widget,widget/material: add Float and Slider

Signed-off-by: Gordon Klaus <gordon.klaus@gmail.com>

widget/material/slider.go

@@ -0,0 +1,109 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package material
+
+import (
+	"image"
+	"image/color"
+
+	"gioui.org/f32"
+	"gioui.org/layout"
+	"gioui.org/op"
+	"gioui.org/op/clip"
+	"gioui.org/op/paint"
+	"gioui.org/unit"
+	"gioui.org/widget"
+)
+
+// Slider is for selecting a value in a range.
+func Slider(th *Theme, float *widget.Float, min, max float32) SliderStyle {
+	return SliderStyle{
+		Min:   min,
+		Max:   max,
+		Color: th.Color.Primary,
+		Float: float,
+	}
+}
+
+type SliderStyle struct {
+	Min, Max float32
+	Color    color.RGBA
+	Float    *widget.Float
+}
+
+func (s SliderStyle) Layout(gtx layout.Context) layout.Dimensions {
+	thumbRadiusInt := gtx.Px(unit.Dp(6))
+	trackWidth := float32(gtx.Px(unit.Dp(2)))
+	thumbRadius := float32(thumbRadiusInt)
+	halfWidthInt := 2 * thumbRadiusInt
+	halfWidth := float32(halfWidthInt)
+
+	size := gtx.Constraints.Min
+	// Keep a minimum length so that the track is always visible.
+	minLength := halfWidthInt + 3*thumbRadiusInt + halfWidthInt
+	if size.X < minLength {
+		size.X = minLength
+	}
+	size.Y = 2 * halfWidthInt
+
+	st := op.Push(gtx.Ops)
+	op.Offset(f32.Pt(halfWidth, 0)).Add(gtx.Ops)
+	gtx.Constraints.Min = image.Pt(size.X-2*halfWidthInt, size.Y)
+	s.Float.Layout(gtx, halfWidthInt, s.Min, s.Max)
+	thumbPos := halfWidth + s.Float.Pos()
+	st.Pop()
+
+	color := s.Color
+	if gtx.Queue == nil {
+		color = mulAlpha(color, 150)
+	}
+
+	// Draw track before thumb.
+	st = op.Push(gtx.Ops)
+	track := f32.Rectangle{
+		Min: f32.Point{
+			X: halfWidth,
+			Y: halfWidth - trackWidth/2,
+		},
+		Max: f32.Point{
+			X: thumbPos,
+			Y: halfWidth + trackWidth/2,
+		},
+	}
+	clip.Rect{Rect: track}.Op(gtx.Ops).Add(gtx.Ops)
+	paint.ColorOp{Color: color}.Add(gtx.Ops)
+	paint.PaintOp{Rect: track}.Add(gtx.Ops)
+	st.Pop()
+
+	// Draw track after thumb.
+	st = op.Push(gtx.Ops)
+	track.Min.X = thumbPos
+	track.Max.X = float32(size.X) - halfWidth
+	clip.Rect{Rect: track}.Op(gtx.Ops).Add(gtx.Ops)
+	paint.ColorOp{Color: mulAlpha(color, 96)}.Add(gtx.Ops)
+	paint.PaintOp{Rect: track}.Add(gtx.Ops)
+	st.Pop()
+
+	// Draw thumb.
+	st = op.Push(gtx.Ops)
+	thumb := f32.Rectangle{
+		Min: f32.Point{
+			X: thumbPos - thumbRadius,
+			Y: halfWidth - thumbRadius,
+		},
+		Max: f32.Point{
+			X: thumbPos + thumbRadius,
+			Y: halfWidth + thumbRadius,
+		},
+	}
+	rr := thumbRadius
+	clip.Rect{
+		Rect: thumb,
+		NE:   rr, NW: rr, SE: rr, SW: rr,
+	}.Op(gtx.Ops).Add(gtx.Ops)
+	paint.ColorOp{Color: color}.Add(gtx.Ops)
+	paint.PaintOp{Rect: thumb}.Add(gtx.Ops)
+	st.Pop()
+
+	return layout.Dimensions{Size: size}
+}