Button can be drawn without horizontal padding around its text.

CHANGELOG.md

@@ -14,6 +14,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - the `button` widget allows users to specify multiple trigger keys.
 - the `button` widget can now be drawn without the shadow and the pressing the
   animation.
+- the `button` widget can now be drawn without horizontal padding around its
+  text.
 
 ## [0.13.0] - 17-Nov-2020
 

widgets/button/button.go

@@ -143,7 +143,8 @@ func (b *Button) Draw(cvs *canvas.Canvas, meta *widgetapi.Meta) error {
 		return err
 	}
 
-	textAr := image.Rect(buttonAr.Min.X+1, buttonAr.Min.Y, buttonAr.Dx()-1, buttonAr.Max.Y)
+	pad := b.opts.textHorizontalPadding
+	textAr := image.Rect(buttonAr.Min.X+pad, buttonAr.Min.Y, buttonAr.Dx()-pad, buttonAr.Max.Y)
 	start, err := alignfor.Text(textAr, b.text, align.HorizontalCenter, align.VerticalMiddle)
 	if err != nil {
 		return err
@@ -223,7 +224,7 @@ func (b *Button) shadowWidth() int {
 func (b *Button) Options() widgetapi.Options {
 	// No need to lock, as the height and width get fixed when New is called.
 
-	width := b.opts.width + b.shadowWidth()
+	width := b.opts.width + b.shadowWidth() + 2*b.opts.textHorizontalPadding
 	height := b.opts.height + b.shadowWidth()
 	return widgetapi.Options{
 		MinimumSize:  image.Point{width, height},

widgets/button/button_test.go

@@ -115,6 +115,15 @@ func TestButton(t *testing.T) {
 			canvas:     image.Rect(0, 0, 1, 1),
 			wantNewErr: true,
 		},
+		{
+			desc:     "New fails with negative textHorizontalPadding",
+			callback: &callbackTracker{},
+			opts: []Option{
+				TextHorizontalPadding(-1),
+			},
+			canvas:     image.Rect(0, 0, 1, 1),
+			wantNewErr: true,
+		},
 		{
 			desc:        "draw fails on canvas too small",
 			callback:    &callbackTracker{},
@@ -934,11 +943,25 @@ func TestOptions(t *testing.T) {
 			},
 		},
 		{
-			desc: "custom width specified",
+			desc: "custom width specified with default padding",
 			text: "hello",
 			opts: []Option{
 				Width(10),
 			},
+			want: widgetapi.Options{
+				MinimumSize:  image.Point{13, 4},
+				MaximumSize:  image.Point{13, 4},
+				WantKeyboard: widgetapi.KeyScopeNone,
+				WantMouse:    widgetapi.MouseScopeGlobal,
+			},
+		},
+		{
+			desc: "custom width specified with custom padding",
+			text: "hello",
+			opts: []Option{
+				Width(10),
+				TextHorizontalPadding(0),
+			},
 			want: widgetapi.Options{
 				MinimumSize:  image.Point{11, 4},
 				MaximumSize:  image.Point{11, 4},
@@ -946,7 +969,21 @@ func TestOptions(t *testing.T) {
 				WantMouse:    widgetapi.MouseScopeGlobal,
 			},
 		},
-
+		{
+			desc: "without shadow or padding",
+			text: "hello",
+			opts: []Option{
+				Width(10),
+				TextHorizontalPadding(0),
+				DisableShadow(),
+			},
+			want: widgetapi.Options{
+				MinimumSize:  image.Point{10, 3},
+				MaximumSize:  image.Point{10, 3},
+				WantKeyboard: widgetapi.KeyScopeNone,
+				WantMouse:    widgetapi.MouseScopeGlobal,
+			},
+		},
 		{
 			desc: "doesn't want keyboard by default",
 			text: "hello",

widgets/button/formdemo/formdemo.go

@@ -60,6 +60,7 @@ func main() {
 		button.GlobalKeys('s', 'S'),
 		button.DisableShadow(),
 		button.Height(1),
+		button.TextHorizontalPadding(0),
 	)
 	if err != nil {
 		panic(err)
@@ -75,6 +76,7 @@ func main() {
 		button.GlobalKeys('c', 'C'),
 		button.DisableShadow(),
 		button.Height(1),
+		button.TextHorizontalPadding(0),
 	)
 	if err != nil {
 		panic(err)

widgets/button/options.go

@@ -42,19 +42,23 @@ func (o option) set(opts *options) {
 
 // options holds the provided options.
 type options struct {
-	fillColor     cell.Color
-	textColor     cell.Color
-	shadowColor   cell.Color
-	disableShadow bool
-	height        int
-	width         int
-	keys          map[keyboard.Key]bool
-	keyScope      widgetapi.KeyScope
-	keyUpDelay    time.Duration
+	fillColor             cell.Color
+	textColor             cell.Color
+	textHorizontalPadding int
+	shadowColor           cell.Color
+	disableShadow         bool
+	height                int
+	width                 int
+	keys                  map[keyboard.Key]bool
+	keyScope              widgetapi.KeyScope
+	keyUpDelay            time.Duration
 }
 
 // validate validates the provided options.
 func (o *options) validate() error {
+	if min := 0; o.textHorizontalPadding < min {
+		return fmt.Errorf("invalid textHorizontalPadding %d, must be %d <= textHorizontalPadding", o.textHorizontalPadding, min)
+	}
 	if min := 1; o.height < min {
 		return fmt.Errorf("invalid height %d, must be %d <= height", o.height, min)
 	}
@@ -76,13 +80,14 @@ type keyScope struct {
 // newOptions returns options with the default values set.
 func newOptions(text string) *options {
 	return &options{
-		fillColor:   cell.ColorNumber(117),
-		textColor:   cell.ColorBlack,
-		shadowColor: cell.ColorNumber(240),
-		height:      DefaultHeight,
-		width:       widthFor(text),
-		keyUpDelay:  DefaultKeyUpDelay,
-		keys:        map[keyboard.Key]bool{},
+		fillColor:             cell.ColorNumber(117),
+		textColor:             cell.ColorBlack,
+		textHorizontalPadding: DefaultTextHorizontalPadding,
+		shadowColor:           cell.ColorNumber(240),
+		height:                DefaultHeight,
+		width:                 widthFor(text),
+		keyUpDelay:            DefaultKeyUpDelay,
+		keys:                  map[keyboard.Key]bool{},
 	}
 }
 
@@ -122,6 +127,8 @@ func Height(cells int) Option {
 // Width sets the width of the button in cells.
 // Must be a positive non-zero integer.
 // Defaults to the auto-width based on the length of the text label.
+// Not all the width may be available to the text if TextHorizontalPadding is
+// set to a non-zero integer.
 func Width(cells int) Option {
 	return option(func(opts *options) {
 		opts.width = cells
@@ -211,7 +218,18 @@ func DisableShadow() Option {
 	})
 }
 
+// DefaultTextHorizontalPadding is the default value for the HorizontalPadding option.
+const DefaultTextHorizontalPadding = 1
+
+// TextHorizontalPadding sets padding on the left and right side of the
+// button's text as the amount of cells.
+func TextHorizontalPadding(p int) Option {
+	return option(func(opts *options) {
+		opts.textHorizontalPadding = p
+	})
+}
+
 // widthFor returns the required width for the specified text.
 func widthFor(text string) int {
-	return runewidth.StringWidth(text) + 2 // One empty cell at each side.
+	return runewidth.StringWidth(text)
 }