How to create dynamic diagonal line from left-bottom to right-top corner?

Daniel Ramirez-Escudero picture Daniel Ramirez-Escudero · Jan 7, 2013 · Viewed 10.1k times · Source

I've created a simple layout where I have three divs which interact. One is the logo in the middle of the screen and the other are two blocks which with jQuery are moved out of the screen. I used the skew option from CSS to apply a degree transformation. I would like to apply the certain degree depending on the screen, so this degree will apply to all screens correctly.

Visual example: http://jsfiddle.net/6a93T/1/

For now I have this code:

HTML:

<html>
    <header>
        <link rel="stylesheet" type="text/css" href="css/reset.css">
        <link rel="stylesheet" type="text/css" href="css/style.css">
        <script type="text/javascript" src="http://code.jquery.com/jquery-latest.js"></script>
        <script type="text/javascript" src="js/jq.animation.js"></script>
    </header>
    <body>
        <div id="preloader">
            <div id="blocktop"></div>
            <div id="logo"></div>
            <div id="loadline"></div>
            <div id="blockbottom"></div>
        </div>
    </body>
</html>

CSS:

html{
    overflow: hidden;
}


#preloader{
    width: 100%;
    height: 100%;
}

#logo{
    background-image: url('../img/logotest.png');
    width: 300px;
    height: 300px;
    display: block;
    position: fixed;
    top: 50%;
    left: 50%;
    margin-left: -150px;
    margin-top: -150px;
    z-index: 1000;
}


#blocktop{
    background-color: #fff4ed;
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0px;
    left: -50%;
    z-index: 10;

    transform: skew(-45deg);
     -o-transform: skew(-45deg);
     -moz-transform: skew(-45deg);
     -webkit-transform: skew(-45deg);
}

#blockbottom{
    background-color: #ff7f33;
    width: 100%;
    height: 100%;
    position: absolute;
    bottom: 0px;
    right: -50%;

    transform: skew(-45deg);
     -o-transform: skew(-45deg);
     -moz-transform: skew(-45deg);
     -webkit-transform: skew(-45deg);

}

jQuery:

$(document).ready(function(){

    /*$("button").click(function() */
        setTimeout(function(){

        $("#blocktop").animate({
        left: '-120%',
        opacity: '0'},
        800
      );

        $("#blockbottom").animate({
        right: '-120%',
        opacity: '0'},
        800
      );


        $('#logo').fadeOut('700')
    },2000);

}); 

Answer

Blazemonger picture Blazemonger · Jan 7, 2013

Use trigonometry to compute the desired angle:

var angle = Math.atan2($(window).width(),$(window).height()); // in radians
$('#blocktop,#blockbottom').css('transform','skew(-'+angle+'rad)');

(Note for math geeks and other pedants: the arctangent would normally take the height divided by the width, not the other way around. In this case, however, we're skewing a vertical line instead of a horizontal one, so the above code gives the desired result.)

Note that newer versions of jQuery will automatically add the necessary -webkit- or -moz- prefix to that CSS transform property.

You might also want to display:none the elements until the above code can alter the angle, and then show() them immediately after the angle is computed:

$('#blocktop,#blockbottom').css('transform', 'skew(-' + angle + 'rad)')
    .add('#logo').show();

http://jsfiddle.net/mblase75/6a93T/10/