Acabo de leer un tutorial bastante bueno sobre como crear un efecto de background en movimiento detrás de un texto con jQuery.
El efecto se hace usando una imagen PNG por delante con el texto transparente
También se usa el buen jQuery y un plugin que hizo Alexander Farkas
/**
* @author Alexander Farkas
* v. 1.21
*/
(function($) {
if(!document.defaultView || !document.defaultView.getComputedStyle){ // IE6-IE8
var oldCurCSS = jQuery.curCSS;
jQuery.curCSS = function(elem, name, force){
if(name === 'background-position'){
name = 'backgroundPosition';
}
if(name !== 'backgroundPosition' || !elem.currentStyle || elem.currentStyle[ name ]){
return oldCurCSS.apply(this, arguments);
}
var style = elem.style;
if ( !force && style && style[ name ] ){
return style[ name ];
}
return oldCurCSS(elem, 'backgroundPositionX', force) +' '+ oldCurCSS(elem, 'backgroundPositionY', force);
};
}
var oldAnim = $.fn.animate;
$.fn.animate = function(prop){
if('background-position' in prop){
prop.backgroundPosition = prop['background-position'];
delete prop['background-position'];
}
if('backgroundPosition' in prop){
prop.backgroundPosition = '('+ prop.backgroundPosition;
}
return oldAnim.apply(this, arguments);
};
function toArray(strg){
strg = strg.replace(/left|top/g,'0px');
strg = strg.replace(/right|bottom/g,'100%');
strg = strg.replace(/([0-9\.]+)(\s|\)|$)/g,"$1px$2");
var res = strg.match(/(-?[0-9\.]+)(px|\%|em|pt)\s(-?[0-9\.]+)(px|\%|em|pt)/);
return [parseFloat(res[1],10),res[2],parseFloat(res[3],10),res[4]];
}
$.fx.step. backgroundPosition = function(fx) {
if (!fx.bgPosReady) {
var start = $.curCSS(fx.elem,'backgroundPosition');
if(!start){//FF2 no inline-style fallback
start = '0px 0px';
}
start = toArray(start);
fx.start = [start[0],start[2]];
var end = toArray(fx.options.curAnim.backgroundPosition);
fx.end = [end[0],end[2]];
fx.unit = [end[1],end[3]];
fx.bgPosReady = true;
}
//return;
var nowPosX = [];
nowPosX[0] = ((fx.end[0] - fx.start[0]) * fx.pos) + fx.start[0] + fx.unit[0];
nowPosX[1] = ((fx.end[1] - fx.start[1]) * fx.pos) + fx.start[1] + fx.unit[1];
fx.elem.style.backgroundPosition = nowPosX[0]+' '+nowPosX[1];
};
})(jQuery);
Y se lo usa dando los parametros con otro script
$(document).ready(function() {
moveBgAround();
});
function moveBgAround() {
//give a random value from 0 to 400 for the X axis and the Y axis
var x = Math.floor(Math.random()*401);
var y = Math.floor(Math.random()*401);
//random generated time it takes to move
var time = Math.floor(Math.random()*1001) + 2000;
//make the background image move!
$('.demo').animate({
backgroundPosition: '(' + (x * -1) + 'px ' + (y * -1) + 'px)'
}, time, "swing", function() {
moveBgAround();
});
}
Y listo tenemos que poner en un DIV un background para que se vaya moviendo con estos script y el PNG por delante para se forme el efecto.
y este seria el resultado: DEMO
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>background en movimiento</title>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"></script>
<script type="text/javascript">
/**
* @author Alexander Farkas
* v. 1.21
*/
(function($) {
if(!document.defaultView || !document.defaultView.getComputedStyle){ // IE6-IE8
var oldCurCSS = jQuery.curCSS;
jQuery.curCSS = function(elem, name, force){
if(name === 'background-position'){
name = 'backgroundPosition';
}
if(name !== 'backgroundPosition' || !elem.currentStyle || elem.currentStyle[ name ]){
return oldCurCSS.apply(this, arguments);
}
var style = elem.style;
if ( !force && style && style[ name ] ){
return style[ name ];
}
return oldCurCSS(elem, 'backgroundPositionX', force) +' '+ oldCurCSS(elem, 'backgroundPositionY', force);
};
}
var oldAnim = $.fn.animate;
$.fn.animate = function(prop){
if('background-position' in prop){
prop.backgroundPosition = prop['background-position'];
delete prop['background-position'];
}
if('backgroundPosition' in prop){
prop.backgroundPosition = '('+ prop.backgroundPosition;
}
return oldAnim.apply(this, arguments);
};
function toArray(strg){
strg = strg.replace(/left|top/g,'0px');
strg = strg.replace(/right|bottom/g,'100%');
strg = strg.replace(/([0-9\.]+)(\s|\)|$)/g,"$1px$2");
var res = strg.match(/(-?[0-9\.]+)(px|\%|em|pt)\s(-?[0-9\.]+)(px|\%|em|pt)/);
return [parseFloat(res[1],10),res[2],parseFloat(res[3],10),res[4]];
}
$.fx.step. backgroundPosition = function(fx) {
if (!fx.bgPosReady) {
var start = $.curCSS(fx.elem,'backgroundPosition');
if(!start){//FF2 no inline-style fallback
start = '0px 0px';
}
start = toArray(start);
fx.start = [start[0],start[2]];
var end = toArray(fx.options.curAnim.backgroundPosition);
fx.end = [end[0],end[2]];
fx.unit = [end[1],end[3]];
fx.bgPosReady = true;
}
//return;
var nowPosX = [];
nowPosX[0] = ((fx.end[0] - fx.start[0]) * fx.pos) + fx.start[0] + fx.unit[0];
nowPosX[1] = ((fx.end[1] - fx.start[1]) * fx.pos) + fx.start[1] + fx.unit[1];
fx.elem.style.backgroundPosition = nowPosX[0]+' '+nowPosX[1];
};
})(jQuery);
</script>
<script type="text/javascript">
$(document).ready(function() {
moveBgAround();
});
function moveBgAround() {
//give a random value from 0 to 400 for the X axis and the Y axis
var x = Math.floor(Math.random()*401);
var y = Math.floor(Math.random()*401);
//random generated time it takes to move
var time = Math.floor(Math.random()*1001) + 2000;
//make the background image move!
$('.demo').animate({
backgroundPosition: '(' + (x * -1) + 'px ' + (y * -1) + 'px)'
}, time, "swing", function() {
moveBgAround();
});
}
</script>
<style>
*{margin:0;paggin:0;border:0}
body{background:#000}
.demo {background-image: url(images/back-inmoving1.jpg);background-color: #fff;width:800px;height:247px; margin:150px auto}
.demo img {display: block;}
</style>
</head>
<body>
<div class='demo'>
<img src="images/back-inmoving.png" alt="" />
</div>
</body>
</html>
Link | Text with Moving Backgrounds With jQuery
Demo | demo
