Random Movement in a Fixed Container

问题:

I'm looking to create something that can move randomly inside of a fixed div container. I love the way the object moves in this example that I found searching this website...

http://jsfiddle.net/Xw29r/15/

The code on the jsfiddle contains the following:

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

});

function makeNewPosition(){

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

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

return [nh,nw];    

}

function animateDiv(){
var newq = makeNewPosition();
var oldq = $('.a').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;

}​

CSS:

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

However, I don't believe the code above constricts that object at all. I need my object to move randomly inside of a container that is let's say for now... 1200px in width and 500px in height.

Can someone steer me in the right direction? I'm super new to coding so I'm having a hard time finding an answer on my own.

回答1:

Here is a jsfiddle with the functionality you're seeking: http://jsfiddle.net/2TUFF/

JavaScript:

$(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;

}​

HTML:

<div id="container">
<div class='a'></div>
</div>​

CSS:

div#container {height:100px;width:100px;}

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

}​

This will allow you to create a wrapping element with any height/width and have the floating element keep within its container's area.

回答2:

Add a wrapper element around it and update the jQuery to limit the dimensions.

<div id="wrap">
    <div class='a'></div>
</div>

​

// Get viewport dimensions (remove the dimension of the div)
    var h = $('#wrap').height() - 50;
    var w = $('#wrap').width() - 50;

Here's an updated fiddle: http://jsfiddle.net/Xw29r/375/