canvas的拖动事件有bug？

<template>  
  <view class="container">  
    <canvas canvas-id="puzzleCanvas" @touchstart="handleStart" @touchmove="handleMove" @touchend="handleEnd"  
            @mousedown="handleStart" @mousemove="handleMove" @mouseup="handleEnd"></canvas>  
  </view>  
</template>  

<script>  
export default {  
  data() {  
    return {  
      ctx: null,  
      pieces: [  
        { x: 0, y: 0, width: 100, height: 100, image: '/static/p1.png' },  
        { x: 100, y: 0, width: 100, height: 100, image: '/static/p2.png' },  
        // 更多拼块  
      ],  
      currentPiece: null,  
      offsetX: 0,  
      offsetY: 0,  
      isDragging: false  
    };  
  },  
  mounted() {  
    const canvas = uni.createCanvasContext('puzzleCanvas', this);  
    this.ctx = canvas;  
    this.drawPieces();  
  },  
  methods: {  
    drawPieces() {  
      this.pieces.forEach(piece => {  
        const img = piece.image;  
        // 根据路径绘制图片  
        this.ctx.drawImage(img, piece.x, piece.y, piece.width, piece.height);  
      });  
      this.ctx.draw();  
    },  
    handleStart(event) {  
        this.$showlog("点击开始")  
      const point = this.getPoint(event);  
      this.currentPiece = this.pieces.find(piece => this.isPointInPiece(point, piece));  
      this.$showlog("currentPiece",this.currentPiece)  
      if (this.currentPiece) {  
        this.offsetX = point.x - this.currentPiece.x;  
        this.offsetY = point.y - this.currentPiece.y;  
        this.isDragging = true;  
      }  
    },  
    handleMove(event) {  
        this.$showlog("点击拖动")  
      if (this.isDragging && this.currentPiece) {  
        const point = this.getPoint(event);  
        this.currentPiece.x = point.x - this.offsetX;  
        this.currentPiece.y = point.y - this.offsetY;  
        this.redrawCanvas();  
      }  
    },  
    handleEnd(event) {  
      this.$showlog("点击结束")  
      this.isDragging = false;  
      this.currentPiece = null;  
    },  
    getPoint(event) {  
        this.$showlog("getPoint",event)  
      const touch = event.touches ? event.touches[0] : event;  
      return { x: touch.clientX, y: touch.clientY };  
    },  
    isPointInPiece(point, piece) {  
      return (  
        point.x > piece.x &&  
        point.x < piece.x + piece.width &&  
        point.y > piece.y &&  
        point.y < piece.y + piece.height  
      );  
    },  
    redrawCanvas() {  
      this.ctx.clearRect(0, 0, 750, 750); // 清空画布，750是canvas的宽度和高度  
      this.drawPieces();  
    }  
  }  
}  
</script>  

<style>  
.container {  
  /* position: relative; */  
  width: 750rpx;  
  height: 450rpx;  
}  

canvas {  
  width: 750rpx;  
  height: 450rpx;  
  background-color: #335566;  
}  
</style>  

代码如上，一个简单的canvas拖动图片的demo，在uniapp内置浏览器中点击图片，出现 了2个奇怪的现象

1、没有拖动，也调用拖动的函数（如图1）
2、明明点击的位置在图片上，而图片的高度是100，得到的clientY=129，明显不对。（如图2）

该代码运行到微信小程序开发者工具，没有上面两个问题。运行改成PC模式也没有上面两个问题