ui/text: rename Center Alignment to Middle and drop IsNewline

Middle matches the similar layout.Middle constant, and IsNewline is
too simple to export.

Add documentation while we're here.

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

ui/measure/measure.go

@@ -179,7 +179,7 @@ func layoutText(ppem fixed.Int26_6, str string, f *opentype, opts text.LayoutOpt
 	}
 	for prev.idx < len(str) {
 		c, s := utf8.DecodeRuneInString(str[prev.idx:])
-		nl := text.IsNewline(c)
+		nl := c == '\n'
 		if opts.SingleLine && nl {
 			nl = false
 			c = ' '

ui/text/editor.go

@@ -334,7 +334,7 @@ func (e *Editor) layoutText() {
 		// up all available space.
 		if len(s) > 0 {
 			r, _ := utf8.DecodeLastRuneInString(s)
-			if !IsNewline(r) {
+			if r != '\n' {
 				dims.Size.X = e.maxWidth
 				break
 			}

ui/text/label.go

@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: Unlicense OR MIT
 
+// Package text implements text widgets.
 package text
 
 import (
@@ -15,12 +16,20 @@ import (
 	"golang.org/x/image/math/fixed"
 )
 
+// Label is a widget for laying out and drawing text.
 type Label struct {
-	Face      Face
-	Material  ui.MacroOp
+	// Face define the font and style of the text.
+	Face Face
+	// Material is a macro recording the material to draw the
+	// text. Use a ColorOp for colored text.
+	Material ui.MacroOp
+	// Alignment specify the text alignment.
 	Alignment Alignment
-	Text      string
-	MaxLines  int
+	// Text is the string to draw.
+	Text string
+	// MaxLines specify the maximum number of lines the text
+	// may fill.
+	MaxLines int
 
 	it lineIterator
 }

ui/text/measure.go

@@ -11,6 +11,7 @@ import (
 	"golang.org/x/image/math/fixed"
 )
 
+// A Line contains the measurements of a line of text.
 type Line struct {
 	Text String
 	// Width is the width of the line.
@@ -25,22 +26,31 @@ type Line struct {
 }
 
 type String struct {
-	String   string
+	String string
+	// Advances contain the advance of each rune in String.
 	Advances []fixed.Int26_6
 }
 
+// A Layout contains the measurements of a body of text as
+// a list of Lines.
 type Layout struct {
 	Lines []Line
 }
 
+// LayoutOptions specify the constraints of a text layout.
 type LayoutOptions struct {
-	MaxWidth   int
+	// MaxWidth set the maximum width of the layout.
+	MaxWidth int
+	// SingleLine specify that line breaks are ignored.
 	SingleLine bool
 }
 
 type Face interface {
-	Layout(str string, opts LayoutOptions) *Layout
-	Path(str String) ui.MacroOp
+	// Layout returns the text layout for a string given a set of
+	// options.
+	Layout(s string, opts LayoutOptions) *Layout
+	// Path returns the ClipOp outline of a text recorded in a macro.
+	Path(s String) ui.MacroOp
 }
 
 type Alignment uint8
@@ -48,7 +58,7 @@ type Alignment uint8
 const (
 	Start Alignment = iota
 	End
-	Center
+	Middle
 )
 
 func linesDimens(lines []Line) layout.Dimens {
@@ -77,14 +87,10 @@ func linesDimens(lines []Line) layout.Dimens {
 	}
 }
 
-func IsNewline(r rune) bool {
-	return r == '\n'
-}
-
 func align(align Alignment, width fixed.Int26_6, maxWidth int) fixed.Int26_6 {
 	mw := fixed.I(maxWidth)
 	switch align {
-	case Center:
+	case Middle:
 		return fixed.I(((mw - width) / 2).Floor())
 	case End:
 		return fixed.I((mw - width).Floor())
@@ -94,3 +100,16 @@ func align(align Alignment, width fixed.Int26_6, maxWidth int) fixed.Int26_6 {
 		panic(fmt.Errorf("unknown alignment %v", align))
 	}
 }
+
+func (a Alignment) String() string {
+	switch a {
+	case Start:
+		return "Start"
+	case End:
+		return "End"
+	case Middle:
+		return "Middle"
+	default:
+		panic("unreachable")
+	}
+}