Filter Services

[Fred Kiefer]

During FOSDEM Richard and I discussed the usage of filter services for 
image conversion in gui. This is an old topic and I was always to lazy 
to implement it. With Eric's image converter with Ghostscript and 
Imagemagik there was finally more than enough reason to do it. It turned 
out that the code in NSImageRep to support this was easy to write. 
Richard just had to rewrite DO for the filter service, which had been 
corrupted a few years back, and things were working. Or rather more or 
less so.
I used Ink as my test platform and inserted a PS file into a document, 
getting its image converted to tiff on the way. It turns out that 
NSLayoutManager cannot handle attachments as the last character. I 
couldn't find the reason for that up to now. My example service was just 
a shell script using Ghostscript, here the problem was that Ghostscript 
when used with an output pipe cannot produce correct tiff images 
readable with GNUstep. Richard came up with the idea to write into a 
temporary file and pipe this back via cat. Next there was a problem 
converting the black image that GS produced into RGB, which I managed to 
track down today. Still there are tiff images that get displayed 
correctly as attachments in Ink and others that wont.

So apart from these little issues filter services are working now for 
images!

How to test it:
All you need is a filter program and a service .plist. Attached you will 
find the ones I am using to test things. You will need to adjust the 
path to the gs.sh shell script.
That we use NSTypedFileContentsPboardType:tiff instead of 
NSTIFFPboardType is due to a limitation in the code that converts 
between file types and pasteboard types. We should fix that or rather 
move on to UTI.

The next step would be to write similar support for pasteboard type 
filtering and then to add the same code in NSSound and NSMovie. Add a 
proper filter service for ImageMagik (this one would not be a shell 
script but rather a DO application). And of course to fix all the issues 
listed above.

Hope you have fun with filter services,
Fred

gs.sh
Description: application/shellscript

GSServiceInfo.plist
Description: Text document