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tunabrain / tantalum

WebGL 2D Light Transport
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precision issue #1

Closed fernLightning closed 8 years ago

fernLightning commented 8 years ago

I found that 'Cardoid' scene would leak many rays into the inner box, and that in other scenes I was seeing occasional rays pass through lenses (via the circular part) unaffected.

I was able to resolve the issue by adding a normalise() into the unPackRay() func, i.e

  ...
  dir = normalize(dir);
  return Ray(pos, dir, 1.0/dir, sign(dir));
}

osx 10.11.1 - Intel HD Graphics 5000 - safari 9.01 (possibly a a symptom of the graphics card as an AMD based mac had no issue).

tunabrain commented 8 years ago

Oh, interesting! I think this may be an issue with the NaN-prevention, which can change the length of the direction. I hadn't considered this.

I just pushed your proposed fix, let me know whether that removes the problem.

Thanks!

fernLightning commented 8 years ago

yes, that fixes the problem.

fyi: removing the NaN-prevention code had no notable effect, and also toying with sphereSegmentIntersect() code (e.g. subtracting a small offset from the times) wasn't reliable or added other artifacts into the scene.

tunabrain commented 8 years ago

The NaN prevention is an odd one; I'm not entirely sure why it fixes problems, but I was in contact with a few people on Intel cards that experienced problems with black horizontal or vertical lines that would appear after a while and permanently corrupt the image.

From that description it did seem likely that a division by a zero directional component was causing issues somewhere, even though all relevant code guards against that. Debugging funky shader compilers remotely was difficult, so I just added code permutations until they reported it as fixed :)

In any case, thanks for reporting back.