3 files changed, 111 insertions(+), 115 deletions(-)

M layout/example_test.go
M layout/flex.go
M widget/material/checkable.go

@@ 53,21 53,18 @@ func ExampleFlex() {
 	gtx := new(layout.Context)
 	gtx.Reset(nil, image.Point{X: 100, Y: 100})
 
-	flex := layout.Flex{}
-
-	// Rigid 10x10 widget.
-	child1 := flex.Rigid(gtx, func() {
-		fmt.Printf("Rigid: %v\n", gtx.Constraints.Width)
-		layoutWidget(gtx, 10, 10)
-	})
-
-	// Child with 50% space allowance.
-	child2 := flex.Flex(gtx, 0.5, func() {
-		fmt.Printf("50%%: %v\n", gtx.Constraints.Width)
-		layoutWidget(gtx, 10, 10)
-	})
-
-	flex.Layout(gtx, child1, child2)
+	layout.Flex{}.Layout(gtx,
+		// Rigid 10x10 widget.
+		layout.Rigid(func() {
+			fmt.Printf("Rigid: %v\n", gtx.Constraints.Width)
+			layoutWidget(gtx, 10, 10)
+		}),
+		// Child with 50% space allowance.
+		layout.Flexed(0.5, func() {
+			fmt.Printf("50%%: %v\n", gtx.Constraints.Width)
+			layoutWidget(gtx, 10, 10)
+		}),
+	)
 
 	// Output:
 	// Rigid: {0 100}

@@ 19,20 19,16 @@ type Flex struct {
 	Spacing Spacing
 	// Alignment is the alignment in the cross axis.
 	Alignment Alignment
-
-	size      int
-	rigidSize int
-	// fraction is the rounding error from a Flex weighting.
-	fraction float32
-
-	// Use an empty StackOp for tracking whether Rigid, Flex
-	// is called in the same layout scope as Layout.
-	begun bool
-	stack op.StackOp
 }
 
-// FlexChild is the layout result of a call End.
+// FlexChild is the descriptor for a Flex child.
 type FlexChild struct {
+	flex   bool
+	weight float32
+
+	widget Widget
+
+	// Scratch space.
 	macro op.MacroOp
 	dims  Dimensions
 }


@@ 60,74 56,82 @@ const (
 	SpaceEvenly
 )
 
-// Rigid lays out a widget with the main axis constrained to the range
-// from 0 to the remaining space.
-func (f *Flex) Rigid(gtx *Context, w Widget) FlexChild {
-	f.begin(gtx.Ops)
-	cs := gtx.Constraints
-	mainc := axisMainConstraint(f.Axis, cs)
-	mainMax := mainc.Max - f.size
-	if mainMax < 0 {
-		mainMax = 0
+// Rigid returns a Flex child with a maximal constraint of the
+// remaining space.
+func Rigid(widget Widget) FlexChild {
+	return FlexChild{
+		widget: widget,
 	}
-	cs = axisConstraints(f.Axis, Constraint{Max: mainMax}, axisCrossConstraint(f.Axis, cs))
-	var m op.MacroOp
-	m.Record(gtx.Ops)
-	dims := ctxLayout(gtx, cs, w)
-	m.Stop()
-	f.rigidSize += axisMain(f.Axis, dims.Size)
-	f.expand(dims)
-	return FlexChild{m, dims}
 }
 
-func (f *Flex) begin(ops *op.Ops) {
-	if f.begun {
-		return
+// Flexed returns a Flex child forced to take up a fraction of
+// the remaining space.
+func Flexed(weight float32, widget Widget) FlexChild {
+	return FlexChild{
+		flex:   true,
+		weight: weight,
+		widget: widget,
 	}
-	f.stack.Push(ops)
-	f.begun = true
 }
 
-// Flex is like Rigid, where the main axis size is also constrained to a
-// fraction of the space not taken up by Rigid children.
-func (f *Flex) Flex(gtx *Context, weight float32, w Widget) FlexChild {
-	f.begin(gtx.Ops)
-	cs := gtx.Constraints
-	mainc := axisMainConstraint(f.Axis, cs)
-	var flexSize int
-	if mainc.Max > f.size {
-		flexSize = mainc.Max - f.rigidSize
-		// Apply weight and add any leftover fraction from a
-		// previous Flex.
-		size := float32(flexSize)*weight + f.fraction
-		flexSize = int(size + .5)
-		f.fraction = size - float32(flexSize)
-		if max := mainc.Max - f.size; flexSize > max {
-			flexSize = max
+// Layout a list of children. The position of the children are
+// determined by the specified order, but Rigid children are laid out
+// before Flexed children.
+func (f Flex) Layout(gtx *Context, children ...FlexChild) {
+	size := 0
+	// Lay out Rigid children.
+	for i, child := range children {
+		if child.flex {
+			continue
 		}
+		cs := gtx.Constraints
+		mainc := axisMainConstraint(f.Axis, cs)
+		mainMax := mainc.Max - size
+		if mainMax < 0 {
+			mainMax = 0
+		}
+		cs = axisConstraints(f.Axis, Constraint{Max: mainMax}, axisCrossConstraint(f.Axis, cs))
+		var m op.MacroOp
+		m.Record(gtx.Ops)
+		dims := ctxLayout(gtx, cs, child.widget)
+		m.Stop()
+		sz := axisMain(f.Axis, dims.Size)
+		size += sz
+		children[i].macro = m
+		children[i].dims = dims
 	}
-	submainc := Constraint{Min: flexSize, Max: flexSize}
-	cs = axisConstraints(f.Axis, submainc, axisCrossConstraint(f.Axis, cs))
-	var m op.MacroOp
-	m.Record(gtx.Ops)
-	dims := ctxLayout(gtx, cs, w)
-	m.Stop()
-	f.expand(dims)
-	return FlexChild{m, dims}
-}
-
-// End a child by specifying its dimensions. Pass the returned layout result
-// to Layout.
-func (f *Flex) expand(dims Dimensions) {
-	sz := axisMain(f.Axis, dims.Size)
-	f.size += sz
-}
-
-// Layout a list of children. The order of the children determines their laid
-// out order.
-func (f *Flex) Layout(gtx *Context, children ...FlexChild) {
-	if len(children) > 0 {
-		f.stack.Pop()
+	rigidSize := size
+	// fraction is the rounding error from a Flex weighting.
+	var fraction float32
+	// Lay out Flexed children.
+	for i, child := range children {
+		if !child.flex {
+			continue
+		}
+		cs := gtx.Constraints
+		mainc := axisMainConstraint(f.Axis, cs)
+		var flexSize int
+		if mainc.Max > size {
+			flexSize = mainc.Max - rigidSize
+			// Apply weight and add any leftover fraction from a
+			// previous Flexed.
+			childSize := float32(flexSize)*child.weight + fraction
+			flexSize = int(childSize + .5)
+			fraction = childSize - float32(flexSize)
+			if max := mainc.Max - size; flexSize > max {
+				flexSize = max
+			}
+		}
+		submainc := Constraint{Min: flexSize, Max: flexSize}
+		cs = axisConstraints(f.Axis, submainc, axisCrossConstraint(f.Axis, cs))
+		var m op.MacroOp
+		m.Record(gtx.Ops)
+		dims := ctxLayout(gtx, cs, child.widget)
+		m.Stop()
+		sz := axisMain(f.Axis, dims.Size)
+		size += sz
+		children[i].macro = m
+		children[i].dims = dims
 	}
 	var maxCross int
 	var maxBaseline int


@@ 142,8 146,8 @@ func (f *Flex) Layout(gtx *Context, children ...FlexChild) {
 	cs := gtx.Constraints
 	mainc := axisMainConstraint(f.Axis, cs)
 	var space int
-	if mainc.Min > f.size {
-		space = mainc.Min - f.size
+	if mainc.Min > size {
+		space = mainc.Min - size
 	}
 	var mainSize int
 	switch f.Spacing {


@@ 199,9 203,6 @@ func (f *Flex) Layout(gtx *Context, children ...FlexChild) {
 	}
 	sz := axisPoint(f.Axis, mainSize, maxCross)
 	gtx.Dimensions = Dimensions{Size: sz, Baseline: sz.Y - maxBaseline}
-	f.begun = false
-	f.size = 0
-	f.rigidSize = 0
 }
 
 func axisPoint(a Axis, main, cross int) image.Point {

@@ 36,32 36,30 @@ func (c *checkable) layout(gtx *layout.Context, checked bool) {
 
 	hmin := gtx.Constraints.Width.Min
 	vmin := gtx.Constraints.Height.Min
-	flex := layout.Flex{Alignment: layout.Middle}
-
-	ico := flex.Rigid(gtx, func() {
-		layout.Align(layout.Center).Layout(gtx, func() {
-			layout.UniformInset(unit.Dp(2)).Layout(gtx, func() {
-				size := gtx.Px(c.Size)
-				icon.Color = c.IconColor
-				icon.Layout(gtx, unit.Px(float32(size)))
-				gtx.Dimensions = layout.Dimensions{
-					Size: image.Point{X: size, Y: size},
-				}
+	layout.Flex{Alignment: layout.Middle}.Layout(gtx,
+		layout.Rigid(func() {
+			layout.Align(layout.Center).Layout(gtx, func() {
+				layout.UniformInset(unit.Dp(2)).Layout(gtx, func() {
+					size := gtx.Px(c.Size)
+					icon.Color = c.IconColor
+					icon.Layout(gtx, unit.Px(float32(size)))
+					gtx.Dimensions = layout.Dimensions{
+						Size: image.Point{X: size, Y: size},
+					}
+				})
 			})
-		})
-	})
+		}),
 
-	lbl := flex.Rigid(gtx, func() {
-		gtx.Constraints.Width.Min = hmin
-		gtx.Constraints.Height.Min = vmin
-		layout.Align(layout.Start).Layout(gtx, func() {
-			layout.UniformInset(unit.Dp(2)).Layout(gtx, func() {
-				paint.ColorOp{Color: c.Color}.Add(gtx.Ops)
-				widget.Label{}.Layout(gtx, c.shaper, c.Font, c.Label)
+		layout.Rigid(func() {
+			gtx.Constraints.Width.Min = hmin
+			gtx.Constraints.Height.Min = vmin
+			layout.Align(layout.Start).Layout(gtx, func() {
+				layout.UniformInset(unit.Dp(2)).Layout(gtx, func() {
+					paint.ColorOp{Color: c.Color}.Add(gtx.Ops)
+					widget.Label{}.Layout(gtx, c.shaper, c.Font, c.Label)
+				})
 			})
-		})
-	})
-
-	flex.Layout(gtx, ico, lbl)
+		}),
+	)
 	pointer.Rect(image.Rectangle{Max: gtx.Dimensions.Size}).Add(gtx.Ops)
 }