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.

chat/chatlog.go

@@ -1,8 +1,6 @@
 package chat
 
 import (
-	"math"
-
 	"github.com/egoist/mygo/ui"
 
 	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/layout"
@@ -16,35 +14,14 @@ type ChatLogOptions struct {
 
 type logKey struct{}
 
-// logState is the scroll and the end it last reached.
-type logState struct {
-	scroll ui.ScrollState
-	end    float32
-}
-
 // ChatLog scrolls messages and follows the end while there.
 func ChatLog(c *ui.Context, text string, o ChatLogOptions, content func()) *ui.Element {
 	k := pixel.K(c)
 	w, h := pixel.Or("ChatLog Width", o.Width, 220), pixel.Or("ChatLog Height", o.Height, 140)
 	box := ui.Box(c).Size(k.D(w), k.D(h))
-	st := ui.Local(box, logKey{}, func() logState { return logState{scroll: ui.ScrollState{Y: math.MaxFloat32}} })
-	// Content grew under a view at its old end: follow.
-	grew := func() bool { return st.scroll.MaxY > st.end && st.scroll.Y >= st.end }
-	// Inert freezes the view; the end waits until it wakes.
-	frozen := pixel.Current(c).Inert
-	if !frozen {
-		if grew() {
-			st.scroll.Y = st.scroll.MaxY
-		}
-		st.end = st.scroll.MaxY
-	}
-	return box.Draw(func(p *ui.Painter, r ui.Rect) {
-		// Layout has just measured the content; follow it next frame.
-		if !frozen && grew() {
-			c.Invalidate()
-		}
-	}).Children(func() {
-		layout.ScrollArea(c, &st.scroll, layout.ScrollAreaOptions{Label: text}, func() {
+	s := ui.Local(box, logKey{}, func() ui.ScrollState { return ui.ScrollState{} })
+	return box.Children(func() {
+		layout.ScrollArea(c, s, layout.ScrollAreaOptions{Label: text, Follow: true}, func() {
 			ui.Column(c).FillWidth().Padding(k.D(4)).Gap(k.D(4)).Children(content)
 		}).Element.Fill()
 	})