Add chart components 216-245; step-aware ticks, font-aware labels

Bars, lines, areas, pies, donuts, radar, histogram, scatter, bubbles,
heatmaps, gauge, bullet, funnel, waterfall, treemap, candles, box
plots, steps, rings, legend, axis, crosshair, polar area, pyramid,
spectrum bars and win-loss strips, each drawn dot by dot. Ticks follow
1-2-5 steps and print as precisely as their step needs; a label row
uses micro letters or the pixel font as a whole. Descriptions carry the
data in numbers. Bad data panics.

chart/legend.go

@@ -0,0 +1,54 @@
+package chart
+
+import (
+	"fmt"
+	"log/slog"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type LegendOptions struct {
+	Disabled bool
+}
+
+type LegendResult struct {
+	Element *ui.Element
+	Changed bool
+}
+
+// Legend names series by swatch; clicks hide or show one.
+func Legend(c *ui.Context, text string, series []Series, hidden []bool, o LegendOptions) LegendResult {
+	k := pixel.K(c)
+	if len(hidden) != len(series) {
+		panic(fmt.Sprintf("chart: Legend has %d series and %d hidden flags", len(series), len(hidden)))
+	}
+	row := ui.Row(c).Gap(k.D(8)).FocusGroup(ui.Horizontal).Role(ui.RoleGroup).Label(text)
+	res := LegendResult{Element: row}
+	row.Children(func() {
+		for i, s := range series {
+			shown := !hidden[i]
+			shell, base, st := pixel.Shell(c, func() *ui.Element { return ui.ToggleBase(c, &shown).Label(s.Name).Disabled(o.Disabled) })
+			if base.Changed() {
+				hidden[i], res.Changed = !shown, true
+				slog.Debug("8bit: legend", "label", text, "series", s.Name, "shown", shown)
+			}
+			ink := pick(s.Slot, i)
+			shell.Size(k.D(10+pixel.Measure(s.Name)), k.D(pixel.LineHeight)).Draw(func(p *ui.Painter, r ui.Rect) {
+				g := k.Canvas(p, r)
+				name := pixel.Ink
+				if shown {
+					g.Rect(0, 5, 6, 6, ink)
+				} else {
+					g.Rect(0, 5, 6, 6, pixel.Edge)
+					g.Rect(1, 6, 4, 4, pixel.Well)
+					name = pixel.Faint
+				}
+				g.Text(10, 0, s.Name, name, 1)
+				g.Finish(st)
+			})
+		}
+	})
+	return res
+}