14 Feb
2012
14 Feb
'12
7:59 a.m.
Would be interesting to be moved as documentation on xwiki.org… :)
Best place IMO would be to create an extension for the Image Plugin on
extensions.xwiki.org and document it.
Thanks
-Vincent
On Feb 14, 2012, at 7:56 AM, Sergiu Dumitriu wrote:
On 02/12/2012 05:54 PM, Paul Libbrecht wrote:
Hello fellow xwiki users,
we discovered recently the usage of the width parameter when delivering a picture from an
xwiki document attachment.
Surprisingly this is available in our production server, based on the grumpy xwiki 1.5,
but has not been used in the UI of Curriki which has, however, been made by a team of
XWiki SàRL originally.
Yes, this has been implemented for a very long time. If I remember correctly, it might
have been introduced even before 1.0, or at least very soon after that.
- can someone describe me how this feature is
working?
Basically, whenever an image download request is processed, the ImagePlugin intercepts it
via the downloadAttachment plugin SPI method, and, if there are width or height request
parameter, instead of serving the original attachment, it will create a new fake
attachment holding the resized image.
- is the resulting downscaled image cached in
file or in ram?
There's a filesystem cache for resized images, indeed, so that the same file
isn't scaled for each request. Still, when downloading a specific image, it will be
held in memory as any XWikiAttachment object.
- has there been a different implementation
between the current xwiki (e.g. 3.4) and 1.5?
Yes, kind of. It used to be all in
https://github.com/xwiki/xwiki-platform/blob/c9b8a703cff266363782eee623ff4e…
but the image scaling code has been moved out of the plugin, and is now in
https://github.com/xwiki/xwiki-platform/blob/master/xwiki-platform-core/xwi…
(the call to this component is still in the plugin, though).
There have been a few changes and improvements between the two versions. Besides the
width and height parameters, now there's support for a "quality" parameter,
a number between 0 and 1 controlling the compression quality for JPEG files, and a
"keepAspectRatio" parameter which means that in case both a width and a height
are specified, the image will be scaled with the same aspect ratio to fit within the
specified width and height.
- except for the CPU hogging of computing the
downscaled version, is there any reason not to use this feature? (e.g. RAM overloading?).
It should be used as much as possible. The only problems are the extra storage needed for
storing thumbnails, and the extra CPU time needed to scale, or at least to access the
cached file from the disk.
In recent versions this feature has been used more and more, so most places where images
are used at a different size should already be making use of this feature.
thanks in advance
Paul
--
Sergiu Dumitriu
http://purl.org/net/sergiu/
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