draw method

@override void draw(Canvas canvas, Size size, bool deeper)

绘制核心方法

• deeper 当前是否为底层绘制
• 出于性能考虑
• 绘制过程为表层绘制，绘制完成抬起手指时会进行底层绘制

Implementation

@override
void draw(Canvas canvas, Size size, bool deeper) {
  if (startPoint == null || endPoint == null) {
    return;
  }

  canvas.drawLine(startPoint!, endPoint!, paint);
}