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.

How to test it:




Hope you have fun with filter services,
Fred

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

gs.sh
Description: application/shellscript

{
  NSServices = (
    {
      NSFilter = GhostScript;
      NSInputMechanism = NSUnixStdio;
      NSPortName = "/home/fred/GNUstep/Examples/gs.sh";
      NSSendTypes = (
        NSTypedFilenamesPboardType:ps, NSTypedFilenamesPboardType:eps, 
NSTypedFilenamesPboardType:pdf
      );
      NSReturnTypes = (
        NSTypedFileContentsPboardType:tiff
      );
    },
   );
}

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