widget: [API] separate Float state update; remove min, max, invert parameters

This change allows users of Float to determine its state before Layout
by calling Update.

While here, remove the value transformation represented by the min, max,
invert parameters; they're too many arguments for a computation that
may as well be done by the user.

Remove Float.Pos; it is better to compute its value from the dimensions
returned by Float.Layout.

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

widget/float.go

@@ -9,59 +9,29 @@ import (
 	"gioui.org/io/pointer"
 	"gioui.org/layout"
 	"gioui.org/op/clip"
+	"gioui.org/unit"
 )
 
 // Float is for selecting a value in a range.
 type Float struct {
+	// Value is the value of the Float, in the [0; 1] range.
 	Value float32
 
-	drag    gesture.Drag
-	pos     float32 // position normalized to [0, 1]
-	length  float32
-	changed bool
+	drag   gesture.Drag
+	axis   layout.Axis
+	length float32
 }
 
 // Dragging returns whether the value is being interacted with.
 func (f *Float) Dragging() bool { return f.drag.Dragging() }
 
-// Layout updates the value according to drag events along the f's main axis.
-//
-// The range of f is set by the minimum constraints main axis value.
-func (f *Float) Layout(gtx layout.Context, axis layout.Axis, min, max float32, invert bool, pointerMargin int) layout.Dimensions {
+func (f *Float) Layout(gtx layout.Context, axis layout.Axis, pointerMargin unit.Dp) layout.Dimensions {
+	f.Update(gtx)
 	size := gtx.Constraints.Min
 	f.length = float32(axis.Convert(size).X)
+	f.axis = axis
 
-	var de *pointer.Event
-	for _, e := range f.drag.Events(gtx.Metric, gtx, gesture.Axis(axis)) {
-		if e.Kind == pointer.Press || e.Kind == pointer.Drag {
-			de = &e
-		}
-	}
-
-	value := f.Value
-	if de != nil {
-		xy := de.Position.X
-		if axis == layout.Vertical {
-			xy = f.length - de.Position.Y
-		}
-		if invert {
-			xy = f.length - xy
-		}
-		f.pos = xy / f.length
-		value = min + (max-min)*f.pos
-	} else if min != max {
-		f.pos = (value - min) / (max - min)
-	}
-	// Unconditionally call setValue in case min, max, or value changed.
-	f.setValue(value, min, max)
-
-	if f.pos < 0 {
-		f.pos = 0
-	} else if f.pos > 1 {
-		f.pos = 1
-	}
-
-	margin := axis.Convert(image.Pt(pointerMargin, 0))
+	margin := axis.Convert(image.Pt(gtx.Dp(pointerMargin), 0))
 	rect := image.Rectangle{
 		Min: margin.Mul(-1),
 		Max: size.Add(margin),
@@ -72,30 +42,26 @@ func (f *Float) Layout(gtx layout.Context, axis layout.Axis, min, max float32, i
 	return layout.Dimensions{Size: size}
 }
 
-func (f *Float) setValue(value, min, max float32) {
-	if min > max {
-		min, max = max, min
+// Update the Value according to drag events along the f's main axis.
+// The return value reports whether the value was changed.
+//
+// The range of f is set by the minimum constraints main axis value.
+func (f *Float) Update(gtx layout.Context) bool {
+	changed := false
+	for _, e := range f.drag.Events(gtx.Metric, gtx, gesture.Axis(f.axis)) {
+		if f.length > 0 && (e.Kind == pointer.Press || e.Kind == pointer.Drag) {
+			pos := e.Position.X
+			if f.axis == layout.Vertical {
+				pos = f.length - e.Position.Y
+			}
+			f.Value = pos / f.length
+			if f.Value < 0 {
+				f.Value = 0
+			} else if f.Value > 1 {
+				f.Value = 1
+			}
+			changed = true
+		}
 	}
-	if value < min {
-		value = min
-	} else if value > max {
-		value = max
-	}
-	if f.Value != value {
-		f.Value = value
-		f.changed = true
-	}
-}
-
-// Pos reports the selected position.
-func (f *Float) Pos() float32 {
-	return f.pos * f.length
-}
-
-// Changed reports whether the value has changed since
-// the last call to Changed.
-func (f *Float) Changed() bool {
-	changed := f.changed
-	f.changed = false
 	return changed
 }

widget/material/slider.go

@@ -16,10 +16,8 @@ import (
 )
 
 // Slider is for selecting a value in a range.
-func Slider(th *Theme, float *widget.Float, min, max float32) SliderStyle {
+func Slider(th *Theme, float *widget.Float) SliderStyle {
 	return SliderStyle{
-		Min:        min,
-		Max:        max,
 		Color:      th.Palette.ContrastBg,
 		Float:      float,
 		FingerSize: th.FingerSize,
@@ -27,35 +25,34 @@ func Slider(th *Theme, float *widget.Float, min, max float32) SliderStyle {
 }
 
 type SliderStyle struct {
-	Axis     layout.Axis
-	Min, Max float32
-	Invert   bool
-	Color    color.NRGBA
-	Float    *widget.Float
+	Axis  layout.Axis
+	Color color.NRGBA
+	Float *widget.Float
 
 	FingerSize unit.Dp
 }
 
 func (s SliderStyle) Layout(gtx layout.Context) layout.Dimensions {
-	thumbRadius := gtx.Dp(6)
+	const thumbRadius unit.Dp = 6
+	tr := gtx.Dp(thumbRadius)
 	trackWidth := gtx.Dp(2)
 
 	axis := s.Axis
 	// Keep a minimum length so that the track is always visible.
-	minLength := thumbRadius + 3*thumbRadius + thumbRadius
+	minLength := tr + 3*tr + tr
 	// Try to expand to finger size, but only if the constraints
 	// allow for it.
 	touchSizePx := min(gtx.Dp(s.FingerSize), axis.Convert(gtx.Constraints.Max).Y)
 	sizeMain := max(axis.Convert(gtx.Constraints.Min).X, minLength)
-	sizeCross := max(2*thumbRadius, touchSizePx)
+	sizeCross := max(2*tr, touchSizePx)
 	size := axis.Convert(image.Pt(sizeMain, sizeCross))
 
-	o := axis.Convert(image.Pt(thumbRadius, 0))
+	o := axis.Convert(image.Pt(tr, 0))
 	trans := op.Offset(o).Push(gtx.Ops)
-	gtx.Constraints.Min = axis.Convert(image.Pt(sizeMain-2*thumbRadius, sizeCross))
-	s.Float.Layout(gtx, axis, s.Min, s.Max, s.Invert, thumbRadius)
+	gtx.Constraints.Min = axis.Convert(image.Pt(sizeMain-2*tr, sizeCross))
+	dims := s.Float.Layout(gtx, axis, thumbRadius)
 	gtx.Constraints.Min = gtx.Constraints.Min.Add(axis.Convert(image.Pt(0, sizeCross)))
-	thumbPos := thumbRadius + int(s.Float.Pos())
+	thumbPos := tr + int(s.Float.Value*float32(axis.Convert(dims.Size).X))
 	trans.Pop()
 
 	color := s.Color
@@ -65,7 +62,7 @@ func (s SliderStyle) Layout(gtx layout.Context) layout.Dimensions {
 
 	rect := func(minx, miny, maxx, maxy int) image.Rectangle {
 		r := image.Rect(minx, miny, maxx, maxy)
-		if s.Invert != (axis == layout.Vertical) {
+		if axis == layout.Vertical {
 			r.Max.X, r.Min.X = sizeMain-r.Min.X, sizeMain-r.Max.X
 		}
 		r.Min = axis.Convert(r.Min)
@@ -75,7 +72,7 @@ func (s SliderStyle) Layout(gtx layout.Context) layout.Dimensions {
 
 	// Draw track before thumb.
 	track := rect(
-		thumbRadius, sizeCross/2-trackWidth/2,
+		tr, sizeCross/2-trackWidth/2,
 		thumbPos, sizeCross/2+trackWidth/2,
 	)
 	paint.FillShape(gtx.Ops, color, clip.Rect(track).Op())
@@ -83,15 +80,15 @@ func (s SliderStyle) Layout(gtx layout.Context) layout.Dimensions {
 	// Draw track after thumb.
 	track = rect(
 		thumbPos, axis.Convert(track.Min).Y,
-		sizeMain-thumbRadius, axis.Convert(track.Max).Y,
+		sizeMain-tr, axis.Convert(track.Max).Y,
 	)
 	paint.FillShape(gtx.Ops, f32color.MulAlpha(color, 96), clip.Rect(track).Op())
 
 	// Draw thumb.
 	pt := image.Pt(thumbPos, sizeCross/2)
 	thumb := rect(
-		pt.X-thumbRadius, pt.Y-thumbRadius,
-		pt.X+thumbRadius, pt.Y+thumbRadius,
+		pt.X-tr, pt.Y-tr,
+		pt.X+tr, pt.Y+tr,
 	)
 	paint.FillShape(gtx.Ops, color, clip.Ellipse(thumb).Op(gtx.Ops))