Dynamic Graphics

Generating graphics, charts and graphs for your web site is easy following Mr. Lerner's instructions.
Modifying the Graph

Now that you have seen how to create simple graphs based on various inputs, let us spend a few moments discussing how you can modify the outputs. GIFgraph allows you to change just about every aspect of the graph, including the colors, placement and style of the legend, and the way in which the axes are marked. This is done with the set method. Of course, certain settings are active for only certain types of graphs; for instance, there are no axes on a pie chart, meaning that setting the axis labels will be meaningless.

Here is one example invocation of set:

$graph->set(x_label => "Candidates",
        y_label => "Number of votes",
        title => "Voting results",
     logo => "corplogo.gif",
     zero_axis => 1);

The GIFgraph manual page, available by typing perldoc GIFgraph after installing the package, describes these and many other options in detail. However, the above is probably a good starting point and demonstrates how the various factors describing a chart can be set. In the above example, we label the X axis Candidates, the Y axis Number of votes, include our corporate logo on the chart, and ensure the axes will always begin at the origin (0, 0). There are also options to choose colors and fonts, as well as define how often ticks should appear on each axis—if you read the manual, you will likely be overwhelmed by the wealth of options.

Conclusion

As you can see, it is not particularly difficult to create graphics on the fly from within our CGI program. Even more impressive—as well as generally useful—is the ability to create many types of charts and graphs in only a few lines of code.

Next month, we will take a further look at dynamically generated graphics, looking at a simple application that tracks a user's stock portfolio. That application will revisit two topics we discussed last month, namely HTTP cookies and saving state to a database.

Reuven M. Lerner is an Internet and Web consultant living in Haifa, Israel, who has been using the Web since early 1993. His book Core Perl will be published by Prentice-Hall later this year. Reuven can be reached at reuven@lerner.co.il. The ATF home page, including archives and discussion forums, is at http://www.lerner.co.il/atf/.

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