func (p DefaultPainter) PaintMenu(canvas widget.Canvas, st *MenuPaintState) {
	if st.Bounds.IsEmpty() {
		return
	}

	// Menu background with shadow.
	shadowRect := geometry.Rect{
		Min:	geometry.Pt(st.Bounds.Min.X+dfltShadowOffset, st.Bounds.Min.Y+dfltShadowOffset),
		Max:	geometry.Pt(st.Bounds.Max.X+dfltShadowOffset, st.Bounds.Max.Y+dfltShadowOffset),
	}
	canvas.DrawRoundRect(shadowRect, dfltShadowColor, dfltMenuRadius)
	canvas.DrawRoundRect(st.Bounds, dfltMenuBg, dfltMenuRadius)
	canvas.StrokeRoundRect(st.Bounds, dfltMenuBorder, dfltMenuRadius, dfltBorderWidth)

	// Clip to menu bounds.
	canvas.PushClip(st.Bounds)
	defer canvas.PopClip()

	// Draw items.
	y := st.Bounds.Min.Y + dfltMenuPaddingV
	for i, item := range st.Items {
		if item.IsSeparator() {
			paintSeparator(canvas, st.Bounds.Min.X, y, st.Bounds.Width(), st.SeparatorHeight)
			y += st.SeparatorHeight
			continue
		}

		itemRect := geometry.Rect{
			Min:	geometry.Pt(st.Bounds.Min.X, y),
			Max:	geometry.Pt(st.Bounds.Max.X, y+st.ItemHeight),
		}

		// Highlight.
		if i == st.HighlightedIndex && !item.Disabled {
			canvas.DrawRect(itemRect, dfltItemHover)
		}

		// Label.
		textColor := dfltItemText
		if item.Disabled {
			textColor = dfltDisabledText
		}
		labelRect := geometry.Rect{
			Min:	geometry.Pt(itemRect.Min.X+dfltMenuItemPaddingH, itemRect.Min.Y),
			Max:	geometry.Pt(itemRect.Max.X-dfltShortcutAreaWidth-dfltMenuItemPaddingH, itemRect.Max.Y),
		}
		canvas.DrawText(item.Label, labelRect, dfltFontSize, textColor, false, widget.TextAlignLeft)

		// Shortcut text or submenu arrow.
		rightRect := geometry.Rect{
			Min:	geometry.Pt(itemRect.Max.X-dfltShortcutAreaWidth, itemRect.Min.Y),
			Max:	geometry.Pt(itemRect.Max.X-dfltMenuItemPaddingH, itemRect.Max.Y),
		}
		if item.HasChildren() {
			arrowColor := dfltSubMenuArrow
			if item.Disabled {
				arrowColor = dfltDisabledText
			}
			canvas.DrawText(rightArrowStr, rightRect, dfltFontSize, arrowColor, false, widget.TextAlignRight)
		} else if item.Shortcut != "" {
			shortcutColor := dfltShortcutText
			if item.Disabled {
				shortcutColor = dfltDisabledText
			}
			canvas.DrawText(item.Shortcut, rightRect, dfltShortcutFontSize, shortcutColor, false, widget.TextAlignRight)
		}

		y += st.ItemHeight
	}
}

func (p DefaultPainter) PaintMenuBar(canvas widget.Canvas, st *MenuBarPaintState) {
	if st.Bounds.IsEmpty() {
		return
	}

	// Bar background.
	canvas.DrawRect(st.Bounds, dfltBarBg)

	// Bottom border line.
	borderRect := geometry.Rect{
		Min:	geometry.Pt(st.Bounds.Min.X, st.Bounds.Max.Y-1),
		Max:	st.Bounds.Max,
	}
	canvas.DrawRect(borderRect, dfltBarBorder)

	// Draw each top-level menu label.
	for i, m := range st.Menus {
		if i >= len(st.MenuRects) {
			break
		}
		r := st.MenuRects[i]

		// Highlight background.
		switch i {
		case st.OpenIndex:
			canvas.DrawRect(r, dfltBarActiveItem)
		case st.HoveredIndex:
			canvas.DrawRect(r, dfltBarHoverItem)
		}

		// Label text.
		textColor := dfltBarTextColor
		if i == st.OpenIndex {
			textColor = dfltBarActiveText
		}
		textBounds := geometry.Rect{
			Min:	geometry.Pt(r.Min.X+dfltBarPaddingH, r.Min.Y),
			Max:	geometry.Pt(r.Max.X-dfltBarPaddingH, r.Max.Y),
		}
		canvas.DrawText(m.Label, textBounds, dfltFontSize, textColor, false, widget.TextAlignCenter)
	}
}

type MenuBarPaintState struct {
	// Bounds is the menu bar's bounds.
	Bounds	geometry.Rect

	// Menus is the list of top-level menu definitions.
	Menus	[]TopMenu

	// MenuRects contains the bounding rectangles for each top-level menu label.
	MenuRects	[]geometry.Rect

	// OpenIndex is the index of the currently open top-level menu (-1 for none).
	OpenIndex	int

	// HoveredIndex is the index of the hovered top-level menu label (-1 for none).
	HoveredIndex	int

	// Focused is true if the menu bar has keyboard focus.
	Focused	bool

	// ColorScheme provides theme-derived colors. Zero value means use defaults.
	ColorScheme	MenuColorScheme
}

type MenuPaintState struct {
	// Bounds is the menu panel's bounds in window coordinates.
	Bounds	geometry.Rect

	// Items is the list of menu items.
	Items	[]MenuItem

	// HighlightedIndex is the index of the currently highlighted item (-1 for none).
	HighlightedIndex	int

	// ItemHeight is the height of each regular item row.
	ItemHeight	float32

	// SeparatorHeight is the height of separator rows.
	SeparatorHeight	float32

	// SubMenuOpenIndex is the index of the item whose submenu is open (-1 for none).
	SubMenuOpenIndex	int

	// ColorScheme provides theme-derived colors. Zero value means use defaults.
	ColorScheme	MenuColorScheme
}

type MenuColorScheme struct {
	BarBackground		widget.Color
	BarText			widget.Color
	BarHover		widget.Color
	BarActiveText		widget.Color
	MenuBackground		widget.Color
	MenuBorder		widget.Color
	ItemText		widget.Color
	ItemHover		widget.Color
	ItemDisabledText	widget.Color
	ShortcutText		widget.Color
	SeparatorColor		widget.Color
	SubMenuArrow		widget.Color
}

type DefaultPainter struct{}

type Painter interface {
	// PaintMenuBar draws the horizontal menu bar background and top-level labels.
	PaintMenuBar(canvas widget.Canvas, state *MenuBarPaintState)

	// PaintMenu draws a popup menu panel with its items.
	PaintMenu(canvas widget.Canvas, state *MenuPaintState)
}