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/pyramid.go

@@ -0,0 +1,48 @@
+package chart
+
+import (
+	"fmt"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type PyramidOptions struct {
+	// Width is in dots, zero means 200; rows are lines.
+	Width int
+}
+
+// Pyramid sets two series back to back by group.
+func Pyramid(c *ui.Context, text string, groups []string, left, right Series, o PyramidOptions) *ui.Element {
+	k := pixel.K(c)
+	if len(left.Values) != len(groups) || len(right.Values) != len(groups) {
+		panic(fmt.Sprintf("chart: Pyramid has %d groups for %d and %d values", len(groups), len(left.Values), len(right.Values)))
+	}
+	w := pixel.Or("Pyramid Width", o.Width, 200)
+	lo, hi := span(left.Values, right.Values)
+	if lo < 0 {
+		panic(fmt.Sprintf("chart: Pyramid value %v is negative", lo))
+	}
+	mid := 0
+	for _, g := range groups {
+		mid = max(mid, pixel.Measure(g)+12)
+	}
+	lslot, rslot := pick(left.Slot, 1), pick(right.Slot, 0)
+	head := pixel.LineHeight
+	return ui.Box(c).Size(k.D(w), k.D(head+len(groups)*pixel.LineHeight)).Role(ui.RoleImage).Label(text).
+		Description(left.Name + ": " + read(groups, left.Values) + "; " + right.Name + ": " + read(groups, right.Values)).Draw(func(p *ui.Painter, r ui.Rect) {
+		g := k.Canvas(p, r)
+		reach := (w - mid) / 2
+		cx := reach + mid/2
+		g.Text(0, 0, left.Name, lslot, 1)
+		g.Text(w-pixel.Measure(right.Name), 0, right.Name, rslot, 1)
+		for i, name := range groups {
+			y := head + i*pixel.LineHeight
+			g.Text(cx-pixel.Measure(name)/2, y, name, pixel.Faint, 1)
+			lw, rw := int(part(left.Values[i], hi)*float64(reach)), int(part(right.Values[i], hi)*float64(reach))
+			g.Rect(reach-lw, y+4, lw, pixel.LineHeight-8, lslot)
+			g.Rect(reach+mid, y+4, rw, pixel.LineHeight-8, rslot)
+		}
+	})
+}