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/barchart.go

@@ -0,0 +1,73 @@
+package chart
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type BarChartOptions struct {
+	// Width and Height are dots; zeros mean 160 by 80.
+	Width, Height int
+	// Slot fills the bars; zero means Accent.
+	Slot pixel.Slot
+}
+
+// BarChart stands bars on micro-font axes; hover reads a value.
+func BarChart(c *ui.Context, text string, labels []string, values []float64, o BarChartOptions) *ui.Element {
+	k := pixel.K(c)
+	if len(labels) != len(values) || len(values) == 0 {
+		panic(fmt.Sprintf("chart: BarChart has %d labels for %d values", len(labels), len(values)))
+	}
+	w, h := size("BarChart", o.Width, o.Height, 160, 80)
+	lo, hi := span(values)
+	p := fit(min(0, lo), max(0, hi), w, h, labels)
+	e := ui.Box(c).Size(k.D(w), k.D(h)).Role(ui.RoleImage).Label(text).Description(read(labels, values))
+	hover := -1
+	if x, y, over := e.PointerPosition(); over {
+		if dx := int(x/k.Dot()) - p.x; dx >= 0 && dx < p.w && int(y/k.Dot()) < p.y+p.h {
+			hover = dx * len(values) / p.w
+		}
+	}
+	ink := pick(o.Slot, 0)
+	return e.Draw(func(pt *ui.Painter, r ui.Rect) {
+		g := k.Canvas(pt, r)
+		p.grid(g, labels)
+		share := p.w / len(values)
+		bw, zero := max(1, share*2/3), p.at(0)
+		for i, v := range values {
+			x, top := p.slot(i, len(values))-bw/2, p.at(v)
+			g.Rect(x, min(top, zero), bw, max(1, abs(zero-top)), ink)
+		}
+		if hover >= 0 {
+			readout(g, p.slot(hover, len(values)), p.at(values[hover]), num(values[hover]), w)
+		}
+	})
+}
+
+// readout boxes s above x, y, kept inside w dots.
+func readout(g pixel.Canvas, x, y int, s string, w int) {
+	bw := tinyW(s) + 4
+	bx, by := max(0, min(w-bw, x-bw/2)), max(0, y-11)
+	g.Frame(bx, by, bw, 9, pixel.Flat, pixel.Lit)
+	tiny(g, bx+2, by+2, s, pixel.Ink)
+}
+
+// read lists values for assistive technology: "A 3, B 5".
+func read(labels []string, values []float64) string {
+	parts := make([]string, len(values))
+	for i, v := range values {
+		parts[i] = labels[i] + " " + num(v)
+	}
+	return strings.Join(parts, ", ")
+}
+
+func abs(n int) int {
+	if n < 0 {
+		return -n
+	}
+	return n
+}