text: replace Family with Shaper, add Font, Face

There is now a single shaping implementation, Shaper, for all fonts, replacing
Family that only covered a single typeface.

A typeface is identified by a name, where the empty string denotes the
default typeface.

Font is introduced to specify a particular font from the typeface, style,
weight and size.

Face is changed to an interface for a particular layout and shaping method.
The text/shape package is renamed to text/opentype and contains a Face
implementation based on golang.org/x/image/font/sfnt.

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

text/lru.go

@@ -0,0 +1,121 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package text
+
+import (
+	"gioui.org/op/paint"
+	"golang.org/x/image/math/fixed"
+)
+
+type layoutCache struct {
+	m          map[layoutKey]*layoutElem
+	head, tail *layoutElem
+}
+
+type pathCache struct {
+	m          map[pathKey]*path
+	head, tail *path
+}
+
+type layoutElem struct {
+	next, prev *layoutElem
+	key        layoutKey
+	layout     *Layout
+}
+
+type path struct {
+	next, prev *path
+	key        pathKey
+	val        paint.ClipOp
+}
+
+type layoutKey struct {
+	ppem fixed.Int26_6
+	str  string
+	opts LayoutOptions
+}
+
+type pathKey struct {
+	ppem fixed.Int26_6
+	str  string
+}
+
+const maxSize = 1000
+
+func (l *layoutCache) Get(k layoutKey) (*Layout, bool) {
+	if lt, ok := l.m[k]; ok {
+		l.remove(lt)
+		l.insert(lt)
+		return lt.layout, true
+	}
+	return nil, false
+}
+
+func (l *layoutCache) Put(k layoutKey, lt *Layout) {
+	if l.m == nil {
+		l.m = make(map[layoutKey]*layoutElem)
+		l.head = new(layoutElem)
+		l.tail = new(layoutElem)
+		l.head.prev = l.tail
+		l.tail.next = l.head
+	}
+	val := &layoutElem{key: k, layout: lt}
+	l.m[k] = val
+	l.insert(val)
+	if len(l.m) > maxSize {
+		oldest := l.tail.next
+		l.remove(oldest)
+		delete(l.m, oldest.key)
+	}
+}
+
+func (l *layoutCache) remove(lt *layoutElem) {
+	lt.next.prev = lt.prev
+	lt.prev.next = lt.next
+}
+
+func (l *layoutCache) insert(lt *layoutElem) {
+	lt.next = l.head
+	lt.prev = l.head.prev
+	lt.prev.next = lt
+	lt.next.prev = lt
+}
+
+func (c *pathCache) Get(k pathKey) (paint.ClipOp, bool) {
+	if v, ok := c.m[k]; ok {
+		c.remove(v)
+		c.insert(v)
+		return v.val, true
+	}
+	return paint.ClipOp{}, false
+}
+
+func (c *pathCache) Put(k pathKey, v paint.ClipOp) {
+	if c.m == nil {
+		c.m = make(map[pathKey]*path)
+		c.head = new(path)
+		c.tail = new(path)
+		c.head.prev = c.tail
+		c.tail.next = c.head
+	}
+	val := &path{key: k, val: v}
+	c.m[k] = val
+	c.insert(val)
+	if len(c.m) > maxSize {
+		oldest := c.tail.next
+		c.remove(oldest)
+		delete(c.m, oldest.key)
+	}
+}
+
+func (c *pathCache) remove(v *path) {
+	v.next.prev = v.prev
+	v.prev.next = v.next
+}
+
+func (c *pathCache) insert(v *path) {
+	v.next = c.head
+	v.prev = c.head.prev
+	v.prev.next = v
+	v.next.prev = v
+}