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/heatmap.go

@@ -0,0 +1,72 @@
+package chart
+
+import (
+	"fmt"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type HeatmapOptions struct {
+	// Cell is a cell's least side, zero for 10.
+	Cell int
+	// Low and High end the dither; zeros mean Well, Bad.
+	Low, High pixel.Slot
+}
+
+// Heatmap shades cells by dither level between two slots.
+func Heatmap(c *ui.Context, text string, rows, cols []string, values [][]float64, o HeatmapOptions) *ui.Element {
+	k := pixel.K(c)
+	if len(values) != len(rows) {
+		panic(fmt.Sprintf("chart: Heatmap has %d rows of values for %d rows", len(values), len(rows)))
+	}
+	for i, r := range values {
+		if len(r) != len(cols) {
+			panic(fmt.Sprintf("chart: Heatmap row %q has %d values for %d columns", rows[i], len(r), len(cols)))
+		}
+	}
+	cell := pixel.Or("Heatmap Cell", o.Cell, 10)
+	low, high := o.Low, o.High
+	if low == 0 && high == 0 {
+		low, high = pixel.Well, pixel.Bad
+	}
+	lo, hi := span(values...)
+	if hi == lo {
+		hi = lo + 1
+	}
+	rs, cs := small(rows...), small(cols...)
+	gutter := 0
+	for _, r := range rows {
+		gutter = max(gutter, markW(r, rs)+3)
+	}
+	// Cells grow to fit their labels.
+	cw, ch := cell, max(cell, inkH(rs)+2)
+	for _, col := range cols {
+		cw = max(cw, markW(col, cs)+3)
+	}
+	head := labelH(cols)
+	w, h := gutter+len(cols)*cw, head+len(rows)*ch
+	return ui.Box(c).Size(k.D(w), k.D(h)).Role(ui.RoleImage).Label(text).Description(readSeries(cols, grid(rows, values))).Draw(func(p *ui.Painter, r ui.Rect) {
+		g := k.Canvas(p, r)
+		for j, col := range cols {
+			mark(g, gutter+j*cw+(cw-markW(col, cs))/2, 1, col, cs, pixel.Faint)
+		}
+		for i, row := range values {
+			mark(g, 0, head+i*ch+(ch-1-inkH(rs))/2, rows[i], rs, pixel.Faint)
+			for j, v := range row {
+				level := int((v - lo) / (hi - lo) * 16)
+				g.Dither(gutter+j*cw, head+i*ch, cw-1, ch-1, low, high, level)
+			}
+		}
+	})
+}
+
+// grid names each row of values as a series.
+func grid(rows []string, values [][]float64) []Series {
+	out := make([]Series, len(rows))
+	for i, r := range rows {
+		out[i] = Series{Name: r, Values: values[i]}
+	}
+	return out
+}