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/codeblock.go

@@ -0,0 +1,65 @@
+package code
+
+import (
+	"log/slog"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/input"
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/layout"
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type CodeBlockOptions struct {
+	Disabled bool
+}
+
+type CodeBlockResult struct {
+	Element *ui.Element
+	Copied  bool
+}
+
+type copiedKey struct{}
+
+// CodeBlock colors Go-like source by slot, numbers lines, copies.
+func CodeBlock(c *ui.Context, text, src string, o CodeBlockOptions) CodeBlockResult {
+	k := pixel.K(c)
+	src = tidy(src)
+	lines, slots := strings.Split(src, "\n"), paint(src)
+	gutter := pixel.Measure(strconv.Itoa(len(lines))) + 6
+	var res CodeBlockResult
+	res.Element = layout.Panel(c, layout.PanelOptions{Style: pixel.Sunken, Fill: pixel.Well, Padding: 3}, func() {
+		ui.Row(c).FillWidth().AlignItems(ui.Center).Children(func() {
+			pixel.Text(c, text, pixel.TextOptions{Slot: pixel.Faint}).Grow(1)
+			e := ui.Box(c)
+			at := ui.Local(e, copiedKey{}, func() time.Time { return time.Time{} })
+			// The button says COPIED! for two seconds.
+			label := k.Msg("copy")
+			if k.Since(c, *at, 1, 2) < 2 {
+				label = k.Msg("copied")
+			}
+			e.Children(func() {
+				if input.Button(c, label, input.ButtonOptions{Size: input.Small, Disabled: o.Disabled}).Clicked {
+					c.WriteClipboard(src)
+					*at, res.Copied = k.Now(), true
+					slog.Debug("8bit: code block copied", "label", text, "lines", len(lines))
+				}
+			})
+		})
+		off := 0
+		for i, l := range lines {
+			from := off
+			off += len(l) + 1
+			ui.Box(c).Size(k.D(gutter+pixel.Measure(l)), k.D(pixel.LineHeight)).Role(ui.RoleText).Label(l).Draw(func(p *ui.Painter, r ui.Rect) {
+				g := k.Canvas(p, r)
+				n := strconv.Itoa(i + 1)
+				g.Text(gutter-6-pixel.Measure(n), 0, n, pixel.Faint, 1)
+				colored(g, gutter, 0, l, slots[from:from+len(l)])
+			})
+		}
+	})
+	return res
+}