To display any image in a HTML web page, one needs to insert an <IMG> tag
in the HTML web page. When the browser sees the <IMG> tag, it will load the
image using the URL in the <IMG> tag in another HTTP connection.
This is no difference to display a ChartDirector chart in a HTML web page. An
<IMG> tag must be used. In this case, the URL in the <IMG> tag
points to a "ChartDirector script" (a script using ChartDirector to create and
deliver chart images) instead of a static image file.
Thus two scripts can be invoked when displaying a ChartDirector chart in a HTML
web page - the script that create the HTML web page, and the script referenced
in the URL of <IMG> tag that delivers the chart to the browser.
To create a chart in which the data come from a database, there are
several options:
- Perform the database query in the ChartDirector script (the script
referenced in the <IMG> tag) to obtain the data and create the chart.
- Perform the database query in script for the containing HTML page, and pass
the data to the ChartDirector script as HTTP query parameters.
This method allows the data from the database query to be used in multiple
charts in the HTML page, and in the HTML page itself (eg. displayed as tables).
- Same as above, but instead of using HTTP query parameters to pass the
data, use "session variables".
One limitation of HTTP query parameters is the query cannot exceed 2048 bytes,
so it cannot pass too much data. "Session variables" can be used in this case
to transfer data among scripts.
- Perform the database query and create the chart image in the
script for the containing HTML page. Save the chart image to a "session
variable". Use an <IMG> tag inform the browser to pick up the image from
the "session variable".
This approach is commonly used in creating
clickable charts, but it can be used for other charts as well. ChartDirector
has a special method BaseChart.makeSession to support this approach.
Note: When using temporary files, make sure the security settings allow
the web server anonymous user to write to the temporary directory. (By default
anonymous users cannot write to any directory.)
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