PhantomJS: Webkit-Transform scale causes page to flow outside viewport - css

Question

I'm trying to generate large png screenshots of web pages using PhantomJS, which is built on webkit. I have the application generating screenshots just fine (using their raster.js example.) But, I want the text to be larger (rather than 12-16px) - I don't care about the images becoming grainy. I thought that I could simply scale/zoom the webpage doing something like:
document.documentElement.style.webkitTransform = "scale(2.0)";
But that causes the content of the page to escape the viewport. You can see this if you evaluate that line of code in Chrome. Is it possible to scale a whole web page (duplicating "Ctrl +" functionality of the browser) in JavaScript/Phantom.js?
My current phantom.js script looks like:
var page = new WebPage(),
address, output, size;
if (phantom.args.length < 2 || phantom.args.length > 3) {
console.log('Usage: rasterize.js URL filename');
phantom.exit();
} else {
address = phantom.args[0];
output = phantom.args[1];
page.viewportSize = { width: 1280, height: 1024 };
page.open(address, function (status) {
if (status !== 'success') {
console.log('Unable to load the address!');
} else {
page.evaluate(function () {
document.body.style.webkitTransform = "scale(2.0)";
});
window.setTimeout(function () {
page.render(output);
phantom.exit();
}, 200);
}
});
}

Answer 1

Try
page.zoomFactor=2.0;
The webkitTransform CSS property is not going to do what you want, with or without setting the origin. For one thing, it does not change the dimensions of elements (ie, no relayout occurs, the element(s) are zoomed within their current bounding boxes).

Answer 2

Update
You forgot to set the CSS transform-origin property, so your content expands half up and half down (the default is 50% 50%) and the upper part escapes.
So set it to 0% 0% to get the transform happen only down and right:
document.body.style.webkitTransformOrigin = "0% 0%";
You will also have to set the body width to 50% to avoid it ending twice as large as your viewport:
document.body.style.width = "50%";
Old answer - disregard
This resolves only vertical alignment
Ok, the scaling goes up and down, but the viewport extends only down. The fix fortunately is easy: move your content down of half its height.
Use this as your doubling function and you'll be fine:
page.evaluate(function() {
var h = $('body').height();
$('body').css('position', 'relative');
$('body').css('top', h/2 + 'px');
$('body').css('-webkit-transform', 'scale(2.0)');
});
Be aware anyway that getBoundingClientRect() and page.clipRect behaves weirdly when dealing with this transform.