Update: As of version 3.1, desktop scaling is now built into in5 and can be found in the Advanced section of the export dialog.
It can also be easily applied to mobile devices.
This can be done with some custom code by adding the following code as a .js file using the Resources section of the in5 dialog:
$(function(){
function scaleForDesktop() {
var targ = (true || $('.activePage').is(':empty')) ? $('.page') : $('.activePage');
var targW = targ.width(), winW = $(window).innerWidth(),
xScaleFactor = winW/targW, yScaleFactor = $(window).innerHeight()/targ.height(),
scaleFactor = (xScaleFactor < yScaleFactor) ? xScaleFactor : yScaleFactor;
var prefixes = ['','-ms-','-webkit-','-moz-'];
var n = prefixes.length;
var xorigin = (winW > targW) ? '50% 0 0' : '0% 0 0'
while(n--){
$('#container').css(prefixes[n]+'transform', 'scale('+scaleFactor+','+scaleFactor+')').css(prefixes[n]+'transform-origin', xorigin);
}
}
if(!touchEnabled){
scaleForDesktop();
$(window).on('load resize', function() { scaleForDesktop(); });
}
});
Some additional CSS may be required depending on the document and Page Format.
For multi-page formats (Baker Framework & Liquid State Publishing System),
change $('#container') to $('#page')
This may only be necessary if you're using the built-in back & next navigation.
For the Vertical Slider, you may want to add the following:
$('#container .anythingSlider-in5').css('padding',0);
before the while line.