drawSelectionIndicator method
绘制选中状态的视觉反馈
Implementation
void drawSelectionIndicator(Canvas canvas, {double highlightOpacity = 0.3}) {
if (state != DrawingToolState.selected) return;
final bounds = getBounds();
if (bounds.isEmpty) return;
// 绘制高亮背景
final highlightPaint = Paint()
..color = color.withOpacity(highlightOpacity)
..style = PaintingStyle.fill;
canvas.drawRect(bounds.inflate(3.0), highlightPaint);
// 绘制选中边框
final borderPaint = Paint()
..color = Colors.white.withOpacity(0.8)
..strokeWidth = 1.5
..style = PaintingStyle.stroke;
canvas.drawRect(bounds.inflate(5.0), borderPaint);
}