asciinema.org/bin/rasterize

#!/usr/bin/env phantomjs

var system = require('system');

if (system.args.length < 6) {
  console.log("usage: " + system.args[0] + " <url> <filename> <format> <selector> <scale>");
  console.log("   ex: " + system.args[0] + " page.html page.png png 'body > div' 2");
  phantom.exit(1);
}

var url = system.args[1];
var filename = system.args[2];
var format = system.args[3];
var selector = system.args[4];
var scale = parseInt(system.args[5], 10);

var page = require('webpage').create();

page.viewportSize = { width: 9999, height: 9999 };
page.zoomFactor = scale;

page.onConsoleMessage = function(msg) {
  console.log('console.log: ' + msg);
};

page.onError = function(msg, trace) {
  console.log('Script error: ' + msg);
  phantom.exit(1);
}

page.onResourceError = function(resourceError) {
  console.log('Unable to load resource (#' + resourceError.id + 'URL:' + resourceError.url + ')');
  console.log('Error code: ' + resourceError.errorCode + '. Description: ' + resourceError.errorString);
  phantom.exit(1);
};

page.open(url, function(status) {
  if (status !== "success") {
    console.log("Failed to load " + url);
    phantom.exit(1);
  }

  var rect = page.evaluate(function(selector) {
    // Alternative to zoomFactor:
    //
    // /* scale the whole body */
    // document.body.style.webkitTransform = "scale(2)";
    // document.body.style.webkitTransformOrigin = "0% 0%";
    // /* fix the body width that overflows out of the viewport */
    // document.body.style.width = "50%";
    //
    // It has small issue with letter spacing though.

    var elements = document.querySelectorAll(selector);

    if (elements.length > 0) {
      return elements[0].getBoundingClientRect();
    }
  }, selector);

  if (!rect) {
    console.log("Couldn't get geometry of requested DOM element");
    phantom.exit(1);
    return;
  }

  page.clipRect = {
    left: rect.left * scale,
    top: rect.top * scale,
    width: rect.width * scale,
    height: rect.height * scale
  };

  page.render(filename, { format: format });
  phantom.exit(0);
});

// vim: ft=javascript