feat(tracker): implement alerts that display useful notifications / errors

In particular, we show notification after the user has copied something to clipboard (#34) and when there is a patch compile error (#38).

tracker/alert.go

@@ -0,0 +1,116 @@
+package tracker
+
+import (
+	"image/color"
+	"time"
+
+	"gioui.org/f32"
+	"gioui.org/layout"
+	"gioui.org/op"
+	"gioui.org/op/clip"
+	"gioui.org/op/paint"
+	"gioui.org/unit"
+)
+
+type Alert struct {
+	message       string
+	alertType     AlertType
+	duration      time.Duration
+	showMessage   string
+	showAlertType AlertType
+	showDuration  time.Duration
+	showTime      time.Time
+	pos           float64
+	lastUpdate    time.Time
+}
+
+type AlertType int
+
+const (
+	None AlertType = iota
+	Notify
+	Warning
+	Error
+)
+
+var alertSpeed = 150 * time.Millisecond
+var alertMargin = layout.UniformInset(unit.Dp(6))
+var alertInset = layout.UniformInset(unit.Dp(6))
+
+func (a *Alert) Update(message string, alertType AlertType, duration time.Duration) {
+	if a.alertType < alertType {
+		a.message = message
+		a.alertType = alertType
+		a.duration = duration
+	}
+}
+
+func (a *Alert) Layout(gtx C) D {
+	now := time.Now()
+	if a.alertType != None {
+		a.showMessage = a.message
+		a.showAlertType = a.alertType
+		a.showTime = now
+		a.showDuration = a.duration
+	}
+	a.alertType = None
+	var targetPos float64 = 0.0
+	if now.Sub(a.showTime) <= a.showDuration {
+		targetPos = 1.0
+	}
+	delta := float64(now.Sub(a.lastUpdate)) / float64(alertSpeed)
+	if a.pos < targetPos {
+		a.pos += delta
+		if a.pos > targetPos {
+			a.pos = targetPos
+		} else {
+			op.InvalidateOp{At: now.Add(50 * time.Millisecond)}.Add(gtx.Ops)
+		}
+	} else if a.pos > targetPos {
+		a.pos -= delta
+		if a.pos < targetPos {
+			a.pos = targetPos
+		} else {
+			op.InvalidateOp{At: now.Add(50 * time.Millisecond)}.Add(gtx.Ops)
+		}
+	}
+	a.lastUpdate = now
+	var color, textColor, shadeColor color.NRGBA
+	switch a.showAlertType {
+	case Warning:
+		color = warningColor
+		textColor = black
+	case Error:
+		color = errorColor
+		textColor = black
+	default:
+		color = popupSurfaceColor
+		textColor = white
+		shadeColor = black
+	}
+	bgWidget := func(gtx C) D {
+		paint.FillShape(gtx.Ops, color, clip.Rect{
+			Max: gtx.Constraints.Min,
+		}.Op())
+		return D{Size: gtx.Constraints.Min}
+	}
+	labelStyle := LabelStyle{Text: a.showMessage, Color: textColor, ShadeColor: shadeColor, Font: labelDefaultFont, Alignment: layout.Center, FontSize: unit.Dp(16)}
+	return alertMargin.Layout(gtx, func(gtx C) D {
+		return layout.S.Layout(gtx, func(gtx C) D {
+			defer op.Save(gtx.Ops).Load()
+			gtx.Constraints.Min.X = gtx.Constraints.Max.X
+			recording := op.Record(gtx.Ops)
+			dims := layout.Stack{Alignment: layout.Center}.Layout(gtx,
+				layout.Expanded(bgWidget),
+				layout.Stacked(func(gtx C) D {
+					return alertInset.Layout(gtx, labelStyle.Layout)
+				}),
+			)
+			macro := recording.Stop()
+			totalY := dims.Size.Y + gtx.Px(alertMargin.Bottom)
+			op.Offset(f32.Pt(0, float32((1-a.pos)*float64(totalY)))).Add((gtx.Ops))
+			macro.Add(gtx.Ops)
+			return dims
+		})
+	})
+}