Add datetime components 196-215; Kit.At; inert stepper arrows

Calendars, date and time inputs, pickers, clocks, timers, a sun dial,
a season wheel, an agenda and a day schedule. Kit.At rebuilds at a
moment (relative times, midnight). Stepper and NumberInput arrows stop
under Inert. DateInput parks a popup focus as its own.

datetime/stopwatch.go

@@ -0,0 +1,82 @@
+package datetime
+
+import (
+	"fmt"
+	"log/slog"
+	"time"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/input"
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type StopwatchOptions struct {
+	Disabled bool
+}
+
+type StopwatchResult struct {
+	Element                         *ui.Element
+	Started, Stopped, Lapped, Reset bool
+}
+
+type watchKey struct{}
+
+// watch is time banked, since when it runs, and laps.
+type watch struct {
+	banked time.Duration
+	since  time.Time
+	laps   []time.Duration
+}
+
+// tenths prints d as MM:SS.T.
+func tenths(d time.Duration) string {
+	return fmt.Sprintf("%s.%d", clock(d), int(d/(100*time.Millisecond))%10)
+}
+
+// Stopwatch times with START, STOP, LAP, RESET; laps below.
+func Stopwatch(c *ui.Context, text string, o StopwatchOptions) StopwatchResult {
+	k := pixel.K(c)
+	col := ui.Column(c).Gap(k.D(4)).Role(ui.RoleGroup).Label(text)
+	w := ui.Local(col, watchKey{}, func() watch { return watch{} })
+	now := k.Now()
+	running := !w.since.IsZero()
+	elapsed := w.banked
+	if running {
+		elapsed += now.Sub(w.since)
+		k.Tick(c, 10)
+	}
+	res := StopwatchResult{Element: col}
+	col.Children(func() {
+		s := tenths(elapsed)
+		ui.Box(c).Size(k.D(pixel.Measure(s)*2), k.D(pixel.LineHeight*2)).Role(ui.RoleText).Label(s).Draw(func(p *ui.Painter, r ui.Rect) {
+			k.Canvas(p, r).Text(0, 0, s, pixel.Ink, 2)
+		})
+		ui.Row(c).Gap(k.D(4)).Children(func() {
+			toggle := k.Msg("start")
+			if running {
+				toggle = k.Msg("stop")
+			}
+			if input.Button(c, toggle, input.ButtonOptions{Size: input.Small, Variant: input.Primary, Disabled: o.Disabled}).Clicked {
+				if running {
+					w.banked, w.since, res.Stopped = elapsed, time.Time{}, true
+				} else {
+					w.since, res.Started = now, true
+				}
+			}
+			if input.Button(c, k.Msg("lap"), input.ButtonOptions{Size: input.Small, Disabled: o.Disabled || !running}).Clicked {
+				w.laps, res.Lapped = append(w.laps, elapsed), true
+			}
+			if input.Button(c, k.Msg("reset"), input.ButtonOptions{Size: input.Small, Disabled: o.Disabled || running || elapsed == 0}).Clicked {
+				*w, res.Reset = watch{}, true
+			}
+		})
+		for i := len(w.laps) - 1; i >= max(0, len(w.laps)-5); i-- {
+			pixel.Text(c, fmt.Sprintf("%s %d  %s", k.Msg("lap"), i+1, tenths(w.laps[i])), pixel.TextOptions{Slot: pixel.Faint})
+		}
+	})
+	if res.Started || res.Stopped || res.Lapped || res.Reset {
+		slog.Debug("8bit: stopwatch", "label", text, "elapsed", elapsed, "laps", len(w.laps))
+	}
+	return res
+}