如何实现自动滚动以跟随我的div

Question

I've looked at several tutorials online and a few similar questions on SO but not been able to work out how to make the screen autoscroll left and right so that my #sheep stays in the centre of the screen.

I'm using javascript and jquery to move a simple div across the screen.

Here's my jsfiddle

http://jsfiddle.net/JosephByrne/CkkVr/

What's the best method of making the screen follow my div?

Answer 1

I think you're trying to move the wrong element left/right. I think you need to leave your sheep in the middle of the screen then move the background.

Something like:

var walkLeft = function() {
    $('#background').animate({left:"-=10px",top:"-=2px"}, 100);
    $('#background').animate({left:"-=10px",top:"+=2px"}, 100);
};

var walkRight = function() {
    $('#background').animate({left:"+=10px",top:"-=2px"}, 100);
    $('#background').animate({left:"+=10px",top:"+=2px"}, 100);
};

http://jsfiddle.net/CkkVr/22/ (you'll need to "jump right" to see the sheep), but you get the general idea!

Answer 2

You need something similar to this:

function scrollContainer() {
    var $sheep = $("#sheep");
    $("body").scrollLeft($sheep.position().left + $sheep.width());
}

That utilizes jQuery's scrollLeft() function as well as the position() function (on the sheep).

---

You just need to keep messing with the math until it works out properly...

I've implemented it on the "jump" functions here: http://jsfiddle.net/Dxe8a/11/

function scrollContainer() {
    var $sheep = $("#sheep");
    var $body = $("body");
    var windowWidthOver2 = ($(window).width()/2);
    var pos = $sheep.position().left + windowWidthOver2 - $sheep.width() - 80;
    if($body.width() <= (pos + windowWidthOver2 - $sheep.width() - 80)) {
        $body.width($body.width() + windowWidthOver2);
    }
    $body.scrollLeft(pos);
}

You should alter it so that it looks a bit better, but at least it follows your sheep somewhat.