var myWidth = 0, myHeight = 0;
var imagenes = new Array("dunas.jpg","arbol.jpg","paisaje4.jpg","hojas.jpg","hierba.jpg","paisaje.jpg","tulipanes.jpg","girasoles.jpg","lapices.jpg","montana.jpg","paisaje2.jpg","paisaje3.jpg","paja.jpg");



function tamLetra(valor){
    var letra = document.getElementById("principal").style.fontSize;
    
    letra = letra.substring(0,letra.length-2);
   
    if(valor == 1){        
        letra = parseInt(letra) + 1;       
    }
    if(valor == -1){        
        letra = parseInt(letra) - 1;       
    }
    if(valor == 0){
        letra="12";
    }
   
    document.getElementById("principal").style.fontSize=letra+"px";
    
}

function calcularTamanyo(){
    if( typeof( window.innerWidth ) == 'number' ) {
        //Non-IE
        myWidth = window.innerWidth;
        myHeight = window.innerHeight;
    } else if( document.documentElement && ( document.documentElement.clientWidth || document.documentElement.clientHeight ) ) {
        //IE 6+ in 'standards compliant mode'
        myWidth = document.documentElement.clientWidth;
        myHeight = document.documentElement.clientHeight;
    } else if( document.body && ( document.body.clientWidth || document.body.clientHeight ) ) {
        //IE 4 compatible
        myWidth = document.body.clientWidth;
        myHeight = document.body.clientHeight;
    }
    document.getElementById("imagen").style.height=myHeight-60+"px"
    document.getElementById("texto").style.marginTop=(myHeight-190)*0.1+"px"
    //   document.getElementById("texto").style.marginTop=100+"px"
    cambiarImagen();
    
    
}

function cambiarImagen(){
    var n = Math.random()*(imagenes.length-1);
    n = Math.round(n);
    //n = n % imagenes.length;
    document.getElementById("fondoCabecera").style.backgroundImage = "url(/imagenes/"+imagenes[n]+")";
    document.getElementById("fondoCabecera").style.backgroundRepeat ="no-repeat";    
}