javascript - 如何根据滚动位置缩小图像宽度

Question

我希望根据滚动缩小 Logo

到目前为止，我有这样的东西

logoSize = function(){
    var headerOffset = $(window).height() - 650;
    var maxScrollDistance = 1300;
    $(window).scroll(function() {
        var percentage = maxScrollDistance / $(document).scrollTop();
        if (percentage <= headerOffset) {
            $('.logo').css('width', percentage * 64);
        }
        console.log(percentage);
    });
}

logoSize();

我已经很接近了，但是图像要么开始太宽，要么缩小得太快，我需要它发生在滚动的前 650 像素，如你所见 - 有什么想法吗？也许百分比宽度会更好？

Answer 1

我已经根据您心中有目标大小的假设重写了您的代码，例如滚动 650 像素后，您希望图像宽度为 250 像素。

它在原始大小和目标大小之间平滑滚动，并考虑到窗口高度可能小于最大滚动距离的事实:

logoSize = function () {
    // Get the real width of the logo image
    var theLogo = $("#thelogo");
    var newImage = new Image();
    newImage.src = theLogo.attr("src");
    var imgWidth = newImage.width;

    // distance over which zoom effect takes place
    var maxScrollDistance = 650;

    // set to window height if that is smaller
    maxScrollDistance = Math.min(maxScrollDistance, $(window).height());

    // width at maximum zoom out (i.e. when window has scrolled maxScrollDistance)
    var widthAtMax = 500;

    // calculate diff and how many pixels to zoom per pixel scrolled
    var widthDiff = imgWidth - widthAtMax;
    var pixelsPerScroll =(widthDiff / maxScrollDistance);

    $(window).scroll(function () {
        // the currently scrolled-to position - max-out at maxScrollDistance
        var scrollTopPos = Math.min($(document).scrollTop(), maxScrollDistance);

        // how many pixels to adjust by
        var scrollChangePx =  Math.floor(scrollTopPos * pixelsPerScroll);

        // calculate the new width
        var zoomedWidth = imgWidth - scrollChangePx;

        // set the width
        $('.logo').css('width', zoomedWidth);
    });
}

logoSize();

参见http://jsfiddle.net/raad/woun56vk/一个工作示例。