Programming Web Graphics with Perl & GNU Software
by Shawn P. Wallace


Unconfirmed error reports are from readers.  They have not yet been 
approved or disproved by the author or editor and represent solely the
opinion of the reader.


This page was updated March 9, 2001.


Here's a key to the markup:

        [page-number]: serious technical mistake
        {page-number}: minor technical mistake
        <page-number>: important language/formatting problem
        (page-number): language change or minor formatting problem
        ?page-number?: reader question or request for clarification


UNCONFIRMED errors and comments from readers:


{18} in the header block:
The paragraph reads: 
	
	The header is 13 bytes in length, consisting of the 
	following fields:

The following field descriptions total only 12 bytes.

Does the Global Color Table still start at byte 14? You should also indicate 
if you are zero-based (i.e., byte 14 or 14th byte).


{39} Apparently, there is some problem with the Active State port of Perl and 
named parameters using the CGI.pm module. An example:
 
	print $query -> header(-type => 'image/png',
	-expires => '1d'); # remove from cache tomorrow.

	must instead use an anonymous hash as in
	print $query -> header({'type' => 'image/png',
	'expires' => '1d'}); # remove from cache tomorrow.


{79} paragraph 2:
The author says that GD perl module is now independent of the gd library. Per 
email with the author of the PM module, this is no longer true. You must have 
gd installed in order to compile the GD perl module.

                       
[119] first paragraph:
This is not actually a technical mistake, but is very serious and important to
the chapter. The locaiton of ImageMagick has changed.

You can now download the source from: 
ftp://ftp.simplesystems.org/pub/ImageMagick/.

The new version is incompatible with two verisons of the FreeType library and,
strangely, the older versions of ImageMagick seem to be incompatible with 
newer versions of FreeType as well.

I had problems installing the perl module from CPAN, and I believe the CPAN 
module may not be up-to-date with the module provided in ImageMagick. The Perl
module shoud be installed from the source distribution. In addition, despite 
my intention in configuration, the config script seemed to have not defaulted 
to --with-perl as it says it will, or, if it did, the flag was ignored.

After some fiddling I was able to get everything to install properly (I 
skipped a number of the less useful filetypes' supports, so there may or may 
not have been other issues that I avoided).

After the upgrade, many scripts stopped working properly. A number of methods 
aren't the same.


(162) 2nd header:
The Transform() method is described here, but in more recent verisons of 
ImageMagick and PerlMagick the method has been deprecated in favour of the 
Resize() method.

Transform does not raise an exception but it doesn't do anything either.


(162) 2nd header:
The new parameters for the Annotate() method are as follows:

text=>string, font=>string, pointsize=>integer, density=>geometry, 
stroke=>color name, stroke_width=>integer, fill=>color name, box=>color name, 
geometry=>geometry, gravity=>{NorthWest, North, NorthEast, West, Center, East,
SouthWest, South, SouthEast}, antialias=>{true, false}, x=>integer, 
y=>integer, translate=>float, float, scale=>float, float, rotate=>float, 
skewX=>float, skewY=>float

The font specification seems to require an absolute path, at least for 
TrueType fonts, as opposed to looking for them in the location specified in 
--with-font-path=x as specified during configuration of the makefile. For 
instance, font=>"@/usr/local/fonts/COUR.TTF," not just "@COUR.TTF."

The pen parameter has been apparently deprecated, replaced by stroke and fill.
This also breaks scripts relying on older Annotate() parameters, as it will 
simply draw in black (and when doing so on black, you cannot see the 
"changes").

The new gravity parameter also makes a difference. You specify the start or 
end point of the center of the annotation with this.

I was unable to get Image::Magick to open an HTML file as I was able to do 
before, and I have Ghostscript properly configured. In addition, while opening
a text file was possible, the page was blank.

Note that these changes are not properly documented anywhere. On the new site 
for ImageMagick (http://www.simplesystems.org/ImageMagick/www/perl.html) I was
unable to locate an actual changelog documenting the API modifications -- the 
changes seem to have been made without warning. Further, there is no longer 
good documentation on exactly how specific methods and their properties work 
anymore -- and with a slew of new or changed properties and methods, this is 
frustrating to say the least.

If an updated edition of PWGWPAGS is not in order, at least a full online 
description of the changes at O'Reilly should be available, or else many 
would-be web graphics developers will purchase inaccurate information from ORA.

Please note: it also seems to be impossible to install and properly configure 
an older version of Image::Magick with a newer FreeType library and get the 
new FreeType recognized.


{291} The counter.pl script doesn't work. I get a Segmentation Fault whenever 
I try running it. I've ran it using a RH5.2 Linux with perl 5.004_05 and on a 
System V 4.0 with perl 5.005_3. I even copied it and BrokenImage.pm directly 
from your web site here and ran it, and it still won't go. The image files 
(0.gif..9.gif) are in a directory named "default." The countfile is 
countfile.txt layed out as described in the book (current count followed on 
the next line with allowed hosts). 


{291} counter.pl:
I was also unable to get the counter.pl script to function. I created the 
BrokenImage.pm file which seems to work correctly. I get errors reading:

Can't call method "getBounds" without a package or object reference at 
/web/cgi-bin/counter/counter.pl line 88.

This is on the HP-UX platform running Apache.


{291} counter.pl:
The counter.pl program as written in the book does not function correctly. A 
way to make this function is to comment out the "use strict;" line and change 
the "$d = newFromGif GD::Image(*DIGIT);" to "$d = newFromGif 
GD::Image(DIGIT);" (remove the *).

Upon doing this the script will function correctly without the strict module. 
Removing the * and leaving the strict module throws an error stating that 
DIGIT is not alowed when using the strict module.


{291} another correction to counter.pl:
To get the counter.pl script running while using the strict module, you simply
need to change the following line:

	$d = newFromGif GD::Image(*DIGIT);

Change the end of the line to match the following:

	$d = newFromGif GD::Image("DIGIT");

You will also want to do some checking for defined variables throughout the 
program to get rid of a few other warnings. For example, I changed the 
following lines:

	my $count = 0;
	flock COUNT, LOCK_EX;
	$count = <COUNT>;
	my $users = <COUNT>;
	chop($users);

to:

	flock COUNT, LOCK_EX;
	my $count = <COUNT>;
	$count = 0 unless(defined($count));
	my $users = <COUNT>;
	$users = '' unless(defined($users));
	chop($users);

Other minor changes like this can make the code error free and fully 
functional. These changes here should do the trick. Check your error log files
if there is something amiss.