[cairo] Shifting (scrolling) a translucent surface?

[Nis Martensen]

Am 09.03.2012 20:07, schrieb Stefan Salewski:
>> And, I wonder how the OPERATOR_CLEAR depends
>> on the source surface?
> 
> OK, from 
> 
> http://permalink.gmane.org/gmane.comp.lib.cairo/21625
> 
> we have
> 
>> (Please notice that setting the source is useless whenever the operator
>> is CLEAR,
> 
> This is true from my observation.
> 
> But from 
> 
> http://www.cairographics.org/operators/
> 
> we have
> 
>> CAIRO_OPERATOR_CLEAR
>> The effect of the CLEAR operator depends on the interpretation of the
>> source.

This sentence means that the result of the CLEAR operator would differ
between bounded and unbounded intepretation of the source (together with
the mask). It does not imply that the content of the source matters.

Regards,
 Nis