<image bind:touchstart="onTouchStart" bindtouchmove="q5_onTouchMove" style="left: {{q5_tomato_left}}px; top: {{q5_tomato_top}}px;" src="cloud://cloud1-8gwgkldle8e2a93d.636c-cloud1-8gwgkldle8e2a93d-1324211457/fyss/tomato.png" />

onTouchStart(event) {
        // 获取手指点击屏幕的位置
        const touchX = event.touches[0].clientX;
        const touchY = event.touches[0].clientY;


        // 将位置信息应用到图片的位置属性上
        this.setData({
            'positionLeft': touchX,
            'positionTop': touchY
        });
    },

q5_onTouchMove (e) {
        // 计算手指移动的距离
        const q5_offsetX = e.touches[0].clientX - this.data.positionLeft;
        const q5_offsetY = e.touches[0].clientY - this.data.positionTop;
    
        // 更新按钮的位置，限制每次移动的偏移量
        const newX = this.data.q5_tomato_left + q5_offsetX;
        const newY = this.data.q5_tomato_top + q5_offsetY;
        this.setData({
          q5_tomato_left: newX,
          q5_tomato_top: newY,
          // 更新起始点坐标
          positionLeft: e.touches[0].clientX,
          positionTop: e.touches[0].clientY
        });
    },

为什么起始向上移动全程很丝滑，起始动作向下的话，全程有卡顿感？