Changing fonts on the same line

I am trying to determine how to do this and maybe one of you can give 
me some pointers.

What I want to do is create a justified line of text and be able to 
have the font change in that line. For lack of a better example here 
is what I would like to do (html markup shown just for the example):

This is the <B>line</B> that is justified.

And have the word line bold.

The brute force way I can envision doing it would be something like 
this psuedo code:

For purposes of this example I will only concern myself with the Bold 
tag

$linetoprint = "This is the <B>line</B> that is justified."

$f1=$pdf->corefont('Helvetica',-encode=>'latin1');
$f2=$pdf->corefont('Helvetica-Bold',-encode=>'latin1');

while ($linetoprint ne "")
{
	$a = substr($linetoprint,0,1); #get next character
	if ($a eq "<")
	{
		# we found a tag
		if (substr($linetoprint,1,1) eq "/")
		{
			# We found the bold close so restore the 
regular font
			$f1=$pdf->corefont('Helvetica',-
encode=>'latin1');
			# Remove the tag from the line
			$linetoprint = substr($linetoprint,4);
			goto Bypass; #Kludge in this sample
		}
		# we just assume this tag is B for now so change font
		$f2=$pdf->corefont('Helvetica-Bold',-
encode=>'latin1');
		$linetoprint = substr($linetoprint,4);
		goto Bypass; #Kludge in this sample
	}


	# here is where I am not sure how to do in PDF::API2

	$thisletterwidth = What is the width of the character in $a 
using the current font settings?

	if ($thisletterwidth + (What is the current print position on 
this line?) >= (Farthest right I want to print) )
	{
		Insert a little spacing into the current line to 
justify it?
		Start a new line
	}

	Add $a to the current line

	$thislinetoprint = substr($thislinetoprint,1);

Bypass:
}

Bill H