Is displacement supposed to be working? I have an error in the following image. I don't know if it's my rib/shader or a pixie bug:
Exposure 1.0 2.2
Display "test.tif" "file" "rgba"
Format 508 380 1.0
Projection "perspective" "fov" [ 90 ]
Translate 0 1 5
Rotate 45 1 0 0
Sphere 3.0 -3.0 3.0 360.0
float amp = 0.1 * sin(t*20*PI);
amp += 0.1 * sin(s*20*PI);
P += amp * normalize(N);
N = calculatenormal(P);
The problem areas are at the bottom of the sphere and the upper left area of the sphere.
Dan, I think the easiest and fastest you could do is testing the same input with Aqsis and/or 3delight and compare that output to Pixie's.
At least you could see if the bug is related to your stuff or to Pixie internals.
Hi, thank you for responding. I have rendered the given scene with Aqsis, and it shows very small sliver-shaped artifacts in other parts of the image but the areas that look bad in Pixie look fine with Aqsis. The bad areas in Pixie are fairly large rectangular patches on the surface.
You need to set the displacement bound for the sphere, so that Pixie knows how much your shader will displace it. This is the same in PRMan (though the default displacement bound may be different).
Add the following lines to your rib before the sphere,
Attribute "displacementbound" "sphere" 
Attribute "displacementbound" "coordinatesystem" "current"
Note that 30 is an arbitrary number I found to work, rather than the correct figure. It's generally best to keep the bound as tight as possible for efficiency reasons.
Hope this helps
Yes, I see that fixed it. Sorry it was not a Pixie-related error. Thanks for pointing this out for me.