[cairo] Copying of clip not working for PS surface

[Fred Kiefer]

Thank you for this explanation. The copy_clip_path would just do the
trick for us, if you could at that to an upcoming cairo release, then
the GNUstep cairo based code could be fully working.

Cheers,
Fred


Vladimir Vukicevic wrote:
> Fred Kiefer wrote:
>> About a week ago I send this mail to the mailing list, but didn't get
>> any reply.
>> What I need to know is if this is intended behaviour and if there is a
>> way to work around it. If necessary, I could provide you with some
>> background information, where and why the copying of the current clip
>> range is needed in GNUstep (We use it to work around another limitation
>> of cairo).
> 
> Unfortunately this is unimplemented behaviour -- the
> copy_clip_rectangle_list stuff only works when the backend implements
> clipping using a region.  The PS surface uses the path directly, and so
> even if the path is a rectangle, it's still stored as a path and not a
> region.  There are two things that could be done here:
> 
> 1) copy_clip_rectangle_list could try to do a tessellation and a region
> extraction if the clip that's set is a path;
> 
> 2) implement a copy_clip_path (since we already have a public way to
> represent a path).
> 
>     - Vlad
> 
>>
>> Cheers,
>> Fred
>>
>>
>> Fred Kiefer wrote:
>>> Is anybody able to explain why the following short program gives the
>>> output "Cairo status 'clip region not representable in desired format'
>>> in copy clip"?
>>>
>>> The same operations work fine when applied to an image surface.
>>>
>>> Thank you
>>> Fred
>>>
>>> #include <stddef.h>
>>> #include <cairo.h>
>>> #include <cairo-ps.h>
>>>
>>> int
>>> main (int argc, const char *argv[])
>>> {
>>>   cairo_status_t status;
>>>   cairo_t *ct;
>>>   cairo_surface_t *surface;
>>>   cairo_rectangle_list_t *clip_rects;
>>>
>>>   surface = cairo_ps_surface_create("test.ps", 100, 100);
>>>   status = cairo_surface_status(surface);
>>>   if (status != CAIRO_STATUS_SUCCESS)
>>>     {
>>>       printf("Cairo status '%s' for surface\n",
>>> cairo_status_to_string(status));
>>>       return 0;
>>>     }
>>>
>>>   ct = cairo_create(surface);
>>>   status = cairo_status(ct);
>>>   if (status != CAIRO_STATUS_SUCCESS)
>>>     {
>>>       printf("Cairo status '%s' for context\n",
>>> cairo_status_to_string(status));
>>>       return 0;
>>>     }
>>>
>>>   cairo_rectangle(ct, 10, 10, 80, 80);
>>>   cairo_clip(ct);
>>>   clip_rects = cairo_copy_clip_rectangle_list(ct);
>>>   status = clip_rects->status;
>>>   if (status != CAIRO_STATUS_SUCCESS)
>>>     {
>>>       printf("Cairo status '%s' in copy clip\n",
>>> cairo_status_to_string(status));
>>>     }
>>>
>>>   cairo_destroy(ct);
>>>   cairo_surface_destroy(surface);
>>> }