[cairo] Pixman sampling coordinates

[Bill Spitzak]

Bill Spitzak wrote:
> Carl Worth wrote:
> 
>> rotate-image-surface-paint is passing in the no-offset case while
>> failing in the case of a 25x25 offset.
>>
>> Something's really fishy there, because an integer offset should not
>> be changing the sampling behavior.
>>
>> So, chalk another point up for the test suite. But, Bertram, what did
>> we miss in the image sampling code?
> 
> Could this be rint rounding x.5 to the nearest *even* number. Ie if x is 
> odd it rounds up, but if x is even it rounds down.

Another possibility is that regular int() rounding is being done, which 
rounds toward zero. This would cause things less than zero to round 
right, while greater than zero to round left.