(r rune) (advance fixed.Int26_6, ok bool) {
+ idx := f.index(r)
+ advance, err := f.f.GlyphAdvance(&f.buf, idx, f.scale, f.hinting)
+ return advance, err == nil
+}
+
+func (f *Face) index(r rune) sfnt.GlyphIndex {
+ x, _ := f.f.GlyphIndex(&f.buf, r)
+ return x
+}
diff --git a/font/opentype/face_test.go b/font/opentype/face_test.go
new file mode 100644
index 0000000..224b0f2
--- /dev/null
+++ b/font/opentype/face_test.go
@@ -0,0 +1,90 @@
+// Copyright 2017 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.
+
+package opentype
+
+import (
+ "testing"
+
+ "golang.org/x/image/font"
+ "golang.org/x/image/font/gofont/goregular"
+ "golang.org/x/image/font/sfnt"
+ "golang.org/x/image/math/fixed"
+)
+
+var (
+ regular font.Face
+)
+
+func init() {
+ font, err := sfnt.Parse(goregular.TTF)
+ if err != nil {
+ panic(err)
+ }
+
+ regular, err = NewFace(font, defaultFaceOptions())
+ if err != nil {
+ panic(err)
+ }
+}
+
+func TestFaceGlyphAdvance(t *testing.T) {
+ for _, test := range []struct {
+ r rune
+ want fixed.Int26_6
+ }{
+ {' ', 213},
+ {'A', 512},
+ {'Á', 512},
+ {'Æ', 768},
+ {'i', 189},
+ {'x', 384},
+ } {
+ got, ok := regular.GlyphAdvance(test.r)
+ if !ok {
+ t.Errorf("could not get glyph advance width for %q", test.r)
+ continue
+ }
+
+ if got != test.want {
+ t.Errorf("%q: glyph advance width=%d. want=%d", test.r, got, test.want)
+ continue
+ }
+ }
+}
+
+func TestFaceKern(t *testing.T) {
+ // FIXME(sbinet) there is no kerning with gofont/goregular
+ for _, test := range []struct {
+ r1, r2 rune
+ want fixed.Int26_6
+ }{
+ {'A', 'A', 0},
+ {'A', 'V', 0},
+ {'V', 'A', 0},
+ {'A', 'v', 0},
+ {'W', 'a', 0},
+ {'W', 'i', 0},
+ {'Y', 'i', 0},
+ {'f', '(', 0},
+ {'f', 'f', 0},
+ {'f', 'i', 0},
+ {'T', 'a', 0},
+ {'T', 'e', 0},
+ } {
+ got := regular.Kern(test.r1, test.r2)
+ if got != test.want {
+ t.Errorf("(%q, %q): glyph kerning=%d. want=%d", test.r1, test.r2, got, test.want)
+ continue
+ }
+ }
+}
+
+func TestFaceMetrics(t *testing.T) {
+ want := font.Metrics{Height: 768, Ascent: 726, Descent: 162}
+ got := regular.Metrics()
+ if got != want {
+ t.Fatalf("metrics failed. got=%#v. want=%#v", got, want)
+ }
+}
diff --git a/font/opentype/opentype.go b/font/opentype/opentype.go
new file mode 100644
index 0000000..452e952
--- /dev/null
+++ b/font/opentype/opentype.go
@@ -0,0 +1,7 @@
+// Copyright 2017 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.
+
+// Package opentype implements the font.Face interface based on SFNT
+// font file formats.
+package opentype // import "golang.org/x/image/font/opentype"
