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/jsontree.go

@@ -0,0 +1,77 @@
+package code
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/data"
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type JSONTreeOptions struct {
+	// Width is in dots; zero means 200.
+	Width    int
+	Disabled bool
+}
+
+type JSONTreeResult = data.TreeResult
+
+// JSONTree shows JSON as a tree; values colored by type.
+func JSONTree(c *ui.Context, text, doc string, selected *string, o JSONTreeOptions) JSONTreeResult {
+	dec := json.NewDecoder(strings.NewReader(doc))
+	dec.UseNumber()
+	root := node(dec, "")
+	if _, err := dec.Token(); err != io.EOF {
+		panic(fmt.Sprintf("code: JSONTree: after the value, %v", err))
+	}
+	// An empty container or lone value is its own row.
+	roots := root.Children
+	if len(roots) == 0 {
+		roots = []data.TreeNode{root}
+	}
+	return data.Tree(c, text, roots, selected, data.TreeOptions{Width: pixel.Or("JSONTree Width", o.Width, 200), Disabled: o.Disabled})
+}
+
+// node reads the next value under label; bad JSON panics.
+func node(dec *json.Decoder, label string) data.TreeNode {
+	tok, err := dec.Token()
+	if err != nil {
+		panic(fmt.Sprintf("code: JSONTree: %v", err))
+	}
+	n := data.TreeNode{Label: label, Slot: pixel.Faint}
+	switch v := tok.(type) {
+	case json.Delim:
+		end := "]"
+		if v == '{' {
+			end = "}"
+		}
+		for i := 0; dec.More(); i++ {
+			key := strconv.Itoa(i)
+			if v == '{' {
+				t, _ := dec.Token()
+				key = t.(string)
+			}
+			n.Children = append(n.Children, node(dec, key))
+		}
+		dec.Token()
+		n.Value = fmt.Sprintf("%c%d%s", v, len(n.Children), end)
+		// An empty object or array still opens nothing.
+		if n.Children == nil {
+			n.Children = []data.TreeNode{}
+		}
+	case string:
+		n.Value, n.Slot = strconv.QuoteToGraphic(v), pixel.Good
+	case json.Number:
+		n.Value, n.Slot = v.String(), pixel.Warn
+	case bool:
+		n.Value, n.Slot = strconv.FormatBool(v), pixel.Info
+	case nil:
+		n.Value = "null"
+	}
+	return n
+}