function preprocess () {
	// we'll need the ltm package, so in case it's not loaded...
	echo ('require(ltm)\n');
}

function calculate () {
}

function printout () {
	doPrintout (true);
}

function preview () {
	preprocess ();
	calculate ();
	doPrintout (false);
}

function doPrintout (full) {
	// this function takes care of generating the code for the printout() section. If full is set to true,
	// it generates the full code, including headers. If full is set to false, only the essentials will
	// be generated.

	// let's read all values into php variables for the sake of readable code
	var plot_type        = getValue("plot_type");
	var plot_type_item   = getValue("plot_type_item");
	var inp_items        = getValue("inp_items");
	var spin_from        = getValue("spin_from");
	var spin_to          = getValue("spin_to");
	var annotation       = getValue("annotation");

	// in case there are generic plot options defined:
	var plot_options     = getValue("plotoptions.code.printout");
	var plot_ops_main    = getValue("plotoptions.main");
	var plot_ops_type    = getValue("plotoptions.pointtype");
	var plot_ops_xlab    = getValue("plotoptions.xlab");
	var plot_ops_ylab    = getValue("plotoptions.ylab");

	///////////////////////////////////
	// check for selected options
	var arr_items = "";
	var options = new Array() ;
	if (plot_type == "items" && plot_type_item == "ICC")
		options[options.length] = "type=\"ICC\"" ;
	if (plot_type == "items" && plot_type_item == "IIC")
		options[options.length] = "type=\"IIC\"" ;
	// plot all items?
	if (plot_type == "items" && inp_items) {
		// for user convenience, we replace "-", ";" and space, split all input into an array
		// and join it again, separated by commas:
		arr_items = inp_items.replace(/-/g,":").replace(/\s|;/g,",");
		options[options.length] = "items=c("+arr_items+")";
	}

	// for the test information curve, items must be set to "0":
	if (plot_type == "TIC")
		options[options.length] = "type=\"IIC\", items=0" ;
	// there is no option for standard error curves yet, so we need some extra magic
	// (see the "SEC" section in the plotting function below as well!)
	if (plot_type == "SEC")
		options[options.length] = "type=\"IIC\", items=0, plot=FALSE" ;

	// more advanced options
	// user defined zrange? we'll round it to two digits
	if (spin_from != -3.8 || spin_to != 3.8)
		options[options.length] = "zrange=c("+(Math.round(spin_from*100)/100)+","+(Math.round(spin_to*100)/100)+")" ;
	// annotate lines and show legend?
	if (annotation == "legend")
		options[options.length] = "legend=TRUE" ;
	if (annotation == "plain")
		options[options.length] = "annot=FALSE" ;

	if (full) {
		echo ('rk.header("Birnbaum three parameter model plot")\n');
		echo ('\n');
		echo ('rk.graph.on()\n');
	}
	// only the following section will be generated for full==false
	echo ('try({\n');
	printIndentedUnlessEmpty ('\t', getValue ("plotoptions.code.preprocess"), '', '\n');

	// first we'll check wheter standard error curves should be plotted,
	// because it takes two steps to draw them:
	if (plot_type == "SEC") {
		echo ('	# two steps are needed to plot standard error curves\n');
		echo ('	# first some values are generated...\n');
		echo ('	res <- plot(' + getValue("x"));
		if (options.length > 0) echo(", "+options.join(", "));
		echo (')\n');
		echo ('\n');
		echo ('	# ... and then they\'re used to plot the curves:\n');
		echo ('	plot(res[,"z"], 1/sqrt(res[,"info"]), lwd=2');
		// we give some defaults, but they can be changed via the embedded plot options:
		if (!plot_ops_type) echo(", type=\"l\"");
		if (!plot_ops_xlab) echo(", xlab=\"Ability\"");
		if (!plot_ops_ylab) echo(", ylab=\"Standard Error\"");
		if (!plot_ops_main) echo(", main=\"Stadard Error of Measurement\"");
		if (plot_options) echo(plot_options);
		echo (')\n');
	}
	// and this will be plotted if anything else than stadard error curves are chosen:
	else {
		echo ('	plot(' + getValue("x"));
		if (options.length > 0) echo(", "+options.join(", "));
		if (plot_options) echo(plot_options);
		echo (')\n');
	}

	printIndentedUnlessEmpty ('\t', getValue ("plotoptions.code.calculate"), '\n', '');
	echo ('})\n');

	if (full) echo ('rk.graph.off()\n');
}
