To use caching in your script you must supply a suitable file name which will be used to store the image in the cache. You can also supply a timeout value indicating how many minutes the cached image should be considered valid.
These parameters are supplied in the initial Graph() method call which should be among the first in your script. Instead of manually specifying a file name to be used you could often use the special name "auto". If the filename is specified as "auto" the cashed image will then be named the same as the image script but with the correct extension depending on what image format have been chosen.
If you don't specify a file name no caching will be used no matter the settings of USE_CACHE (without a file name it is impossible!)
The following call to Graph() shows a typical use of the cache.
$graph = new Graph(300,200 ,"auto",60)
The above code will use the automatic filename and a make the cache valid for 60 minutes.
So, how does this all work now?
The first time you call your script (no cached image) everything will be as usual, the script will run and you will in the end send back the image to the browser. However if you have the caching enabled JpGraph will automatically have stored a copy of the generated image in the cache directory.
The next time you call the script the first thing that happens in the initial Graph() is that it will go and check in the cache directory if the named image exists there. If this is the case it will also checks that the image isn't too old (as compared to the specified timeout value). If the image is valid then the image will be streamed straight back from the image file to the browser and the script will end it's execution.
Hence, if the image is found in the cache no code lines after the initial Graph() call will be executed
The design decision behind this is that your image script code never has to include anything special to make full use of the cache. It will just automatically work.