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Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

            
              <canvas id="canvas" width="1500px" height="1500px"></canvas>
            
          
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              // Canvas DOM 元素 
const canvas = document.getElementById('canvas')
const ctx = canvas.getContext('2d')

//起始點座標
let x1= 0
let y1= 0

// 終點座標
let x2= 0
let y2= 0

// 宣告一個 hasTouchEvent 變數,來檢查是否有 touch 的事件存在
const hasTouchEvent = 'ontouchstart' in window ? true : false

// 透過上方的 hasTouchEvent 來決定要監聽的是 mouse 還是 touch 的事件
const downEvent = hasTouchEvent ? 'ontouchstart' : 'mousedown'
const moveEvent = hasTouchEvent ? 'ontouchmove' : 'mousemove'
const upEvent = hasTouchEvent ? 'touchend' : 'mouseup'

// 宣告 isMouseActive 為滑鼠點擊的狀態,因為我們需要滑鼠在 mousedown 的狀態時,才會監聽 mousemove 的狀態
let isMouseActive = false

canvas.addEventListener(downEvent, function(e){
  isMouseActive = true
})

canvas.addEventListener(downEvent, function(e){
  isMouseActive = true  
  x1 = e.offsetX
  y1 = e.offsetY
  
  ctx.lineWidth = 5
  ctx.lineCap = 'round'
  ctx.lineJoin = 'round'
})

canvas.addEventListener(moveEvent, function(e){
      if(!isMouseActive){
        return
      }
      // 取得終點座標
      x2 = e.offsetX
      y2 = e.offsetY
      
      // 開始繪圖
      ctx.beginPath()
      ctx.moveTo(x1, y1)
      ctx.lineTo(x2, y2)
      ctx.stroke()
      
      // 更新起始點座標
      x1 = x2
      y1 = y2
})

canvas.addEventListener(upEvent, function(e){
  isMouseActive = false
})
            
          
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999px
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