Re: [xep-support] Image access when generating PDF

From: David Tolpin <>
Date: Thu Oct 05 2006 - 09:09:19 PDT

> Just curious: Why would XEP care if the graphic has been modified?
> What is the time critical problem that XEP is addressing for it
> to check if a graphic file has been modified in the middle of
> processing?

Hi Earl,

in the currently shipped version of XEP there is a separate subsystem
responsible for retrieval (and caching) of remote resources.

The subsystem optimizes retrieval of images in a way similar to what
browsers do to improve performance. In particular, if a resource retrieved
via HTTP, then a cached copy is used unless the validity time is expired
and the document is modified since the previous retrieval. Local files do
not require this optimization because local access is fast.

This design helped to solve performance problems in the past but is not
the most appropriate one for the purposes of XSL formatting. A better
approach would be to just retrieve remote images once per document, and
leverage optimizations spanning a number of documents to general purpose
resource proxies.

However, the current solution works well enough and provides predictable
and maintainable behaviour. Instead of patching the current legacy code,
RenderX is full speed into development of a new generation of the engine
and tool suite, and the new code shares approximately 0% with the old code

There is a semi-official wiki about the effort:
(accessible as the "developer's zone" from the main site, An online formatter demo (a real formatter with
a few impressive examples) is a demonstration that the thing approaches
the release: .

David Tolpin
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Received on Thu Oct 5 09:16:29 2006

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