Add code components 366-385; ScrollArea Follow, editor sync

A terminal with history, a Go-colored code block, a log viewer that
follows, a hex viewer, a memory map, a JSON tree, a line diff, a GAME
OVER crash screen, an FPS meter, profiler bars, breakpoints,
variables, command history, a shortcut list, a debug grid, a pixel
editor that exports string art, a palette editor, a sprite sheet, a
glyph map and a 6502 register view.

layout.ScrollArea takes Follow, and ChatLog now uses it. data.TreeNode
takes a Value drawn in its Slot. pixel gains Has, and Sprite.Art
writes MustSprite art. pixel.Editor takes the caller's value at each
input event, so a value changed between frames is never typed onto.

code/profilerbars.go

@@ -0,0 +1,70 @@
+package code
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+// Span is timed work, starting inside its parent's time.
+type Span struct {
+	Name          string
+	Start, Length time.Duration
+	Children      []Span
+}
+
+type ProfilerBarsOptions struct {
+	// Width is in dots; zero means 240.
+	Width int
+}
+
+var depths = []pixel.Slot{pixel.Accent, pixel.Info, pixel.Good, pixel.Warn, pixel.Magic}
+
+// ProfilerBars stacks spans under their parents, each bar its time.
+func ProfilerBars(c *ui.Context, text string, root Span, o ProfilerBarsOptions) *ui.Element {
+	k := pixel.K(c)
+	w := pixel.Or("ProfilerBars Width", o.Width, 240)
+	if root.Length <= 0 {
+		panic(fmt.Sprintf("code: ProfilerBars root %q lasts %v", root.Name, root.Length))
+	}
+	var said []string
+	rows := check(root, &said)
+	x := func(d time.Duration) int { return int(int64(w) * int64(d-root.Start) / int64(root.Length)) }
+	return ui.Box(c).Size(k.D(w), k.D(rows*pixel.LineHeight)).Role(ui.RoleImage).Label(text).Description(strings.Join(said, "; ")).Draw(func(p *ui.Painter, r ui.Rect) {
+		g := k.Canvas(p, r)
+		var bar func(s Span, depth int)
+		bar = func(s Span, depth int) {
+			x0, y := x(s.Start), depth*pixel.LineHeight
+			bw := max(1, x(s.Start+s.Length)-x0)
+			g.Rect(x0, y+1, bw, pixel.LineHeight-2, depths[depth%len(depths)])
+			// Names show where they fit, times when they also fit.
+			for _, s := range []string{fmt.Sprintf("%s %.1fms", s.Name, ms(s.Length)), s.Name} {
+				if pixel.Measure(s)+4 <= bw {
+					g.Text(x0+2, y, s, pixel.AccentInk, 1)
+					break
+				}
+			}
+			for _, ch := range s.Children {
+				bar(ch, depth+1)
+			}
+		}
+		bar(root, 0)
+	})
+}
+
+// check counts rows; a child outside its parent panics.
+func check(s Span, said *[]string) int {
+	*said = append(*said, fmt.Sprintf("%s %.1f ms", s.Name, ms(s.Length)))
+	rows := 1
+	for _, ch := range s.Children {
+		if ch.Length < 0 || ch.Start < s.Start || ch.Start+ch.Length > s.Start+s.Length {
+			panic(fmt.Sprintf("code: ProfilerBars span %q is outside %q", ch.Name, s.Name))
+		}
+		rows = max(rows, 1+check(ch, said))
+	}
+	return rows
+}