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/code.go

@@ -0,0 +1,92 @@
+// Package code shows, runs and debugs programs and their data.
+package code
+
+import (
+	"go/scanner"
+	"go/token"
+	"strings"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+var (
+	builtins = set("any bool byte comparable complex64 complex128 error float32 float64 int int8 int16 int32 int64 rune string " +
+		"uint uint8 uint16 uint32 uint64 uintptr append cap clear close complex copy delete imag len make max min new panic print println real recover")
+	constants = set("true false nil iota")
+)
+
+func set(words string) map[string]bool {
+	m := map[string]bool{}
+	for _, w := range strings.Fields(words) {
+		m[w] = true
+	}
+	return m
+}
+
+// tidy drops carriage returns and turns tabs into four spaces.
+func tidy(src string) string {
+	src = strings.ReplaceAll(src, "\r", "")
+	return strings.TrimRight(strings.ReplaceAll(src, "\t", "    "), "\n")
+}
+
+// paint is the slot of every byte of Go-like source.
+func paint(src string) []pixel.Slot {
+	slots := make([]pixel.Slot, len(src))
+	fs := token.NewFileSet()
+	f := fs.AddFile("", -1, len(src))
+	var s scanner.Scanner
+	s.Init(f, []byte(src), nil, scanner.ScanComments)
+	for {
+		pos, tok, lit := s.Scan()
+		if tok == token.EOF {
+			return slots
+		}
+		n := len(lit)
+		if n == 0 {
+			n = len(tok.String())
+		}
+		var slot pixel.Slot
+		switch {
+		case tok == token.COMMENT:
+			slot = pixel.Faint
+		case tok == token.STRING || tok == token.CHAR:
+			slot = pixel.Good
+		case tok == token.INT || tok == token.FLOAT || tok == token.IMAG:
+			slot = pixel.Warn
+		case tok.IsKeyword():
+			slot = pixel.Accent
+		case tok == token.IDENT && builtins[lit]:
+			slot = pixel.Info
+		case tok == token.IDENT && constants[lit]:
+			slot = pixel.Magic
+		default:
+			continue
+		}
+		off := f.Offset(pos)
+		for i := off; i < min(off+n, len(src)); i++ {
+			slots[i] = slot
+		}
+	}
+}
+
+// colored draws s in runs by slot; returns the end.
+func colored(g pixel.Canvas, x, y int, s string, slots []pixel.Slot) int {
+	for i := 0; i < len(s); {
+		j := i
+		for j < len(s) && slots[j] == slots[i] {
+			j++
+		}
+		g.Text(x, y, s[i:j], slots[i], 1)
+		x += pixel.Measure(s[i:j])
+		i = j
+	}
+	return x
+}
+
+// dark is a screen's body, light ink and dim ink.
+func dark(k pixel.Kit) (body, ink, dim pixel.Slot) {
+	if k.Palette().Night {
+		return pixel.Well, pixel.Ink, pixel.Faint
+	}
+	return pixel.Ink, pixel.Lit, pixel.Shade
+}