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/paletteeditor.go

@@ -0,0 +1,105 @@
+package code
+
+import (
+	"fmt"
+	"log/slog"
+	"math"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/input"
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type PaletteEditorOptions struct {
+	Disabled bool
+}
+
+type PaletteEditorResult struct {
+	Element *ui.Element
+	Changed bool
+}
+
+type tintKey struct{}
+
+// PaletteEditor sets *pal in channel levels; a preview follows.
+func PaletteEditor(c *ui.Context, text string, pal *pixel.Palette, o PaletteEditorOptions) PaletteEditorResult {
+	k := pixel.K(c)
+	if pal == nil {
+		panic("code: PaletteEditor needs a palette")
+	}
+	// Inside the scope everything draws in the edited colors.
+	in := pixel.Current(c)
+	in.Palette = pal
+	var res PaletteEditorResult
+	res.Element = ui.Row(c).Gap(k.D(8)).AlignItems(ui.Start)
+	sel := ui.Local(res.Element, tintKey{}, func() int { return int(pixel.Accent) })
+	res.Element.Children(func() {
+		ui.Column(c).Gap(k.D(4)).Children(func() {
+			pixel.Scope(c, in, func() {
+				// Paint runs after the scope: keep its kit now.
+				sk := pixel.K(c)
+				shell, base, st, _ := pixel.Pad(c, text, 8, int(pixel.Slots), 14, 14, sel, o.Disabled)
+				base.Description(fmt.Sprintf("%v, %s", pixel.Slot(*sel), hex(pal.Colors[*sel])))
+				at := *sel
+				shell.Draw(func(p *ui.Painter, r ui.Rect) {
+					g := sk.Canvas(p, r)
+					for s := range int(pixel.Slots) {
+						x, y := s%8*14, s/8*14
+						if s == at {
+							g.Rect(x, y, 14, 14, pixel.Accent)
+						}
+						g.Frame(x+1, y+1, 12, 12, pixel.Flat, pixel.Slot(s))
+					}
+					g.Finish(st)
+				})
+			})
+			col := &pal.Colors[*sel]
+			pixel.Text(c, fmt.Sprintf("%v %s", pixel.Slot(*sel), hex(*col)), pixel.TextOptions{Slot: pixel.Faint})
+			for _, ch := range []struct {
+				name string
+				v    *uint8
+			}{{"R", &col.R}, {"G", &col.G}, {"B", &col.B}} {
+				// Levels 0–15, each worth 17.
+				level := math.Round(float64(*ch.v) / 17)
+				ui.Row(c).Gap(k.D(4)).AlignItems(ui.Center).Children(func() {
+					// Drawn, not named: the slider carries the name.
+					ui.Box(c).Size(k.D(pixel.Measure(ch.name)), k.D(pixel.LineHeight)).Draw(func(p *ui.Painter, r ui.Rect) {
+						k.Canvas(p, r).Text(0, 0, ch.name, pixel.Faint, 1)
+					})
+					if input.StepSlider(c, ch.name, &level, input.StepSliderOptions{Max: 15, Step: 1, Width: 96, Disabled: o.Disabled}).Changed {
+						*ch.v, res.Changed = uint8(level)*17, true
+					}
+				})
+			}
+		})
+		pixel.Scope(c, in, func() { preview(c, k.Msg("preview")) })
+	})
+	if res.Changed {
+		slog.Debug("8bit: palette editor", "label", text, "slot", pixel.Slot(*sel), "color", hex(pal.Colors[*sel]))
+	}
+	return res
+}
+
+// preview is a small window drawn in the edited colors.
+func preview(c *ui.Context, text string) {
+	k := pixel.K(c)
+	ui.Box(c).Size(k.D(112), k.D(84)).Role(ui.RoleImage).Label(text).Draw(func(p *ui.Painter, r ui.Rect) {
+		g := k.Canvas(p, r)
+		g.Rect(0, 0, g.W, g.H, pixel.Back)
+		g.Frame(0, 0, 112, 84, pixel.Window, pixel.Face)
+		g.Rect(3, 3, 106, 12, pixel.Accent)
+		g.Text(6, 3, "HELLO!", pixel.AccentInk, 1)
+		g.Text(6, 18, "PRESS START", pixel.Ink, 1)
+		g.Text(6, 30, "HI 9999", pixel.Faint, 1)
+		g.Frame(6, 44, 46, 14, pixel.Raised, pixel.Face)
+		g.Text(12, 45, "OK", pixel.Ink, 1)
+		g.Frame(58, 44, 46, 14, pixel.Sunken, pixel.Well)
+		for i, s := range []pixel.Slot{pixel.Good, pixel.Warn, pixel.Bad, pixel.Info, pixel.Magic, pixel.AccentLit} {
+			g.Rect(6+i*17, 66, 15, 10, s)
+		}
+	})
+}
+
+// hex prints a color as #RRGGBB.
+func hex(col ui.Color) string { return fmt.Sprintf("#%02X%02X%02X", col.R, col.G, col.B) }