[cairo] Help with PDF output from painting surfaces

[Andrea Canciani]

On Mon, Nov 14, 2011 at 5:01 PM, Cope, Phil (GE Energy)
<phil1.cope at ge.com> wrote:
> 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.

More than antialiasing, I would guess that your problem is CAIRO_EXTEND_NONE.
Can you check if setting the extend mode to PAD solves your problem?
(You will need to fill a rectangle, if you use a PAD-extended source).

Andrea

>
>
>
> 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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>