Canvas鼠标画线

鼠标按下开始画线,鼠标移动根据鼠标的轨迹去画,鼠标抬起停止画线

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Canvas Drawing</title>
  <style>
    canvas {
      border: 1px solid #000;
    }
  </style>
</head>

<body>
  <canvas id="myCanvas" width="500" height="500"></canvas>

  <script>
    document.addEventListener('DOMContentLoaded', function () {
      const canvas = document.getElementById('myCanvas')
      const ctx = canvas.getContext('2d')
      let isDrawing = false

      function startDrawing (e) {
        isDrawing = true
        draw(e)
      }

      function stopDrawing () {
        isDrawing = false
        ctx.beginPath() // Reset the path for the next draw
      }

      function draw (e) {
        if (!isDrawing) return

        ctx.lineWidth = 5
        ctx.lineCap = 'round'
        ctx.strokeStyle = '#000'

        ctx.lineTo(e.clientX - canvas.offsetLeft, e.clientY - canvas.offsetTop)
        ctx.stroke()
        ctx.beginPath()
        ctx.moveTo(e.clientX - canvas.offsetLeft, e.clientY - canvas.offsetTop)
      }

      canvas.addEventListener('mousedown', startDrawing)
      canvas.addEventListener('mousemove', draw)
      canvas.addEventListener('mouseup', stopDrawing)
      canvas.addEventListener('mouseout', stopDrawing)
    });
  </script>
</body>

</html>

效果图
在这里插入图片描述

和上面效果相同,只是轨迹线换成了直线(鼠标移动始终显示两点直线,只能绘制有一条线)

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Canvas Drawing</title>
  <style>
    canvas {
      border: 1px solid #000;
    }
  </style>
</head>

<body>
  <canvas id="myCanvas" width="500" height="500"></canvas>

  <script>
    document.addEventListener('DOMContentLoaded', function () {
      const canvas = document.getElementById('myCanvas')
      const ctx = canvas.getContext('2d')
      let isDrawing = false
      let startX, startY

      function startDrawing (e) {
        isDrawing = true
        startX = e.clientX - canvas.offsetLeft
        startY = e.clientY - canvas.offsetTop
      }

      function drawLine (e) {
        if (!isDrawing) return

        const endX = e.clientX - canvas.offsetLeft
        const endY = e.clientY - canvas.offsetTop

        ctx.clearRect(0, 0, canvas.width, canvas.height) // Clear the canvas
        ctx.lineWidth = 5
        ctx.lineCap = 'round'
        ctx.strokeStyle = '#000'

        ctx.beginPath()
        ctx.moveTo(startX, startY)
        ctx.lineTo(endX, endY)
        ctx.stroke()
      }

      function stopDrawing () {
        isDrawing = false
      }

      canvas.addEventListener('mousedown', startDrawing)
      canvas.addEventListener('mousemove', drawLine)
      canvas.addEventListener('mouseup', stopDrawing)
      canvas.addEventListener('mouseout', stopDrawing)
    });
  </script>
</body>

</html>

效果图
在这里插入图片描述

效果图和上面相同(可以画多条直线,点击确定按钮会保留最后画的一条线)

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Canvas Drawing</title>
  <style>
    canvas {
      border: 1px solid #000;
      margin-bottom: 20px;
    }

    button {
      display: block;
      margin-top: 10px;
    }
  </style>
</head>

<body>
  <canvas id="myCanvas" width="500" height="500"></canvas>
  <button id="confirmButton">Confirm</button>

  <script>
    document.addEventListener('DOMContentLoaded', function () {
      const canvas = document.getElementById('myCanvas')
      const ctx = canvas.getContext('2d')
      let lines = [] // 画线的数组
      let lines2 = [] // 点击确定后存放的按钮
      let num = 0
      let isDrawing = false
      let startPoint = {}
      let endPoint = {}

      function startDrawing (e) {
        isDrawing = true
        startPoint = {
          x: e.clientX - canvas.offsetLeft,
          y: e.clientY - canvas.offsetTop
        }
      }

      function drawLine (e) {
        if (!isDrawing) return

        endPoint = {
          x: e.clientX - canvas.offsetLeft,
          y: e.clientY - canvas.offsetTop
        }

        ctx.clearRect(0, 0, canvas.width, canvas.height) // Clear the canvas

        ctx.lineWidth = 5
        ctx.lineCap = 'round'
        ctx.strokeStyle = '#000'

        lines.forEach(line => {
          ctx.beginPath()
          ctx.moveTo(line.start.x, line.start.y)
          ctx.lineTo(line.end.x, line.end.y)
          ctx.stroke()
        })

        ctx.beginPath()
        ctx.moveTo(startPoint.x, startPoint.y)
        ctx.lineTo(endPoint.x, endPoint.y)
        ctx.stroke()
      }

      function stopDrawing () {
        if (isDrawing) {
          isDrawing = false
          lines.push({ start: { ...startPoint }, end: { ...endPoint } })
        }
      }

      function confirmLines () {
        lines2.push(lines[lines.length - 1])
        lines = [...lines2]
        ctx.clearRect(0, 0, canvas.width, canvas.height) // Clear the canvas
        if (lines2.length > 0) {
          lines2.forEach((item) => {
            const lastLine = item
            ctx.beginPath()
            ctx.moveTo(lastLine.start.x, lastLine.start.y)
            ctx.lineTo(lastLine.end.x, lastLine.end.y)
            ctx.stroke()
          })
        }
      }

      canvas.addEventListener('mousedown', startDrawing)
      canvas.addEventListener('mousemove', drawLine)
      canvas.addEventListener('mouseup', stopDrawing)
      canvas.addEventListener('mouseout', stopDrawing)

      const confirmButton = document.getElementById('confirmButton')
      confirmButton.addEventListener('click', confirmLines)
    });
  </script>
</body>

</html>