material: make theme constructors stand-alone functions

The multitude of widget methods on Theme is unnecessary coupling in that all
possible widgets either have to be included in package material, or be
different than 3rd party widgets:

	var th *Theme

	// Core widget, calling a method on Theme.
	th.Button(...).Layout(...)

	// 3rd party widget, calling a function taking a Theme.
	datepicker.New(th, ...).Layout(...)

Another reason for the Theme methods was to enable a poor man's
theme replacement, so that you could use the same code for
compatible themes. For example,

	mat.Button(...).Layout(...)

would not need to change if the type of mat changed, as long as
the new type had a compatible method Button.

However, that point misses the fact that the mat variable had to
be declared somewhere, naming the theme package:

	var mat *material.Theme (or, say, *cocoa.Theme)

A better and complete way to replace a theme is to use import renaming.
For example, to replace the material theme with a hypothetical Windows
theme, replace

	import theme "gioui.org/widget/material"

with

	import theme "github.com/somebody/windows

This change moves all Theme widget methods to be standalone functions,
and renames the widget style types accordingly.

For example, instead of the method

	func (t *Theme) Button(...) Button

there is now a function

	func Button(t *Theme, ...) ButtonStyle

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

widget/material/button.go

@@ -17,7 +17,7 @@ import (
 	"gioui.org/widget"
 )
 
-type Button struct {
+type ButtonStyle struct {
 	Text string
 	// Color is the text color.
 	Color        color.RGBA
@@ -29,14 +29,14 @@ type Button struct {
 	shaper       text.Shaper
 }
 
-type ButtonLayout struct {
+type ButtonLayoutStyle struct {
 	Background   color.RGBA
 	Color        color.RGBA
 	CornerRadius unit.Value
 	Inset        layout.Inset
 }
 
-type IconButton struct {
+type IconButtonStyle struct {
 	Background color.RGBA
 	Color      color.RGBA
 	Icon       *widget.Icon
@@ -45,42 +45,42 @@ type IconButton struct {
 	Inset      layout.Inset
 }
 
-func (t *Theme) Button(txt string) Button {
+func Button(th *Theme, txt string) ButtonStyle {
-	return Button{
+	return ButtonStyle{
 		Text:         txt,
 		Color:        rgb(0xffffff),
 		CornerRadius: unit.Dp(4),
-		Background:   t.Color.Primary,
+		Background:   th.Color.Primary,
-		TextSize:     t.TextSize.Scale(14.0 / 16.0),
+		TextSize:     th.TextSize.Scale(14.0 / 16.0),
 		Inset: layout.Inset{
 			Top: unit.Dp(10), Bottom: unit.Dp(10),
 			Left: unit.Dp(12), Right: unit.Dp(12),
 		},
-		shaper: t.Shaper,
+		shaper: th.Shaper,
 	}
 }
 
-func (t *Theme) ButtonLayout() ButtonLayout {
+func ButtonLayout(th *Theme) ButtonLayoutStyle {
-	return ButtonLayout{
+	return ButtonLayoutStyle{
-		Background:   t.Color.Primary,
+		Background:   th.Color.Primary,
-		Color:        t.Color.InvText,
+		Color:        th.Color.InvText,
 		CornerRadius: unit.Dp(4),
 		Inset:        layout.UniformInset(unit.Dp(12)),
 	}
 }
 
-func (t *Theme) IconButton(icon *widget.Icon) IconButton {
+func IconButton(th *Theme, icon *widget.Icon) IconButtonStyle {
-	return IconButton{
+	return IconButtonStyle{
-		Background: t.Color.Primary,
+		Background: th.Color.Primary,
-		Color:      t.Color.InvText,
+		Color:      th.Color.InvText,
 		Icon:       icon,
 		Size:       unit.Dp(56),
 		Padding:    unit.Dp(16),
 	}
 }
 
-func (b Button) Layout(gtx *layout.Context, button *widget.Button) {
+func (b ButtonStyle) Layout(gtx *layout.Context, button *widget.Button) {
-	ButtonLayout{
+	ButtonLayoutStyle{
 		Background:   b.Background,
 		CornerRadius: b.CornerRadius,
 		Color:        b.Color,
@@ -90,7 +90,7 @@ func (b Button) Layout(gtx *layout.Context, button *widget.Button) {
 	})
 }
 
-func (b ButtonLayout) Layout(gtx *layout.Context, button *widget.Button, w layout.Widget) {
+func (b ButtonLayoutStyle) Layout(gtx *layout.Context, button *widget.Button, w layout.Widget) {
 	hmin := gtx.Constraints.Width.Min
 	vmin := gtx.Constraints.Height.Min
 	layout.Stack{Alignment: layout.Center}.Layout(gtx,
@@ -123,7 +123,7 @@ func (b ButtonLayout) Layout(gtx *layout.Context, button *widget.Button, w layou
 	)
 }
 
-func (b IconButton) Layout(gtx *layout.Context, button *widget.Button) {
+func (b IconButtonStyle) Layout(gtx *layout.Context, button *widget.Button) {
 	layout.Stack{Alignment: layout.Center}.Layout(gtx,
 		layout.Expanded(func() {
 			size := gtx.Constraints.Width.Min

widget/material/checkbox.go

@@ -8,26 +8,26 @@ import (
 	"gioui.org/widget"
 )
 
-type CheckBox struct {
+type CheckBoxStyle struct {
 	checkable
 }
 
-func (t *Theme) CheckBox(label string) CheckBox {
+func CheckBox(th *Theme, label string) CheckBoxStyle {
-	return CheckBox{
+	return CheckBoxStyle{
 		checkable{
 			Label:              label,
-			Color:              t.Color.Text,
+			Color:              th.Color.Text,
-			IconColor:          t.Color.Primary,
+			IconColor:          th.Color.Primary,
-			TextSize:           t.TextSize.Scale(14.0 / 16.0),
+			TextSize:           th.TextSize.Scale(14.0 / 16.0),
 			Size:               unit.Dp(26),
-			shaper:             t.Shaper,
+			shaper:             th.Shaper,
-			checkedStateIcon:   t.checkBoxCheckedIcon,
+			checkedStateIcon:   th.checkBoxCheckedIcon,
-			uncheckedStateIcon: t.checkBoxUncheckedIcon,
+			uncheckedStateIcon: th.checkBoxUncheckedIcon,
 		},
 	}
 }
 
-func (c CheckBox) Layout(gtx *layout.Context, checkBox *widget.CheckBox) {
+func (c CheckBoxStyle) Layout(gtx *layout.Context, checkBox *widget.CheckBox) {
 	c.layout(gtx, checkBox.Checked(gtx))
 	checkBox.Layout(gtx)
 }

widget/material/doc.go

@@ -22,12 +22,12 @@
 //
 //     theme := material.NewTheme(...)
 //
-//     th.Button("Click me!").Layout(gtx, button)
+//     material.Button(theme, "Click me!").Layout(gtx, button)
 //
 // Customization
 //
-// Quite often, a program needs to customize the theme provided defaults. Several
+// Quite often, a program needs to customize the theme-provided defaults. Several
-// options are available, depending on the nature of the change:
+// options are available, depending on the nature of the change.
 //
 // Mandatory parameters: Some parameters are not part of the widget state but
 // have no obvious default. In the program above, the button text is a
@@ -41,7 +41,7 @@
 // Widget-local parameters: For changing the look of a particular widget,
 // adjust the widget specific theme object:
 //
-//     btn := th.Button("Click me!")
+//     btn := material.Button(theme, "Click me!")
 //     btn.Font.Style = text.Italic
 //     btn.Layout(gtx)
 //
@@ -51,7 +51,7 @@
 //
 //     icon := material.NewIcon(...)
 //
-//     th.IconButton(icon).Layout(gtx, button)
+//     material.IconButton(theme, icon).Layout(gtx, button)
 //
 // Specialized widgets: Theme both define a generic Label method
 // that takes a text size, and specialized methods for standard text

widget/material/editor.go

@@ -13,7 +13,7 @@ import (
 	"gioui.org/widget"
 )
 
-type Editor struct {
+type EditorStyle struct {
 	Font     text.Font
 	TextSize unit.Value
 	// Color is the text color.
@@ -26,17 +26,17 @@ type Editor struct {
 	shaper text.Shaper
 }
 
-func (t *Theme) Editor(hint string) Editor {
+func Editor(th *Theme, hint string) EditorStyle {
-	return Editor{
+	return EditorStyle{
-		TextSize:  t.TextSize,
+		TextSize:  th.TextSize,
-		Color:     t.Color.Text,
+		Color:     th.Color.Text,
-		shaper:    t.Shaper,
+		shaper:    th.Shaper,
 		Hint:      hint,
-		HintColor: t.Color.Hint,
+		HintColor: th.Color.Hint,
 	}
 }
 
-func (e Editor) Layout(gtx *layout.Context, editor *widget.Editor) {
+func (e EditorStyle) Layout(gtx *layout.Context, editor *widget.Editor) {
 	var stack op.StackOp
 	stack.Push(gtx.Ops)
 	var macro op.MacroOp

widget/material/label.go

@@ -12,7 +12,7 @@ import (
 	"gioui.org/widget"
 )
 
-type Label struct {
+type LabelStyle struct {
 	// Face defines the text style.
 	Font text.Font
 	// Color is the text color.
@@ -27,52 +27,52 @@ type Label struct {
 	shaper text.Shaper
 }
 
-func (t *Theme) H1(txt string) Label {
+func H1(th *Theme, txt string) LabelStyle {
-	return t.Label(t.TextSize.Scale(96.0/16.0), txt)
+	return Label(th, th.TextSize.Scale(96.0/16.0), txt)
 }
 
-func (t *Theme) H2(txt string) Label {
+func H2(th *Theme, txt string) LabelStyle {
-	return t.Label(t.TextSize.Scale(60.0/16.0), txt)
+	return Label(th, th.TextSize.Scale(60.0/16.0), txt)
 }
 
-func (t *Theme) H3(txt string) Label {
+func H3(th *Theme, txt string) LabelStyle {
-	return t.Label(t.TextSize.Scale(48.0/16.0), txt)
+	return Label(th, th.TextSize.Scale(48.0/16.0), txt)
 }
 
-func (t *Theme) H4(txt string) Label {
+func H4(th *Theme, txt string) LabelStyle {
-	return t.Label(t.TextSize.Scale(34.0/16.0), txt)
+	return Label(th, th.TextSize.Scale(34.0/16.0), txt)
 }
 
-func (t *Theme) H5(txt string) Label {
+func H5(th *Theme, txt string) LabelStyle {
-	return t.Label(t.TextSize.Scale(24.0/16.0), txt)
+	return Label(th, th.TextSize.Scale(24.0/16.0), txt)
 }
 
-func (t *Theme) H6(txt string) Label {
+func H6(th *Theme, txt string) LabelStyle {
-	return t.Label(t.TextSize.Scale(20.0/16.0), txt)
+	return Label(th, th.TextSize.Scale(20.0/16.0), txt)
 }
 
-func (t *Theme) Body1(txt string) Label {
+func Body1(th *Theme, txt string) LabelStyle {
-	return t.Label(t.TextSize, txt)
+	return Label(th, th.TextSize, txt)
 }
 
-func (t *Theme) Body2(txt string) Label {
+func Body2(th *Theme, txt string) LabelStyle {
-	return t.Label(t.TextSize.Scale(14.0/16.0), txt)
+	return Label(th, th.TextSize.Scale(14.0/16.0), txt)
 }
 
-func (t *Theme) Caption(txt string) Label {
+func Caption(th *Theme, txt string) LabelStyle {
-	return t.Label(t.TextSize.Scale(12.0/16.0), txt)
+	return Label(th, th.TextSize.Scale(12.0/16.0), txt)
 }
 
-func (t *Theme) Label(size unit.Value, txt string) Label {
+func Label(th *Theme, size unit.Value, txt string) LabelStyle {
-	return Label{
+	return LabelStyle{
 		Text:     txt,
-		Color:    t.Color.Text,
+		Color:    th.Color.Text,
 		TextSize: size,
-		shaper:   t.Shaper,
+		shaper:   th.Shaper,
 	}
 }
 
-func (l Label) Layout(gtx *layout.Context) {
+func (l LabelStyle) Layout(gtx *layout.Context) {
 	paint.ColorOp{Color: l.Color}.Add(gtx.Ops)
 	tl := widget.Label{Alignment: l.Alignment, MaxLines: l.MaxLines}
 	tl.Layout(gtx, l.shaper, l.Font, l.TextSize, l.Text)

widget/material/progressbar.go

@@ -13,17 +13,17 @@ import (
 	"gioui.org/unit"
 )
 
-type ProgressBar struct {
+type ProgressBarStyle struct {
 	Color color.RGBA
 }
 
-func (t *Theme) ProgressBar() ProgressBar {
+func ProgressBar(th *Theme) ProgressBarStyle {
-	return ProgressBar{
+	return ProgressBarStyle{
-		Color: t.Color.Primary,
+		Color: th.Color.Primary,
 	}
 }
 
-func (b ProgressBar) Layout(gtx *layout.Context, progress int) {
+func (b ProgressBarStyle) Layout(gtx *layout.Context, progress int) {
 	shader := func(width float32, color color.RGBA) {
 		maxHeight := unit.Dp(4)
 		rr := float32(gtx.Px(unit.Dp(2)))

widget/material/radiobutton.go

@@ -8,31 +8,31 @@ import (
 	"gioui.org/widget"
 )
 
-type RadioButton struct {
+type RadioButtonStyle struct {
 	checkable
 	Key string
 }
 
 // RadioButton returns a RadioButton with a label. The key specifies
 // the value for the Enum.
-func (t *Theme) RadioButton(key, label string) RadioButton {
+func RadioButton(th *Theme, key, label string) RadioButtonStyle {
-	return RadioButton{
+	return RadioButtonStyle{
 		checkable: checkable{
 			Label: label,
 
-			Color:              t.Color.Text,
+			Color:              th.Color.Text,
-			IconColor:          t.Color.Primary,
+			IconColor:          th.Color.Primary,
-			TextSize:           t.TextSize.Scale(14.0 / 16.0),
+			TextSize:           th.TextSize.Scale(14.0 / 16.0),
 			Size:               unit.Dp(26),
-			shaper:             t.Shaper,
+			shaper:             th.Shaper,
-			checkedStateIcon:   t.radioCheckedIcon,
+			checkedStateIcon:   th.radioCheckedIcon,
-			uncheckedStateIcon: t.radioUncheckedIcon,
+			uncheckedStateIcon: th.radioUncheckedIcon,
 		},
 		Key: key,
 	}
 }
 
-func (r RadioButton) Layout(gtx *layout.Context, enum *widget.Enum) {
+func (r RadioButtonStyle) Layout(gtx *layout.Context, enum *widget.Enum) {
 	r.layout(gtx, enum.Value(gtx) == r.Key)
 	enum.Layout(gtx, r.Key)
 }