func (p TreeViewPainter) PaintConnectorLines(canvas widget.Canvas, s treeview.ConnectorState) {
	if s.RowBounds.IsEmpty() || s.Depth == 0 {
		return
	}
	colors := p.effectiveColors(s.ColorScheme)
	midY := s.RowBounds.Min.Y + s.RowBounds.Height()/2

	// Vertical continuation lines for ancestors.
	for i := 0; i < len(s.ParentHasMore); i++ {
		if !s.ParentHasMore[i] {
			continue
		}
		depth := i + 1
		x := s.RowBounds.Min.X + float32(depth)*s.IndentWidth + s.IndentWidth/2
		canvas.DrawLine(
			geometry.Pt(x, s.RowBounds.Min.Y),
			geometry.Pt(x, s.RowBounds.Min.Y+s.RowBounds.Height()),
			colors.LineColor, dtTreeConnectorWidth,
		)
	}

	// Horizontal connector from parent's vertical line to this node.
	x := s.RowBounds.Min.X + float32(s.Depth)*s.IndentWidth + s.IndentWidth/2
	hEnd := s.RowBounds.Min.X + float32(s.Depth+1)*s.IndentWidth

	vEnd := midY
	if !s.IsLastChild {
		vEnd = s.RowBounds.Min.Y + s.RowBounds.Height()
	}
	canvas.DrawLine(
		geometry.Pt(x, s.RowBounds.Min.Y),
		geometry.Pt(x, vEnd),
		colors.LineColor, dtTreeConnectorWidth,
	)
	canvas.DrawLine(
		geometry.Pt(x, midY),
		geometry.Pt(hEnd, midY),
		colors.LineColor, dtTreeConnectorWidth,
	)
}

func (p TreeViewPainter) PaintEmptyState(canvas widget.Canvas, bounds geometry.Rect) {
	if bounds.IsEmpty() {
		return
	}
	colors := p.resolveColors()
	canvas.DrawText(dtTreeEmptyText, bounds, dtTreeEmptyFontSize, colors.EmptyTextColor, false, widget.TextAlignCenter)
}

func (p TreeViewPainter) PaintExpandIcon(canvas widget.Canvas, s treeview.ExpandIconState) {
	if s.Bounds.IsEmpty() {
		return
	}
	colors := p.effectiveColors(s.ColorScheme)

	cx := s.Bounds.Min.X + s.Bounds.Width()/2
	cy := s.Bounds.Min.Y + s.Bounds.Height()/2

	if s.Expanded {
		// Down-pointing chevron.
		canvas.DrawLine(
			geometry.Pt(cx-dtTreeIconHalfSize, cy-dtTreeIconQuarterSize),
			geometry.Pt(cx, cy+dtTreeIconQuarterSize),
			colors.IconColor, dtTreeIconStrokeWidth,
		)
		canvas.DrawLine(
			geometry.Pt(cx, cy+dtTreeIconQuarterSize),
			geometry.Pt(cx+dtTreeIconHalfSize, cy-dtTreeIconQuarterSize),
			colors.IconColor, dtTreeIconStrokeWidth,
		)
	} else {
		// Right-pointing chevron.
		canvas.DrawLine(
			geometry.Pt(cx-dtTreeIconQuarterSize, cy-dtTreeIconHalfSize),
			geometry.Pt(cx+dtTreeIconQuarterSize, cy),
			colors.IconColor, dtTreeIconStrokeWidth,
		)
		canvas.DrawLine(
			geometry.Pt(cx+dtTreeIconQuarterSize, cy),
			geometry.Pt(cx-dtTreeIconQuarterSize, cy+dtTreeIconHalfSize),
			colors.IconColor, dtTreeIconStrokeWidth,
		)
	}
}

func (p TreeViewPainter) PaintLabel(canvas widget.Canvas, s treeview.LabelState) {
	if s.Bounds.IsEmpty() || s.Text == "" {
		return
	}
	colors := p.effectiveColors(s.ColorScheme)
	color := colors.LabelColor
	if s.Disabled {
		color = color.WithAlpha(dtTreeDisabledAlpha)
	}
	canvas.DrawText(s.Text, s.Bounds, dtTreeLabelFontSize, color, false, widget.TextAlignLeft)
}

func (p TreeViewPainter) PaintRowBackground(canvas widget.Canvas, s treeview.RowPaintState) {
	if s.Bounds.IsEmpty() {
		return
	}
	if s.Hovered && !s.Disabled {
		colors := p.effectiveColors(s.ColorScheme)
		canvas.DrawRect(s.Bounds, colors.HoverColor)
	}
}

func (p TreeViewPainter) PaintSelection(canvas widget.Canvas, s treeview.RowPaintState) {
	if s.Bounds.IsEmpty() || !s.Selected {
		return
	}
	colors := p.effectiveColors(s.ColorScheme)
	canvas.DrawRect(s.Bounds, colors.SelectionColor)

	if s.Focused && !s.Disabled {
		canvas.StrokeRect(s.Bounds, colors.FocusColor, dtTreeFocusBorderWidth)
	}
}

type TreeViewPainter struct {
	Theme *Theme	// nil uses default DevTools dark fallback
}