js 实现以鼠标位置为中心滚轮缩放图片

前言

不知道各位前端小伙伴蓝湖使用的多不多，反正我是经常在用，ui将原型图设计好后上传至蓝湖，前端开发人员就可以开始静态页面的的编写了。对于页面细节看的不是很清楚可以使用滚轮缩放后再拖拽查看，还是很方便的。于是就花了点时间研究了一下。今天分享给大家。

实现

HTML

<div class="container">
    <img id="image" alt="">
</div>
<div class="log"></div>

js

设置图片宽高且居中展示

// 获取dom
const container = document.querySelector('.container');
const image = document.getElementById('image');
const log = document.querySelector('.log');
// 全局变量
let result,
    x,
    y,
    scale = 1,
    minScale = 0.5,
    maxScale = 4,
    isPointerdown = false, // 按下标识
    point = { x: 0, y: 0 }, // 第一个点坐标
    diff = { x: 0, y: 0 }, // 相对于上一次pointermove移动差值
    lastPointermove = { x: 0, y: 0 }; // 用于计算diff
// 图片加载完成后再绑定事件
image.addEventListener('load', function () {
    result = getImgSize(image.naturalWidth, image.naturalHeight, window.innerWidth, window.innerHeight);
    image.style.width = result.width + 'px';
    image.style.height = result.height + 'px';
    x = (window.innerWidth - result.width) * 0.5;
    y = (window.innerHeight - result.height) * 0.5;
    image.style.transform = 'translate3d(' + x + 'px, ' + y + 'px, 0) scale(1)';
    // 拖拽查看
    drag();
    // 滚轮缩放
    wheelZoom();
});
image.src = '../images/liya.jpg';
/**
* 获取图片缩放尺寸
* @param {number} naturalWidth 
* @param {number} naturalHeight 
* @param {number} maxWidth 
* @param {number} maxHeight 
* @returns 
*/
function getImgSize(naturalWidth, naturalHeight, maxWidth, maxHeight) {
    const imgRatio = naturalWidth / naturalHeight;
    const maxRatio = maxWidth / maxHeight;
    let width, height;
    // 如果图片实际宽高比例 >= 显示宽高比例
    if (imgRatio >= maxRatio) {
        if (naturalWidth > maxWidth) {
            width = maxWidth;
            height = maxWidth / naturalWidth * naturalHeight;
        } else {
            width = naturalWidth;
            height = naturalHeight;
        }
    } else {
        if (naturalHeight > maxHeight) {
            width = maxHeight / naturalHeight * naturalWidth;
            height = maxHeight;
        } else {
            width = naturalWidth;
            height = naturalHeight;
        }
    }
    return { width: width, height: height }
}

拖拽查看图片逻辑

// 拖拽查看
function drag() {
    // 绑定 pointerdown
    image.addEventListener('pointerdown', function (e) {
        isPointerdown = true;
        image.setPointerCapture(e.pointerId);
        point = { x: e.clientX, y: e.clientY };
        lastPointermove = { x: e.clientX, y: e.clientY };
    });
    // 绑定 pointermove
    image.addEventListener('pointermove', function (e) {
        if (isPointerdown) {
            const current1 = { x: e.clientX, y: e.clientY };
            diff.x = current1.x - lastPointermove.x;
            diff.y = current1.y - lastPointermove.y;
            lastPointermove = { x: current1.x, y: current1.y };
            x += diff.x;
            y += diff.y;
            image.style.transform = 'translate3d(' + x + 'px, ' + y + 'px, 0) scale(' + scale + ')';
            log.innerHTML = `x = ${x.toFixed(0)}<br>y = ${y.toFixed(0)}<br>scale = ${scale.toFixed(5)}`;
        }
        e.preventDefault();
    });
    // 绑定 pointerup
    image.addEventListener('pointerup', function (e) {
        if (isPointerdown) {
            isPointerdown = false;
        }
    });
    // 绑定 pointercancel
    image.addEventListener('pointercancel', function (e) {
        if (isPointerdown) {
            isPointerdown = false;
        }
    });
}

滚轮缩放逻辑

// 滚轮缩放
function wheelZoom() {
    container.addEventListener('wheel', function (e) {
       let ratio = 1.1;
        // 缩小
        if (e.deltaY > 0) {
            ratio = 1 / 1.1;
        }
        // 限制缩放倍数
        const _scale = scale * ratio;
        if (_scale > maxScale) {
            ratio = maxScale / scale;
            scale = maxScale;
        } else if (_scale < minScale) {
            ratio = minScale / scale;
            scale = minScale;
        } else {
            scale = _scale;
        }
        // 目标元素是img说明鼠标在img上，以鼠标位置为缩放中心，否则默认以图片中心点为缩放中心
        if (e.target.tagName === 'IMG') {
            const origin = { 
                x: (ratio - 1) * result.width * 0.5,
                y: (ratio - 1) * result.height * 0.5
            };
            // 计算偏移量
            x -= (ratio - 1) * (e.clientX - x) - origin.x;
            y -= (ratio - 1) * (e.clientY - y) - origin.y;
        }
        image.style.transform = 'translate3d(' + x + 'px, ' + y + 'px, 0) scale(' + scale + ')';
        log.innerHTML = `x = ${x.toFixed(0)}<br>y = ${y.toFixed(0)}<br>scale = ${scale.toFixed(5)}`;
        e.preventDefault();
    });
}

Demo：jsdemo.codeman.top/html/wheelZ…