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

	// Menu background.
	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 visible items.
	endIndex := st.ScrollOffset + st.VisibleCount
	if endIndex > len(st.Items) {
		endIndex = len(st.Items)
	}

	for i := st.ScrollOffset; i < endIndex; i++ {
		item := st.Items[i]
		row := i - st.ScrollOffset
		itemRect := geometry.Rect{
			Min:	geometry.Pt(st.Bounds.Min.X, st.Bounds.Min.Y+float32(row)*st.ItemHeight),
			Max:	geometry.Pt(st.Bounds.Max.X, st.Bounds.Min.Y+float32(row+1)*st.ItemHeight),
		}

		// Highlight.
		switch i {
		case st.HighlightedIndex:
			canvas.DrawRect(itemRect, dfltItemHover)
		case st.SelectedIndex:
			canvas.DrawRect(itemRect, dfltItemSelected)
		}

		// Text.
		textColor := dfltTextColor
		if item.Disabled {
			textColor = dfltDisabledFg
		}
		textRect := geometry.Rect{
			Min:	geometry.Pt(itemRect.Min.X+dfltPaddingH, itemRect.Min.Y),
			Max:	geometry.Pt(itemRect.Max.X-dfltPaddingH, itemRect.Max.Y),
		}
		canvas.DrawText(item.DisplayText(), textRect, dfltFontSize, textColor, false, dfltTextAlignLeft)
	}
}

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

	// Background.
	bg := dfltTriggerBg
	if st.Disabled {
		bg = dfltDisabledBg
	}
	canvas.DrawRoundRect(st.Bounds, bg, dfltRadius)

	// Border.
	borderColor := dfltBorder
	borderWidth := dfltBorderWidth
	if st.Focused {
		borderColor = dfltFocusBorder
		borderWidth = dfltFocusBorderWidth
	}
	if st.Disabled {
		borderColor = dfltDisabledFg
	}
	canvas.StrokeRoundRect(st.Bounds, borderColor, dfltRadius, borderWidth)

	// Text.
	textColor := dfltTextColor
	if st.IsPlaceholder {
		textColor = dfltPlaceholder
	}
	if st.Disabled {
		textColor = dfltDisabledFg
	}
	textBounds := geometry.Rect{
		Min:	geometry.Pt(st.Bounds.Min.X+dfltPaddingH, st.Bounds.Min.Y),
		Max:	geometry.Pt(st.Bounds.Max.X-dfltChevronWidth-dfltPaddingH, st.Bounds.Max.Y),
	}
	canvas.DrawText(st.SelectedText, textBounds, dfltFontSize, textColor, false, dfltTextAlignLeft)

	// Chevron indicator.
	chevronColor := dfltChevronColor
	if st.Disabled {
		chevronColor = dfltDisabledFg
	}
	chevronX := st.Bounds.Max.X - dfltChevronWidth - dfltPaddingH/2
	chevronY := st.Bounds.Center().Y
	drawChevron(canvas, geometry.Pt(chevronX, chevronY), st.Open, chevronColor)
}

type TriggerPaintState struct {
	// Bounds is the trigger widget's bounds.
	Bounds	geometry.Rect

	// SelectedText is the display text of the currently selected item,
	// or the placeholder if nothing is selected.
	SelectedText	string

	// IsPlaceholder is true if SelectedText is the placeholder (nothing selected).
	IsPlaceholder	bool

	// Open is true if the dropdown menu is currently visible.
	Open	bool

	// Focused is true if the dropdown has keyboard focus.
	Focused	bool

	// Hovered is true if the mouse is over the trigger.
	Hovered	bool

	// Disabled is true if the dropdown is disabled.
	Disabled	bool

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

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

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

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

	// SelectedIndex is the index of the currently selected item (-1 for none).
	SelectedIndex	int

	// ScrollOffset is the index of the first visible item.
	ScrollOffset	int

	// VisibleCount is the number of items visible without scrolling.
	VisibleCount	int

	// ItemHeight is the height of each item in the menu.
	ItemHeight	float32

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

type DropdownColorScheme struct {
	Background	widget.Color
	Border		widget.Color
	FocusBorder	widget.Color
	TextColor	widget.Color
	PlaceholderText	widget.Color
	DisabledBg	widget.Color
	DisabledFg	widget.Color
	MenuBg		widget.Color
	MenuBorder	widget.Color
	ItemHover	widget.Color
	ItemSelected	widget.Color
	ItemDisabled	widget.Color
	ChevronColor	widget.Color
	FocusRing	widget.Color
}

type DefaultPainter struct{}

type Painter interface {
	// PaintTrigger draws the closed dropdown trigger (shows current selection).
	PaintTrigger(canvas widget.Canvas, state *TriggerPaintState)

	// PaintMenu draws the open dropdown menu.
	PaintMenu(canvas widget.Canvas, state *MenuPaintState)
}