[XRender] Why does scale on x-axis blur on y-axis too?

[Clemens Eisserer]

Hello,

1. When setting a scale only on the x-axis of a 1x10 RGB24 picture,
and using a bilinear filter on the source picture, the result is also
blurred on the y-axis.
When using nearest everything works as expected.
http://picasaweb.google.com/linuxhippy/Transformations/photo#5224017614970060162

When I use RepeatPad instead of RepeatNone the problem is gone, then I
still have the problem mentioned below.
Any idea why RepeatPad helps in this case?


2. The image is still filtered with the non-existing pixels arround
the image on the x-axis which are rendered black:
http://picasaweb.google.com/linuxhippy/Transformations/photo#5224020903104218962

So it more or less filters with pixels which don't belong to the image
itself.  Is it possible to tell XRender to filter only with pixels
that belong to the picture?
I copied the code to: http://pastebin.com/m3b2db21e


Thank you in advance and sorry for nerving with those basic questions,
lg Clemens