text,widget/material: make font collections explicit

Before this change, package font implemented a global font registry,
with the usual problems of package global state.

This change deletes the global registry and introduces the text.Collection
type for representing a list of fonts and their faces. Collection exports
Lookup that finds the closest match and its face.

The existing FontRegistry is renamed to Cache to reflect its new limited
functionality: a cache of shapes and measurements on top of a Collection.

Then, material.NewTheme is changed to take a Collection and initialize
a Cache.

Updates gio#19 because multiple windows require a separate (writable) Cache per
window, while (read-only) Collections may be shared.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

font/font.go

@@ -1,36 +0,0 @@
-// SPDX-License-Identifier: Unlicense OR MIT
-
-// Package font implements a central font registry.
-package font
-
-import (
-	"sync"
-
-	"gioui.org/text"
-)
-
-var (
-	mu          sync.Mutex
-	initialized bool
-	shaper      = new(text.FontRegistry)
-)
-
-// Default returns a singleton *text.Shaper that contains
-// the registered fonts.
-func Default() *text.FontRegistry {
-	mu.Lock()
-	defer mu.Unlock()
-	initialized = true
-	return shaper
-}
-
-// Register a face. Register panics if Default has been
-// called.
-func Register(font text.Font, face text.Face) {
-	mu.Lock()
-	defer mu.Unlock()
-	if initialized {
-		panic("Register must be called before Default")
-	}
-	shaper.Register(font, face)
-}

font/gofont/gofont.go

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: Unlicense OR MIT
 
-// Package gofont registers the Go fonts in the font registry.
+// Package gofont exports the Go fonts as a text.Collection.
 //
 // See https://blog.golang.org/go-fonts for a description of the
 // fonts, and the golang.org/x/image/font/gofont packages for the
@@ -9,8 +9,8 @@ package gofont
 
 import (
 	"fmt"
+	"sync"
 
-	"gioui.org/font"
 	"gioui.org/font/opentype"
 	"gioui.org/text"
 	"golang.org/x/image/font/gofont/gobold"
@@ -27,27 +27,37 @@ import (
 	"golang.org/x/image/font/gofont/gosmallcapsitalic"
 )
 
-func Register() {
+var (
-	register(text.Font{}, goregular.TTF)
+	once       sync.Once
-	register(text.Font{Style: text.Italic}, goitalic.TTF)
+	collection *text.Collection
-	register(text.Font{Weight: text.Bold}, gobold.TTF)
+)
-	register(text.Font{Style: text.Italic, Weight: text.Bold}, gobolditalic.TTF)
+
-	register(text.Font{Weight: text.Medium}, gomedium.TTF)
+func Collection() *text.Collection {
-	register(text.Font{Weight: text.Medium, Style: text.Italic}, gomediumitalic.TTF)
+	once.Do(func() {
-	register(text.Font{Variant: "Mono"}, gomono.TTF)
+		c := new(text.Collection)
-	register(text.Font{Variant: "Mono", Weight: text.Bold}, gomonobold.TTF)
+		register(c, text.Font{}, goregular.TTF)
-	register(text.Font{Variant: "Mono", Weight: text.Bold, Style: text.Italic}, gomonobolditalic.TTF)
+		register(c, text.Font{Style: text.Italic}, goitalic.TTF)
-	register(text.Font{Variant: "Mono", Style: text.Italic}, gomonoitalic.TTF)
+		register(c, text.Font{Weight: text.Bold}, gobold.TTF)
-	register(text.Font{Variant: "Mono", Style: text.Italic}, gomonoitalic.TTF)
+		register(c, text.Font{Style: text.Italic, Weight: text.Bold}, gobolditalic.TTF)
-	register(text.Font{Variant: "Smallcaps"}, gosmallcaps.TTF)
+		register(c, text.Font{Weight: text.Medium}, gomedium.TTF)
-	register(text.Font{Variant: "Smallcaps", Style: text.Italic}, gosmallcapsitalic.TTF)
+		register(c, text.Font{Weight: text.Medium, Style: text.Italic}, gomediumitalic.TTF)
+		register(c, text.Font{Variant: "Mono"}, gomono.TTF)
+		register(c, text.Font{Variant: "Mono", Weight: text.Bold}, gomonobold.TTF)
+		register(c, text.Font{Variant: "Mono", Weight: text.Bold, Style: text.Italic}, gomonobolditalic.TTF)
+		register(c, text.Font{Variant: "Mono", Style: text.Italic}, gomonoitalic.TTF)
+		register(c, text.Font{Variant: "Mono", Style: text.Italic}, gomonoitalic.TTF)
+		register(c, text.Font{Variant: "Smallcaps"}, gosmallcaps.TTF)
+		register(c, text.Font{Variant: "Smallcaps", Style: text.Italic}, gosmallcapsitalic.TTF)
+		collection = c
+	})
+	return collection
 }
 
-func register(fnt text.Font, ttf []byte) {
+func register(c *text.Collection, fnt text.Font, ttf []byte) {
 	face, err := opentype.Parse(ttf)
 	if err != nil {
 		panic(fmt.Sprintf("failed to parse font: %v", err))
 	}
 	fnt.Typeface = "Go"
-	font.Register(fnt, face)
+	c.Register(fnt, face)
 }

text/shaper.go

@@ -28,94 +28,118 @@ type Shaper interface {
 	Metrics(font Font, size fixed.Int26_6) font.Metrics
 }
 
-// FontRegistry implements layout and shaping of text from a set of
+// Collection maps Fonts to Faces.
+type Collection struct {
+	def   Typeface
+	faces map[Font]Face
+}
+
+// Cache implements cached layout and shaping of text from a set of
 // registered fonts.
 //
-// If a font matches no registered shape, FontRegistry falls back to the
+// If a font matches no registered shape, Cache falls back to the
 // first registered face.
 //
 // The LayoutString and ShapeString results are cached and re-used if
 // possible.
-type FontRegistry struct {
+type Cache struct {
-	def   Typeface
+	col   *Collection
-	faces map[Font]*face
+	faces map[Font]*faceCache
 }
 
-type face struct {
+type faceCache struct {
-	face        Face
 	layoutCache layoutCache
 	pathCache   pathCache
 }
 
-func (s *FontRegistry) Register(font Font, tf Face) {
+func (c *Collection) Register(font Font, tf Face) {
-	if s.faces == nil {
+	if c.faces == nil {
-		s.def = font.Typeface
+		c.def = font.Typeface
-		s.faces = make(map[Font]*face)
+		c.faces = make(map[Font]Face)
 	}
 	if font.Weight == 0 {
 		font.Weight = Normal
 	}
-	s.faces[font] = &face{
+	c.faces[font] = tf
-		face: tf,
+}
+
+// Lookup a font and return the effective font and its
+// font face.
+func (c *Collection) Lookup(font Font) (Font, Face) {
+	var f Face
+	font, f = c.faceForStyle(font)
+	if f == nil {
+		font.Typeface = c.def
+		font, f = c.faceForStyle(font)
 	}
+	return font, f
 }
 
-func (s *FontRegistry) Layout(font Font, size fixed.Int26_6, maxWidth int, txt io.Reader) ([]Line, error) {
+func (c *Collection) faceForStyle(font Font) (Font, Face) {
-	tf := s.faceForFont(font)
+	tf := c.faces[font]
-	return tf.face.Layout(size, maxWidth, txt)
-}
-
-func (s *FontRegistry) Shape(font Font, size fixed.Int26_6, layout []Glyph) op.CallOp {
-	tf := s.faceForFont(font)
-	return tf.face.Shape(size, layout)
-}
-
-func (s *FontRegistry) LayoutString(font Font, size fixed.Int26_6, maxWidth int, str string) []Line {
-	tf := s.faceForFont(font)
-	return tf.layout(size, maxWidth, str)
-}
-
-func (s *FontRegistry) ShapeString(font Font, size fixed.Int26_6, str string, layout []Glyph) op.CallOp {
-	tf := s.faceForFont(font)
-	return tf.shape(size, str, layout)
-}
-
-func (s *FontRegistry) Metrics(font Font, size fixed.Int26_6) font.Metrics {
-	tf := s.faceForFont(font)
-	return tf.metrics(size)
-}
-
-func (s *FontRegistry) faceForStyle(font Font) *face {
-	tf := s.faces[font]
 	if tf == nil {
 		font := font
 		font.Weight = Normal
-		tf = s.faces[font]
+		tf = c.faces[font]
 	}
 	if tf == nil {
 		font := font
 		font.Style = Regular
-		tf = s.faces[font]
+		tf = c.faces[font]
 	}
 	if tf == nil {
 		font := font
 		font.Style = Regular
 		font.Weight = Normal
-		tf = s.faces[font]
+		tf = c.faces[font]
 	}
-	return tf
+	return font, tf
 }
 
-func (s *FontRegistry) faceForFont(font Font) *face {
+func NewCache(fonts *Collection) *Cache {
-	tf := s.faceForStyle(font)
+	return &Cache{
-	if tf == nil {
+		col:   fonts,
-		font.Typeface = s.def
+		faces: make(map[Font]*faceCache),
-		tf = s.faceForStyle(font)
 	}
-	return tf
 }
 
-func (t *face) layout(ppem fixed.Int26_6, maxWidth int, str string) []Line {
+func (s *Cache) Layout(font Font, size fixed.Int26_6, maxWidth int, txt io.Reader) ([]Line, error) {
+	_, face := s.faceForFont(font)
+	return face.Layout(size, maxWidth, txt)
+}
+
+func (s *Cache) Shape(font Font, size fixed.Int26_6, layout []Glyph) op.CallOp {
+	_, face := s.faceForFont(font)
+	return face.Shape(size, layout)
+}
+
+func (s *Cache) LayoutString(font Font, size fixed.Int26_6, maxWidth int, str string) []Line {
+	cache, face := s.faceForFont(font)
+	return cache.layout(face, size, maxWidth, str)
+}
+
+func (s *Cache) ShapeString(font Font, size fixed.Int26_6, str string, layout []Glyph) op.CallOp {
+	cache, face := s.faceForFont(font)
+	return cache.shape(face, size, str, layout)
+}
+
+func (s *Cache) Metrics(font Font, size fixed.Int26_6) font.Metrics {
+	cache, face := s.faceForFont(font)
+	return cache.metrics(face, size)
+}
+
+func (s *Cache) faceForFont(font Font) (*faceCache, Face) {
+	var f Face
+	font, f = s.col.Lookup(font)
+	cache, exists := s.faces[font]
+	if !exists {
+		cache = new(faceCache)
+		s.faces[font] = cache
+	}
+	return cache, f
+}
+
+func (t *faceCache) layout(face Face, ppem fixed.Int26_6, maxWidth int, str string) []Line {
 	if t == nil {
 		return nil
 	}
@@ -127,12 +151,12 @@ func (t *face) layout(ppem fixed.Int26_6, maxWidth int, str string) []Line {
 	if l, ok := t.layoutCache.Get(lk); ok {
 		return l
 	}
-	l, _ := t.face.Layout(ppem, maxWidth, strings.NewReader(str))
+	l, _ := face.Layout(ppem, maxWidth, strings.NewReader(str))
 	t.layoutCache.Put(lk, l)
 	return l
 }
 
-func (t *face) shape(ppem fixed.Int26_6, str string, layout []Glyph) op.CallOp {
+func (t *faceCache) shape(face Face, ppem fixed.Int26_6, str string, layout []Glyph) op.CallOp {
 	if t == nil {
 		return op.CallOp{}
 	}
@@ -143,11 +167,11 @@ func (t *face) shape(ppem fixed.Int26_6, str string, layout []Glyph) op.CallOp {
 	if clip, ok := t.pathCache.Get(pk); ok {
 		return clip
 	}
-	clip := t.face.Shape(ppem, layout)
+	clip := face.Shape(ppem, layout)
 	t.pathCache.Put(pk, clip)
 	return clip
 }
 
-func (t *face) metrics(ppem fixed.Int26_6) font.Metrics {
+func (t *faceCache) metrics(face Face, ppem fixed.Int26_6) font.Metrics {
-	return t.face.Metrics(ppem)
+	return face.Metrics(ppem)
 }

widget/material/theme.go

@@ -6,7 +6,6 @@ import (
 	"image/color"
 
 	"gioui.org/f32"
-	"gioui.org/font"
 	"gioui.org/layout"
 	"gioui.org/op/paint"
 	"gioui.org/text"
@@ -30,9 +29,9 @@ type Theme struct {
 	radioUncheckedIcon    *widget.Icon
 }
 
-func NewTheme() *Theme {
+func NewTheme(col *text.Collection) *Theme {
 	t := &Theme{
-		Shaper: font.Default(),
+		Shaper: text.NewCache(col),
 	}
 	t.Color.Primary = rgb(0x3f51b5)
 	t.Color.Text = rgb(0x000000)