After Effects Preview Resolutions and Pixel Bender

Question

Hi,
Hopefully this is a simple fix. I've encountered an issue with PB filters and After Effects's variable preview resolution. Consider this simple kernel:
<languageVersion : 1.0;>
kernel gridTest
<   namespace : "quarterlightpictures.com";
    vendor : "Quarterlight Pictures";
    version : 1;
>
    input image4 src;
    output pixel4 dst;
    void evaluatePixel() {
        float2 coordFloored = floor(outCoord());
        dst.rgb = float3(0.0);
        if(mod(coordFloored.y, 50.0) < 1.0)
            dst.rgb = float3(1.0);
        dst.a = 1.0;
All it does is draw some 1px thick horizontal lines 50 pixels apart. This is fine, of course. However if I set the preview resolution in After Effects to 1/2, the lines are no longer drawn - the comp goes completely black. What I'd expect is the output to be subsampled in AE, and the lines to become 2px thick, but half as bright, which is what happens if I add a Grid effect and do the same.
At 1/3 and 1/4 resolution the lines do appear sporadically - but not everywhere theyr'e supposed to be - and are drawn 3 and 4 pixels thick accordingly.
Does PB work pre-or-post down-res? In other words, does a PB filter run, send its output to AE's comp window and then gets down-ressed for preview (if the resolution isn't full), or does it down-res the dource and pass it to PB? If it's the former then it should just work as I expect. If it's the latter, then are my source dimensions becoming halved, or are my pixel sizes becoming 2x2?
Hope that makes sense. This is causing an issue with a plugin I wrote using PB, with things disappearing when adaptive resolution kicks in.
Thanks,
Christian

Answer 1

I've figured it out.
If you test like so, it works!
     dst.rgb = float3(0.0);
     if(mod(coordFloored.y, 50.0) < pixelSize(src).y)
            dst.rgb = float3(1.0);
        dst.a = 1.0;
Christian