[cups.development] document rotation; WAS Re: Access to IPP attributes in filters and backends

[Michael R Sweet]

Jon Peatfield wrote:
> On Thu, 13 Dec 2007, Michael R Sweet wrote:
> 
>> urs-jakob.rueetschi at phz.ch wrote:
>>> I would like to read and modify IPP job attributes from within 
>>> filters and backends. What's the best way to do so? Do I have to use 
>>> httpConnect(), ippWrite() and friends? Is there a simpler / more 
>>> direct method?
>>
>> That is the only supported way to read attributes, however in general
>> filters cannot modify attributes since the job is active.
> 
> Should a filter not be allowed to alter the options seen by later 
> filters to say that they have been acted on already and don't need to 
> still be done?

That's not possible; all of the filters are run in parallel, with the
output from the first filter getting piped into the second, and so
forth.

> Otherwise when (say) a PDF job requests page rotation how does the 
> pdftops tell pstops not to also attempt to rotate the job?

The standard pdftops included with CUPS embeds a cupsRotation comment
that tells pstops what orientation/rotation has been performed.

If you use a different pdftops filter, that information is lost and
you can get double-rotation.

> Currently running cups-1.3.4 on a test server I see PDF jobs submitted 
> from MacOSX with orientation-requested set to 4 (landscape) ending up 
> printed incorrectly rotated (upside down I think 'cos it looks like two 
> sets of 90 degree rotations are being done).
> 
> Manually running pdftops and then pstops with orientation-requested=4 
> shows that each of them seems to do a rotation on the job.  Is this 
> expected?
 > ...

No, this should not happen.

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Michael R Sweet                        Senior Printing System Engineer