javascript - 如何在鼠标位置缩放图像并在 div 上显示结果

Question

我正在尝试缩放图像并将结果显示在光标周围的 div 上，类似于 w3schools确实如此，除了他们在另一张图片上显示结果并且“我不是”。

问题是，缩放相对于鼠标光标并不完全正确，它显示的是最近的像素，但不是正确的像素，我不明白为什么。

这是 snippet .

我的 CSS:

* {
  box-sizing: border-box;
}

.img-zoom-container {
  position: relative;
}

.img-zoom-lens {
  position: absolute;
  border: 1px solid #d4d4d4;
  border-radius: 40px;
  width: 70px;
  height: 70px;
}

.img-zoom-result {
  border: 1px solid #d4d4d4;
  width: 300px;
  height: 300px;
}

.crosshair {
  cursor: crosshair;
}

HTML:

<h1>Image Zoom</h1>

<p>Mouse over the image:</p>

<div class="img-zoom-container crosshair">
  <img id="myimage" src="https://www.pasionfutbol.com/__export/1506450064123/sites/pasionlibertadores/img/2017/09/26/puyol3c.jpg_715985292.jpg">
  <div id="myresult" class="img-zoom-result"></div>
</div>

<p>The image must be placed inside a container with relative positioning.</p>
<p>The result can be put anywhere on the page, but must have the class name "img-zoom-result".</p>
<p>Make sure both the image and the result have IDs. These IDs are used when a javaScript initiates the zoom effect.</p>

JS:

function imageZoom(imgID, resultID) {
  var img, lens, result, cx, cy;
  img = document.getElementById(imgID);
  result = document.getElementById(resultID);
  /*create lens:*/
  lens = document.createElement("DIV");
  lens.setAttribute("class", "img-zoom-lens");
  /*insert lens:*/
  img.parentElement.insertBefore(lens, img);
  /*calculate the ratio between result DIV and lens:*/
  cx = result.offsetWidth / lens.offsetWidth;
  cy = result.offsetHeight / lens.offsetHeight;
  /*set background properties for the result DIV:*/
  lens.style.backgroundImage = "url('" + img.src + "')";
  lens.style.backgroundSize = (img.width * cx) + "px " + (img.height * cy) + "px";
  /*execute a function when someone moves the cursor over the image, or the lens:*/
  lens.addEventListener("mousemove", moveLens);
  img.addEventListener("mousemove", moveLens);
  /*and also for touch screens:*/
  lens.addEventListener("touchmove", moveLens);
  img.addEventListener("touchmove", moveLens);
  function moveLens(e) {
    var pos, x, y;
    /*prevent any other actions that may occur when moving over the image:*/
    e.preventDefault();
    /*get the cursor's x and y positions:*/
    pos = getCursorPos(e);
    /*calculate the position of the lens:*/
    x = pos.x - (lens.offsetWidth / 2);
    y = pos.y - (lens.offsetHeight / 2);
    /*prevent the lens from being positioned outside the image:*/
    if (x > img.width - lens.offsetWidth) {x = img.width - lens.offsetWidth;}
    if (x < 0) {x = 0;}
    if (y > img.height - lens.offsetHeight) {y = img.height - lens.offsetHeight;}
    if (y < 0) {y = 0;}
    /*set the position of the lens:*/
    lens.style.left = x + "px";
    lens.style.top = y + "px";
    /*display what the lens "sees":*/
    lens.style.backgroundPosition = "-" + (x * cx) + "px -" + (y * cy) + "px";
  }
  function getCursorPos(e) {
    var a, x = 0, y = 0;
    e = e || window.event;
    /*get the x and y positions of the image:*/
    a = img.getBoundingClientRect();
    /*calculate the cursor's x and y coordinates, relative to the image:*/
    x = e.pageX - a.left;
    y = e.pageY - a.top;
    /*consider any page scrolling:*/
    x = x - window.pageXOffset;
    y = y - window.pageYOffset;
    return {x : x, y : y};
  }
}

imageZoom("myimage", "myresult");

如您所见，这是来自 w3schools 的复制粘贴代码，但我需要进行上述更改。

Answer 1

您需要调整缩放图像中的位置。

/*display what the lens "sees":*/
var lw=lens.offsetWidth;
var lh=lens.offsetHeight;
// taking here the pos.x of event and scale it with zoom factor , then subtract the lense width divided by zoom factor;
// then some fine tuning : subtracting the 0.5 lense width in the zoomed image 
// UPDATED
var zx=pos.x*cx -(0.5*lw) ; 
var zy=pos.y*cy -(0.5*lh) ; 
lens.style.backgroundPosition = "-" + (zx) + "px -" + (zy) + "px";

希望对您有所帮助:)