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/sundial.go

@@ -0,0 +1,76 @@
+package datetime
+
+import (
+	"fmt"
+	"log/slog"
+	"math"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/icon"
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type SunDialOptions struct {
+	Disabled bool
+}
+
+type SunDialResult struct {
+	Element *ui.Element
+	Changed bool
+}
+
+// Dial size in dots: the arc's middle, radius and box.
+const dialW, dialH, dialR = 96, 56, 40
+
+// SunDial arcs the sun or moon; a drag sets *hour.
+func SunDial(c *ui.Context, text string, hour *int, o SunDialOptions) SunDialResult {
+	k := pixel.K(c)
+	if *hour < 0 || *hour > 23 {
+		panic(fmt.Sprintf("datetime: SunDial hour %d outside 0–23", *hour))
+	}
+	old := *hour
+	shell, base, st := pixel.Shell(c, func() *ui.Element {
+		return ui.Box(c).Focusable().Role(ui.RoleSlider).Label(text).Disabled(o.Disabled)
+	})
+	if base.Shortcut(0, ui.KeyLeft) {
+		*hour = (*hour + 23) % 24
+	}
+	if base.Shortcut(0, ui.KeyRight) {
+		*hour = (*hour + 1) % 24
+	}
+	// The width spans the whole day, midnight to midnight.
+	if _, _, held := base.Dragged(); held && !st.Disabled && !pixel.Current(c).Inert {
+		x, _, _ := base.PointerPosition()
+		*hour = max(0, min(23, int(x/k.D(dialW)*24)))
+	}
+	h := *hour
+	label := fmt.Sprintf("%02d:00", h)
+	base.Description(label)
+	day := h >= 6 && h < 18
+	shell.Size(k.D(dialW), k.D(dialH)).Draw(func(p *ui.Painter, r ui.Rect) {
+		g := k.Canvas(p, r)
+		sky, body := pixel.Lit, icon.Sun
+		if !day {
+			sky, body = pixel.Shade, icon.Moon
+		}
+		g.Frame(0, 0, g.W, g.H, pixel.Sunken, sky)
+		cx, cy := dialW/2, dialH-6
+		g.HLine(2, cy, dialW-4, pixel.Edge)
+		for i := 0; i <= 48; i += 2 {
+			a := math.Pi * float64(i) / 48
+			g.Dot(cx+int(math.Round(dialR*math.Cos(a))), cy-int(math.Round(dialR*math.Sin(a))), pixel.Faint)
+		}
+		t := float64((h+18)%12) / 12
+		a := math.Pi * (1 - t)
+		x, y := cx+int(math.Round(dialR*math.Cos(a))), cy-int(math.Round(dialR*math.Sin(a)))
+		g.Sprite(x-body.W/2, y-body.H/2, body, 0, pixel.Ink, 1)
+		g.Micro(3, 3, label, pixel.Ink, 1)
+		g.Finish(st)
+	})
+	res := SunDialResult{Element: shell, Changed: *hour != old}
+	if res.Changed {
+		slog.Debug("8bit: sundial", "label", text, "hour", *hour)
+	}
+	return res
+}