Add data components 151-175; clear MyGo row highlights

Lists, tables, trees, grids, inventories and records in data/.
Outline and GridView build on ui.List: ui.Outline strokes its arrows
and ui.GridView spaces and tints items. The pixel theme keeps MyGo's
row highlights clear so scrolled rows stay on whole dots; off lists
take a veil against the wheel. Adds Canvas.Silhouette, SwitchOptions
Label and exports Rarity.Slot.

data/inventory.go

@@ -0,0 +1,97 @@
+package data
+
+import (
+	"fmt"
+	"log/slog"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type InventoryOptions struct {
+	// Columns is the grid's width; zero means 6.
+	Columns  int
+	Disabled bool
+}
+
+type InventoryResult struct {
+	Element *ui.Element
+	// Swapped reports two slots traded by a drag.
+	Changed, Swapped bool
+}
+
+type bagKey struct{}
+
+// bag tracks a drag; a dead one never swaps.
+type bag struct {
+	from, over int
+	held, dead bool
+}
+
+// Inventory is a slot grid; arrows choose, drags swap.
+func Inventory(c *ui.Context, text string, items []Item, selected *int, o InventoryOptions) InventoryResult {
+	k := pixel.K(c)
+	cols := pixel.Or("Inventory Columns", o.Columns, 6)
+	off := o.Disabled || pixel.Current(c).Inert
+	if *selected < 0 || *selected >= len(items) {
+		panic(fmt.Sprintf("data: Inventory slot %d of %d", *selected, len(items)))
+	}
+	old := *selected
+	shell, base, st, _ := pixel.Pad(c, text, cols, len(items), slotSize, slotSize, selected, o.Disabled)
+	b := ui.Local(base, bagKey{}, func() bag { return bag{} })
+	res := InventoryResult{Element: shell, Changed: *selected != old}
+	px, py, _ := base.PointerPosition()
+	at := func() int {
+		col, row := int(px/k.Dot())/slotSize, int(py/k.Dot())/slotSize
+		if px < 0 || py < 0 || col >= cols || row*cols+col >= len(items) {
+			return -1
+		}
+		return row*cols + col
+	}
+	n := len(items)
+	switch _, _, pressed := base.Dragged(); {
+	case pressed && (off || b.held && max(b.from, b.over) >= n):
+		b.held, b.dead = false, true
+	case pressed && b.dead:
+	case pressed && !b.held:
+		b.held, b.from, b.over = true, at(), at()
+	case pressed:
+		b.over = at()
+	case b.held:
+		if !off && min(b.from, b.over) >= 0 && max(b.from, b.over) < n && b.from != b.over {
+			items[b.from], items[b.over] = items[b.over], items[b.from]
+			res.Swapped = true
+		}
+		b.held = false
+	default:
+		b.dead = false
+	}
+	base.Description(itemName(items[*selected]))
+	drag := -1
+	if b.held && b.over != b.from {
+		drag = b.from
+	}
+	shown := append([]Item(nil), items...)
+	shell.Draw(func(p *ui.Painter, r ui.Rect) {
+		g := k.Canvas(p, r)
+		for i, it := range shown {
+			if i == drag {
+				it = Item{}
+			}
+			slot(g, i%cols*slotSize, i/cols*slotSize, it, 0, i == *selected)
+		}
+		// The dragged item rides with the pointer.
+		if drag >= 0 && shown[drag].Sprite != nil {
+			g.Sprite(int(px/k.Dot())-6, int(py/k.Dot())-6, shown[drag].Sprite, 0, pixel.Ink, 1)
+		}
+		g.Finish(st)
+	})
+	if res.Changed {
+		slog.Debug("8bit: inventory chose", "label", text, "slot", *selected)
+	}
+	if res.Swapped {
+		slog.Debug("8bit: inventory swap", "label", text, "from", b.from, "to", b.over)
+	}
+	return res
+}