How does CUPS scheduler decide next filter / backend?

[Michael Sweet]

anonymous wrote:
> When CUPS scheduler calculates cost of filters, how does it know what file 
> format (PCL/PS) backend is expecting?

It maps everything to the printers/name pseudo-type; the mapping
comes from the cupsFilter lines in the PPD file or an internal
mapping of application/vnd.cups-postscript to printers/name if there
are no cupsFilter lines in the PPD file.

> Basically I want to print PCL files to my PCL printer, but I don't want to 
> create a special raw queue for that. (It doesn't make sense, ps, text, 
> image, pdf all send to the same queue, why pcl file need to sent to a 
> special queue?)
> 
> I want to create a filter, and added an entry in *cupsFilter in the PPD 
> file. How can CUPS know my pcl2pcl filter is the last filter?

Define the PCL file type, and then use:

     *cupsFilter: "mime/type 0 pcl2pcl"

to pass those files through your filter.

> Another question is when pipe a couple of filters together, how could a 
> filter know which / whether the user option has been processed?

It is basically implied by the output content type;
application/vnd.cups-postscript and application/vnd.cups-raster
have all options applied.  Filters that produce them have to
ensure that the "universal" options are applied.

-- 
______________________________________________________________________
Michael Sweet, Easy Software Products           mike at easysw dot com
Internet `Printing and Publishing Software       http://www.easysw.com