[cairo] misc. cairo_t questions

Roger Davis rbd at soest.hawaii.edu
Thu Apr 12 13:00:38 PDT 2012

Hi Uri,

Thanks for your help! One followup question:

>> (3) It seems like almost all of the cairo_set...(), etc., functions 
>>return void. Is there a standard behavior in place to handle bad 
>>arguments to these calls, or other error conditions?
>Yes. If some object gets in an error condition, this error condition is 
>sticky. You can not un-error something afterwards. To get this error 
>flag, there are cairo_status(), cairo_surface_status(), 
>cairo_pattern_status(), ....

I like to be reasonably rigorous in error checking (and am extremely 
averse to allowing situations that could result in a core dump), but it 
does seem like overkill to do a cairo_status() after every single change 
to a context or after every drawing operation. Are there certain 
operations to contexts or surfaces in particular which are unusually prone 
to error generation, especially errors which might ultimately lead to a 
core dump, which it would be useful to check via cairo_???_status()? By 
the way, checking status after cairo_select_font_face(cr, 
"NonexistentFont" ...) doesn't yield any abnormal error code, so I'm 
wondering when these functions might actually return useful information. 
Perhaps this particular case is non-representative since it is, as you 
say, from the toy API.



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