这看起来应该很简单，但出于某种原因我无法完全理解它。我在“视口(viewport)”div 中有一个图像，其溢出属性设置为隐藏。

我已经使用 jQuery UI 实现了一个简单的缩放和平移，但是我无法让缩放看起来像是从视口(viewport)的中心开始。我从 Photoshop 中做了一些截屏视频，我试图重现这种效果:http://dl.dropbox.com/u/107346/share/reference-point-zoom.mov

在 PS 中，您可以调整缩放引用点，对象将从该点开始缩放。显然，这对于 HTML/CSS/JS 是不可能的，所以我试图找到合适的 left 和 top CSS 值来模拟效果。

这是有问题的代码，删除了一些不必要的位:

html

<div id="viewport">
    <img id="map" src="http://dl.dropbox.com/u/107346/share/fake-map.png" alt="" />
</div>

<div id="zoom-control"></div>

javascript

$('#zoom-control').slider({
    min: 300,
    max: 1020,
    value: 300,
    step: 24,
    slide: function(event, ui) {
        var old_width = $('#map').width();
        var new_width = ui.value;
        var width_change = new_width - old_width;
        $('#map').css({
            width: new_width,

            // this is where I'm stuck...
            // dividing by 2 makes the map zoom
            // from the center, but if I've panned
            // the map to a different location I'd
            // like that reference point to change.
            // So instead of zooming relative to
            // the map image center point, it would
            // appear to zoom relative to the center
            // of the viewport. 
            left: "-=" + (width_change / 2),
            top: "-=" + (width_change / 2)
        });
    }
});

这是 JSFiddle 上的项目:http://jsfiddle.net/christiannaths/W4seR/

最佳答案

这是可行的解决方案。我将在下次编辑时解释逻辑。

函数逻辑:

• 总结:记住图片的中心位置，相对。
  宽度和高度的计算类似，我只解释高度的计算
  详细的解释只是函数逻辑的一个例子。可以在答案底部找到具有不同变量名称的真实代码。

  1. 计算#map 相对于#viewport 的中心(x,y)。这可以通过使用 offset() 来完成。 , height()和 width()方法。
     

     // Absolute difference between the top border of #map and #viewport
     var differenceY = viewport.offset().top - map.offset().top;
     // We want to get the center position, so add it.
     var centerPosition = differenceY + viewport.height() * 0.5;
     // Don't forget about the border (3px per CSS)
     centerPosition += 3;
     // Calculate the relative center position of #map
     var relativeCenterY = centerPosition / map.height();
     // RESULT: A relative offset. When initialized, the center of #map is at
     //  the center of #viewport, so 50% (= 0.5)
     // Same method for relativeCenterX
     

  2. 计算新的顶部和左侧偏移量:

     // Calculate the effect of zooming (example: zoom 1->2 = 2)
     var relativeChange = new_width / old_width;
     // Calculate the new height
     var new_height = relativeChange * old_height;
     // Calculate the `top` and `left` CSS properties.
     // These must be negative if the upperleft corner is outside he viewport
     // Add 50% of the #viewport's height to correctly position #map
     //   (otherwise, the center will be at the upperleft corner)
     var newTopCss = -relativeCenterY * new_height + 0.5 * viewport.height();
     

  3. 更改 CSS 属性

     map.css("top", newTopCss);
     

演示:http://jsfiddle.net/W4seR/12/

var map = $('#map');
var viewport = $('#viewport');
// Cache the size of the viewport (300x300)
var viewport_size = {
    x: viewport.width(),
    y: viewport.height()
};

map.draggable();

$('#zoom-control').slider({
    min: 300,
    max: 1020,
    value: 300,
    step: 24,
    create: function() {
        map.css({
            'width': 300,
            'left': 0,
            'top': 0
        });
    },
    slide: function(event, ui) {
        var old_width = map.width();
        var old_height = map.height();
        var viewport_offset = viewport.offset();
        var offset = map.offset();
        offset = {
            top: viewport_offset.top - offset.top + .5*viewport_size.y +3,
            left: viewport_offset.left - offset.left + .5*viewport_size.x +3
        };
        // Relative offsets, relative to the center!
        offset.top = offset.top / old_height;
        offset.left = offset.left / old_width;

        var new_width = ui.value;
        var relative = new_width / old_width;
        var new_height = relative * old_height;

        offset = {
            top: -offset.top * new_height + .5*viewport_size.y,
            left: -offset.left * new_width + .5*viewport_size.x
        };

        var css_properties = {
            width: new_width,
            left: offset.left,
            top: offset.top
        };

        map.css(css_properties);

        trace((map.position().left));
    }
});

关于Javascript (jQuery) 将图像缩放到其容器的中心点，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/8678374/