widget/material: add ProgressBar

Add progress indicator support to material widget

Signed-off-by: metaclips <utimichael9@gmail.com>

widget/material/progressbar.go

@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package material
+
+import (
+	"image"
+	"image/color"
+
+	"gioui.org/f32"
+	"gioui.org/layout"
+	"gioui.org/op/clip"
+	"gioui.org/op/paint"
+	"gioui.org/unit"
+)
+
+type ProgressBar struct {
+	Color color.RGBA
+}
+
+func (t *Theme) ProgressBar() ProgressBar {
+	return ProgressBar{
+		Color: t.Color.Primary,
+	}
+}
+
+func (b ProgressBar) Layout(gtx *layout.Context, progress int) {
+	shader := func(width float32, color color.RGBA) {
+		maxHeight := unit.Dp(4)
+		rr := float32(gtx.Px(unit.Dp(2)))
+
+		d := image.Point{X: int(width), Y: gtx.Px(maxHeight)}
+		dr := f32.Rectangle{
+			Max: f32.Point{X: float32(d.X), Y: float32(d.Y)},
+		}
+
+		clip.Rect{
+			Rect: f32.Rectangle{Max: f32.Point{X: width, Y: float32(gtx.Px(maxHeight))}},
+			NE:   rr, NW: rr, SE: rr, SW: rr,
+		}.Op(gtx.Ops).Add(gtx.Ops)
+
+		paint.ColorOp{Color: color}.Add(gtx.Ops)
+		paint.PaintOp{Rect: dr}.Add(gtx.Ops)
+
+		gtx.Dimensions = layout.Dimensions{Size: d}
+	}
+
+	if progress > 100 {
+		progress = 100
+	} else if progress < 0 {
+		progress = 0
+	}
+
+	progressBarWidth := float32(gtx.Constraints.Width.Max)
+
+	layout.Stack{Alignment: layout.W}.Layout(gtx,
+		layout.Stacked(func() {
+			// Use a transparent equivalent of progress color.
+			backgroundColor := b.Color
+			backgroundColor.A = 100
+
+			shader(progressBarWidth, backgroundColor)
+		}),
+		layout.Stacked(func() {
+			fillWidth := (progressBarWidth / 100) * float32(progress)
+			shader(fillWidth, b.Color)
+		}),
+	)
+}