Preface and history of the JpGraph library

PHP has over the last 10 years developed from a rather small language for the enthusiasts to a major platform for WEB based application development. The reason we call it a platform rather than a script language is the fact that when referring to PHP it is impossible not to include the very large library of included standard modules which makes it more of a platform than a scripting language. As such there are more extensions to PHP both in the form of external libraries as well as core language extension than any single person can have a working knowledge of. This means that development teams have to select carefully where best to invest time and training. So how can the JpGraph extension library motivate its existence? Perhaps a quick personal reflection of how this library came about might give some insights.

When I first became aware of PHP at the end of 1998 the PHP 3 version was the new shiny kid on the block after a complete rewrite of the previous PHP2. Initially I proposed to a client I was then working for to use this new script language to build some - what was then - state of the art interfaces to a legacy mainframe system. As part of that some basic graphic capabilities was needed and as part of that work I put together some fairly crude and not very generic small library that would just fit the need to my client. This was not a major part of the development and it didn't make sense at the time to spend a lot of complex design effort into this very small part of the system. After the work for that client was done I felt that I should rewrite the small library I put together so that it would be both a little bit more generic and also a bit more maintainable. (Side note: As part of the contract with the client I was explicitly forbidden to use any object-oriented-technology since my client had been terrible burnt by some previous contractors in this area). Hence the original library was basically a function library and the first thing that was needed was a proper design using a more maintainable OO-design philosophy.

This rewrite of the library and the "plugin" architecture/framework it is based on tried to make the best of the very crude object oriented support available in PHP3 at that time. The support available then was almost nothing more then some syntactic sugar. However, the initial design from then is almost unchanged to this day, almost 11 years later. To the best of my knowledge this makes it one (if not the) oldest object oriented library for PHP that is still actively maintained and developed.

Philosophy of the manual

Writing a good user manual for feature rich library is a bit of a challenge. Learning to efficiently use a library of this size is not a linear undertaking. One start with some basics, jump to a bit that is needed at the moment, (perhaps not fully understanding the details), and then goes back to the beginning again. This makes writing a manual that suits everyone impossible. What we have tried is to mainly follow a "from-the-basics-to-the-advanced" style as much as possible.

At certain times we find ourself in the need of some more advanced concept that have not yet been introduced. In those circumstances we will briefly introduce the concept before making use of it and refer to other parts of the manual that discuss the particular feature in more detail. In this way we hope that the more advanced features will at least register as an area for further exploration even early on in the study of the library and help build up the mental map on what is possible to do in the library. This of course has the result that the same information might be in two or three places, but from a slightly different angle, when it is needed. This manual is deliberately not a long list of API - a detailed description of all API and classes are available in the reference manual.

A final note on the examples shown in this manual might be in place. It is custom to keep introductory examples clean of any real error handling in order to keep them short. We do not believe that this is a good idea. Error and exception handling is one of the most crucial part in design and implementation of any system. For this reason we have included, where appropriate, a basic error handling even though it will make some examples slightly larger.

Typographic conventions used in this manual