Question

我正在制作一个小脚本，使对象（div或img）在给定的帧内可移动和缩放。

然而，我遇到了一些我不太确定的问题，因为我是一个javascript初学者 - 所以解释为什么会出现这些问题将会受到赞赏。

问题：

调用函数start_drag()，while_drag()和stop_drag()会返回undefined - 为什么会这样？应该归还什么？
图像的拖动和移动无法正常工作 - 不是单击鼠标按钮并开始移动图像，我必须单击一次然后开始移动。虽然我将mousedown事件绑定到图像上。我做错了什么？
为什么移动部件不能在移动设备上工作（缩放工作！）？

请看我的小提琴：https://jsfiddle.net/pow4ngbw/15/

Answer 1

现在工作正常，主要是图像css但发现了几个错误（参见新的img属性），还添加了一些调整以使拖动更顺畅。

<!DOCTYPE html>
<html>
<body>
<div id="container">
  <img ondragstart="return false" id="drag-img" src="http://www.patsoy.com/p/2015/09/geometric-patterns-f03phtdx.jpg" />
</div>
<input type="button" id="zoomout" class="button" value="Zoom out">
<input type="button" id="zoomin" class="button" value="Zoom in">
</body>
</html>
<script>

var img_ele = null,
  x_cursor = 0,
  y_cursor = 0,
  x_img_ele = 0,
  y_img_ele = 0;

function zoom(zoomincrement) {
  img_ele = document.getElementById('drag-img');
  var pre_width = img_ele.getBoundingClientRect().width, pre_height = img_ele.getBoundingClientRect().height;
  img_ele.style.width = (pre_width * zoomincrement) + 'px';
  img_ele.style.height = (pre_height * zoomincrement) + 'px';
  img_ele = null;
}

document.getElementById('zoomout').addEventListener('click', function() {
  zoom(0.5);
});
document.getElementById('zoomin').addEventListener('click', function() {
  zoom(1.5);
});

function start_drag() {
  img_ele = this;
  x_img_ele = window.event.clientX - document.getElementById('drag-img').offsetLeft;
  y_img_ele = window.event.clientY - document.getElementById('drag-img').offsetTop;

}

function stop_drag() {
  img_ele = null;
}

function while_drag() {
  var x_cursor = window.event.clientX;
  var y_cursor = window.event.clientY;
  if (img_ele !== null) {
    img_ele.style.left = (x_cursor - x_img_ele) + 'px';
    img_ele.style.top = ( window.event.clientY - y_img_ele) + 'px';

      console.log(img_ele.style.left+' - '+img_ele.style.top);

  }
}

document.getElementById('drag-img').addEventListener('mousedown', start_drag);
document.getElementById('container').addEventListener('mousemove', while_drag);
document.getElementById('container').addEventListener('mouseup', stop_drag);
</script>

<style>
#drag-img {
  cursor: move;
  position: relative;
  width: 500px;
  height: 500px;
}

#container {
  overflow: hidden;
  background: red;
  height: 500px;
  width: 500px;
}

.button {
  width: 200px;
  height: 50px;
}
</style>

Answer 2

我已经获取了Bug的代码，并添加了我需要的功能以及注释中要求的功能。我将其更新为：缩放或平移时，始终将图像保留在容器中，并将实现封装在 zoomer 对象内，以保持全局环境清洁。

<!DOCTYPE html>
<html>
<head>
<style>
#zoom-img {
  cursor: move;
  position: relative;
  width: 500px;
  height: 500px;
}

#zoom-container {
  overflow: hidden;
  background: red;
  height: 500px;
  width: 500px;
}

.button {
  width: 100px;
  height: 50px;
}
</style>
</head>
<body id="fullbody">
<div id="zoom-container">
  <img ondragstart="return false" id="zoom-img" src="https://upload.wikimedia.org/wikipedia/commons/thumb/1/17/Cordillera_de_los_Andes.jpg/1024px-Cordillera_de_los_Andes.jpg" />
</div>
<input type="button" id="zoomout" class="button" value="Zoom out">
<input type="button" id="zoomin" class="button" value="Zoom in">
</body>
</html>
<script>
//
//    This file is derived from the javascript portion of the drag-zoom example
//    at the web site: 
//     https://stackoverflow.com/questions/35252249/move-drag-pan-and-zoom-object-image-or-div-in-pure-js
//

var zoomer = (function () {
    var img_ele = null,
      x_cursor = 0,
      y_cursor = 0,
      x_img_ele = 0,
      y_img_ele = 0,
      orig_width = document.getElementById('zoom-img').getBoundingClientRect().width,
      orig_height = document.getElementById('zoom-img').getBoundingClientRect().height,
      current_top = 0,
      current_left = 0,
      zoom_factor = 1.0;

    return {
        zoom: function (zoomincrement) {
            img_ele = document.getElementById('zoom-img');
            zoom_factor = zoom_factor + zoomincrement;
            if (zoom_factor <= 1.0)
            {
                zoom_factor = 1.0;
                img_ele.style.top =  '0px';    
                img_ele.style.left = '0px';
            }
            var pre_width = img_ele.getBoundingClientRect().width, pre_height = img_ele.getBoundingClientRect().height;
            console.log('prewidth='+img_ele.getBoundingClientRect().width+'; pre_height ='+img_ele.getBoundingClientRect().height);
        //  img_ele.style.width = (pre_width * zoomincrement) + 'px';
        //  img_ele.style.height = (pre_height * zoomincrement) + 'px';
            var new_width = (orig_width * zoom_factor);
            var new_heigth = (orig_height * zoom_factor);

                console.log('postwidth='+img_ele.style.width+'; postheight ='+img_ele.style.height);

            if (current_left < (orig_width - new_width))
            {
                current_left = (orig_width - new_width);
            }
            if (current_top < (orig_height - new_heigth))
            {
                current_top = (orig_height - new_heigth);
            }
            img_ele.style.left = current_left + 'px';
            img_ele.style.top = current_top + 'px';
            img_ele.style.width = new_width + 'px';
            img_ele.style.height = new_heigth + 'px';

            img_ele = null;
        },

        start_drag: function () {
          if (zoom_factor <= 1.0)
          {
             return;
          }
          img_ele = this;
          x_img_ele = window.event.clientX - document.getElementById('zoom-img').offsetLeft;
          y_img_ele = window.event.clientY - document.getElementById('zoom-img').offsetTop;
          console.log('img='+img_ele.toString()+'; x_img_ele='+x_img_ele+'; y_img_ele='+y_img_ele+';')
          console.log('offLeft='+document.getElementById('zoom-img').offsetLeft+'; offTop='+document.getElementById('zoom-img').offsetTop)
        },

        stop_drag: function () {
          if (img_ele !== null) {
            if (zoom_factor <= 1.0)
            {
              img_ele.style.left = '0px';
              img_ele.style.top =  '0px';      
            }
            console.log(img_ele.style.left+' - '+img_ele.style.top);
            }
          img_ele = null;
        },

        while_drag: function () {
            if (img_ele !== null)
            {
                var x_cursor = window.event.clientX;
                var y_cursor = window.event.clientY;
                var new_left = (x_cursor - x_img_ele);
                if (new_left > 0)
                {
                    new_left = 0;
                }
                if (new_left < (orig_width - img_ele.width))
                {
                    new_left = (orig_width - img_ele.width);
                }
                var new_top = ( y_cursor - y_img_ele);
                if (new_top > 0)
                {
                    new_top = 0;
                }
                if (new_top < (orig_height - img_ele.height))
                {
                    new_top = (orig_height - img_ele.height);
                }
                current_left = new_left;
                img_ele.style.left = new_left + 'px';
                current_top = new_top;
                img_ele.style.top = new_top + 'px';

                //console.log(img_ele.style.left+' - '+img_ele.style.top);
            }
        }
    };
} ());

document.getElementById('zoomout').addEventListener('click', function() {
  zoomer.zoom(-0.25);
});
document.getElementById('zoomin').addEventListener('click', function() {
  zoomer.zoom(0.25);
});

document.getElementById('zoom-img').addEventListener('mousedown', zoomer.start_drag);
document.getElementById('zoom-container').addEventListener('mousemove', zoomer.while_drag);
document.getElementById('zoom-container').addEventListener('mouseup', zoomer.stop_drag);
document.getElementById('zoom-container').addEventListener('mouseout', zoomer.stop_drag);

</script>

在纯js中移动（拖动/平移）和缩放对象（图像或div）

2 个答案: