在div边框内设置动画图像

Question

我正在尝试动画一个应该在div容器边框内随机移动的图像.我在这里找到了一些设置动画边框的解决方案,但是在图像停留在div中的地方没有.

我有一个例子 - 我需要红色方块在黄色div内移动,即使我向下滚动页面.

我怎样才能做到这一点？

$(document).ready(function() {
    animateDiv();

});

function makeNewPosition($container) {

    // Get viewport dimensions (remove the dimension of the div)
    $container = ($container || $(window))
    var h = $container.height() - 50;
    var w = $container.width() - 50;

    var nh = Math.floor(Math.random() * h);
    var nw = Math.floor(Math.random() * w);

    return [nh, nw];

}

function animateDiv() {
    var $target = $('.a');
    var newq = makeNewPosition($target.parent());
    var oldq = $target.offset();
    var speed = calcSpeed([oldq.top, oldq.left], newq);

    $('.a').animate({
        top: newq[0],
        left: newq[1]
    }, speed, function() {
        animateDiv();
    });

};

function calcSpeed(prev, next) {

    var x = Math.abs(prev[1] - next[1]);
    var y = Math.abs(prev[0] - next[0]);

    var greatest = x > y ? x : y;

    var speedModifier = 0.1;

    var speed = Math.ceil(greatest / speedModifier);

    return speed;

}

div#container {height:100px;width:100px;margin-left: 500px;background-color: yellow;}

div.a {
width: 50px;
height:50px;
 background-color:red;
position:absolute;
    
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div>
<h1>TITLE!</h1>
<p>
Just some test which the red squere won't touch at any point
</p>
</div>
<div id="container">
<div class='a'></div>
</div>

Answer 1

当您给出position:absolute;一个元素时，您必须定义一个元素，position:relative;以便子元素（绝对元素）不会超出其边界。

$(document).ready(function() {
    animateDiv();

});

function makeNewPosition($container) {

    // Get viewport dimensions (remove the dimension of the div)
    $container = ($container || $(window))
    var h = $container.height() - 50;
    var w = $container.width() - 50;

    var nh = Math.floor(Math.random() * h);
    var nw = Math.floor(Math.random() * w);

    return [nh, nw];

}

function animateDiv() {
    var $target = $('.a');
    var newq = makeNewPosition($target.parent());
    var oldq = $target.offset();
    var speed = calcSpeed([oldq.top, oldq.left], newq);

    $('.a').animate({
        top: newq[0],
        left: newq[1]
    }, speed, function() {
        animateDiv();
    });

};

function calcSpeed(prev, next) {

    var x = Math.abs(prev[1] - next[1]);
    var y = Math.abs(prev[0] - next[0]);

    var greatest = x > y ? x : y;

    var speedModifier = 0.1;

    var speed = Math.ceil(greatest / speedModifier);

    return speed;

}

div#container {
  height:100px;
  width:100px;
  margin-left: 500px;
  background-color: yellow; 
  position:relative;/*Added position to the parent container*/
}

div.a {
 width: 50px;
 height:50px;
 background-color:red;
 position:absolute;
    
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div>
<h1>TITLE!</h1>
<p>
Just some test which the red squere won't touch at any point
</p>
</div>
<div id="container">
<div class='a'></div>
</div>

参考链接1：https://css-tricks.com/absolute-relative-fixed-positioining-how-do-they-differ/

现场演示：https://www.w3schools.com/css/tryit.asp ?filename=trycss_position_absolute