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需求：长按鼠标左键框选区域，松开后放大该区域，继续框选继续放大，反向框选恢复原始状态

实现思路：根据鼠标的落点，放大要显示的内容（内层盒子），然后利用水平偏移和垂直偏移，让外层展示的窗口（外层盒子）只看到刚刚框选的大概区域，具体代码如下

<template><div><divclass="selectable_container"@mousedown="handleMouseDown"@mousemove="handleMouseMove"@mouseup="handleMouseUp"><divclass="zoomable_element":style="{userSelect: 'none',left: innerLeft + 'px',top: innerTop + 'px',width: innerWidth + 'px',height: innerHeight + 'px',}"><imgsrc="./img/test1.jpg"style="width: 100%;height: 100%;user-select: none;pointer-events: none;"alt=""/></div><div class="selectable_element" id="selectable_element"></div></div></div>
</template><script>
export default {data() {return {startX: 0,startY: 0,endX: 0,endY: 0,isSelecting: false, //是否正在款选closeFlag: false, //是否退出放大状态offsetinner_left: 0, //外层容器水平偏移offsetinner_top: 0, //外层容器垂直偏移outerWidth: 0, //外层盒子宽度outerHeight: 0, //外层盒子高度zoomRatio: 1,innerWidth: "100%", //内层盒子宽度 初始状态等于外层盒子innerHeight: "100%", //内层盒子高度innerTop: 0, //内层盒子垂直偏移innerLeft: 0, //内层盒子水平偏移selectionLeft: 0, //框选区域水平偏移selectionTop: 0, //框选区域垂直偏移selectionWidth: 0, //框选区域宽度selectionHeight: 0, //框选区域高度,};},mounted() {const dom_mask = window.document.querySelector(".selectable_container");const rect_select = dom_mask.getClientRects()[0];this.offsetinner_left = rect_select.left; //水平偏移this.offsetinner_top = rect_select.top; //垂直偏移this.outerWidth = Math.ceil(rect_select.width);this.outerHeight = Math.ceil(rect_select.height);this.innerWidth = this.outerWidth;this.innerHeight = this.outerHeight;},methods: {handleMouseDown(event) {if (event.button === 0) {// 判断是否为鼠标左键按下this.startX = event.clientX - this.offsetinner_left;this.startY = event.clientY - this.offsetinner_top;this.isSelecting = true;var dom = document.getElementById("selectable_element");if (dom) {dom.style.left = this.startX + "px";dom.style.top = this.startY + "px";}}},handleMouseMove(event) {if (this.isSelecting) {this.closeFlag = false;this.endX = event.clientX - this.offsetinner_left;this.endY = event.clientY - this.offsetinner_top;var selectionLeft, selectionTop, selectionWidth, selectionHeight;selectionWidth = Math.abs(this.endX - this.startX);selectionHeight = Math.abs(this.endY - this.startY);// 右下if (this.endY >= this.startY && this.endX >= this.startX) {selectionLeft = this.startX;selectionTop = this.startY;}// 左下else if (this.endY >= this.startY && this.endX <= this.startX) {selectionLeft = this.endX;selectionTop = this.startY;}// 右上else if (this.endY <= this.startY && this.endX >= this.startX) {selectionLeft = this.startX;selectionTop = this.endY;}// 左上else if (this.endY <= this.startY && this.endX <= this.startX) {selectionLeft = this.endX;selectionTop = this.endY;this.closeFlag = true;}selectionLeft = Math.ceil(selectionLeft);selectionTop = Math.ceil(selectionTop);selectionWidth = Math.ceil(selectionWidth);selectionHeight = Math.ceil(selectionHeight);var dom = document.getElementById("selectable_element");if (dom) {dom.style.left = selectionLeft + "px";dom.style.top = selectionTop + "px";dom.style.width = selectionWidth + "px";dom.style.height = selectionHeight + "px";}this.selectionLeft = 0 - this.innerLeft + selectionLeft;this.selectionTop = 0 - this.innerTop + selectionTop;this.selectionWidth = selectionWidth;this.selectionHeight = selectionHeight;}},handleMouseUp(event) {// 判断是否为鼠标左键松开if (event.button === 0 && this.isSelecting) {// 左上清除if (this.closeFlag) {this.isSelecting = false;this.closeFlag = false;var dom = document.getElementById("selectable_element");if (dom) {dom.style.left = "0px";dom.style.top = "0px";dom.style.width = "0px";dom.style.height = "0px";}this.innerWidth = this.outerWidth;this.innerHeight = this.outerHeight;this.innerLeft = 0;this.innerTop = 0;return;}this.isSelecting = false;this.zoomRatio = Math.min(this.outerWidth / this.selectionWidth,this.outerHeight / this.selectionHeight).toFixed(2);this.zoomRatio = Number(this.zoomRatio);// console.log(this.zoomRatio);var innerWidth = Math.ceil(this.innerWidth * this.zoomRatio);var innerHeight = Math.ceil(this.innerHeight * this.zoomRatio);var innerLeft = 0 - this.selectionLeft * this.zoomRatio;var innerTop = 0 - this.selectionTop * this.zoomRatio;// 居中处理innerLeft =innerLeft +(this.outerWidth - this.selectionWidth * this.zoomRatio) / 2;innerTop =innerTop +(this.outerHeight - this.selectionHeight * this.zoomRatio) / 2;// 补位处理if (innerWidth + innerLeft < this.outerWidth) {// console.log("水平补位");innerLeft = innerLeft + this.outerWidth - (innerWidth + innerLeft);}if (innerHeight + innerTop < this.outerHeight) {// console.log("垂直补位");innerTop = innerTop + this.innerHeight - (innerHeight + innerTop);}this.innerWidth = innerWidth;this.innerHeight = innerHeight;this.innerLeft = innerLeft;this.innerTop = innerTop;var dom = document.getElementById("selectable_element");if (dom) {dom.style.left = "0px";dom.style.top = "0px";dom.style.width = "0px";dom.style.height = "0px";}}},},
};
</script>
<style lang="scss" scoped>
// 外层可视窗口
.selectable_container {position: relative;width: 800px;height: 450px;border: 1px solid #ccc;overflow: hidden;
}
// 框选动作临时盒子
.selectable_element {position: absolute;border: 1px solid red;
}
// 内层内容盒子 需要缩放
.zoomable_element {position: absolute;left: 0;top: 0;
}
</style>