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/radarchart.go

@@ -0,0 +1,119 @@
+package chart
+
+import (
+	"fmt"
+	"math"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type RadarChartOptions struct {
+	// Max is the web's rim; zero takes the largest value.
+	Max float64
+	// Size is the web's width in dots; zero means 80.
+	Size int
+	Slot pixel.Slot
+}
+
+// RadarChart draws a stat polygon on a web of axes.
+func RadarChart(c *ui.Context, text string, axes []string, values []float64, o RadarChartOptions) *ui.Element {
+	k := pixel.K(c)
+	if len(axes) != len(values) || len(axes) < 3 {
+		panic(fmt.Sprintf("chart: RadarChart has %d axes for %d values", len(axes), len(values)))
+	}
+	span([]float64{o.Max})
+	lo, top := span(values)
+	if lo < 0 || o.Max < 0 || o.Max > 0 && top > o.Max {
+		panic(fmt.Sprintf("chart: RadarChart values %v–%v outside 0–%v", lo, top, o.Max))
+	}
+	if o.Max > 0 {
+		top = o.Max
+	}
+	// All zeros: any rim works; the polygon sits mid-web.
+	if top == 0 {
+		top = 1
+	}
+	n := pixel.Or("RadarChart Size", o.Size, 80)
+	sm, ink := small(axes...), pick(o.Slot, 0)
+	rad := web(axes, sm, n)
+	// point is where value v sits on axis i.
+	point := func(i int, v float64) (int, int) {
+		sin, cos := math.Sincos(2 * math.Pi * float64(i) / float64(len(axes)))
+		reach := v / top * float64(rad)
+		return n/2 + int(math.Round(reach*sin)), n/2 - int(math.Round(reach*cos))
+	}
+	return ui.Box(c).Size(k.D(n), k.D(n)).Role(ui.RoleImage).Label(text).Description(read(axes, values)).Draw(func(p *ui.Painter, r ui.Rect) {
+		g := k.Canvas(p, r)
+		for _, ring := range []float64{1.0 / 3, 2.0 / 3, 1} {
+			for i := range axes {
+				x0, y0 := point(i, ring*top)
+				x1, y1 := point((i+1)%len(axes), ring*top)
+				g.Line(x0, y0, x1, y1, pixel.Shade)
+			}
+		}
+		for i, a := range axes {
+			x, y := point(i, top)
+			g.Line(n/2, n/2, x, y, pixel.Shade)
+			lx, ly := tag(i, len(axes), rad, markW(a, sm), inkH(sm), n)
+			mark(g, lx, ly, a, sm, pixel.Faint)
+		}
+		for i, v := range values {
+			x0, y0 := point(i, v)
+			x1, y1 := point((i+1)%len(values), values[(i+1)%len(values)])
+			g.Line(x0, y0, x1, y1, ink)
+		}
+		for i, v := range values {
+			x, y := point(i, v)
+			g.Rect(x-1, y-1, 3, 3, ink)
+		}
+	})
+}
+
+// gap is the room between the rim and a label.
+const gap = 3
+
+// lean is -1, 0 or 1: a label's side.
+func lean(v float64) float64 {
+	switch {
+	case v > 0.3:
+		return 1
+	case v < -0.3:
+		return -1
+	}
+	return 0
+}
+
+// web is the largest rim keeping every label inside.
+func web(axes []string, sm bool, n int) int {
+	rad := float64(n/2 - 1)
+	for i, a := range axes {
+		sin, cos := math.Sincos(2 * math.Pi * float64(i) / float64(len(axes)))
+		w, h := float64(markW(a, sm)), float64(inkH(sm))
+		// A leaning label reaches its whole size out; others half.
+		ex, ey := w/2*(1+math.Abs(lean(sin))), h/2*(1+math.Abs(lean(cos)))
+		if ex > float64(n)/2 || ey > float64(n)/2 {
+			rad = 0
+		}
+		if s := math.Abs(sin); s > 1e-9 {
+			rad = min(rad, (float64(n/2)-ex)/s-gap)
+		}
+		if c := math.Abs(cos); c > 1e-9 {
+			rad = min(rad, (float64(n/2)-ey)/c-gap)
+		}
+	}
+	if rad < 4 {
+		panic(fmt.Sprintf("chart: RadarChart Size %d leaves no room inside its labels", n))
+	}
+	return int(rad)
+}
+
+// tag is the top left of axis i's label.
+func tag(i, count, rad, w, h, n int) (int, int) {
+	sin, cos := math.Sincos(2 * math.Pi * float64(i) / float64(count))
+	ax, ay := float64(n)/2+float64(rad+gap)*sin, float64(n)/2-float64(rad+gap)*cos
+	x := ax - float64(w)/2*(1-lean(sin))
+	y := ay - float64(h)/2*(1+lean(cos))
+	return max(0, min(n-w, int(math.Round(x)))), max(0, min(n-h, int(math.Round(y))))
+}