Help with PDF output from painting surfaces

Hello, I have a problem with PDF output. I have a system that can
potentially render a huge image (e.g. a satellite photography) It does
this by tiling the image and sending the tiles to Cairo which are then
painted as source.

 

When outputting to PDF there is an issue illustrated by the screengrabs
of Adobe Reader displaying the Cairo output (see links below).  The
first is fine, but the second, which is the same data (approximately)
rotated through 45deg. The third is a zoomed in area of the previous.
The obvious problem is what looks like antialiasing on the edge of the
tiles which is manifesting itself as diagonal lines on the boundaries of
the tiles. 

 

I set 

 

cairo_set_antialias(ctxt, CAIRO_ANTIALIAS_NONE); 

 

while drawing these tiles, I also tried 

 

cairo_set_operator(ctxt, CAIRO_OPERATOR_SOURCE); 

 

(rather than _OVER) but this had bizarre and unwanted effects on the
screen drawing. 

 

Any hints as to how I can remove these artefacts would be much
appreciated, I'm using 1.10.2 

 

Unrotated:

http://s10.postimage.org/p0jf9u0cp/cairo_0deg.png

 

Rotated at 45 deg:

http://s7.postimage.org/4zwv1z697/cairo_45deg.png

 

Above PDF zoomed in:

http://s9.postimage.org/ra6wl28fj/cairo_45deg_zoomed.png

 

 

Cheers

 

Phil Cope

Senior Software Engineer (GE Energy: SSG)

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