io7m-com
Raycasts miss exact matches on boxes
For example:
A box b is placed at (32, 32) of size (64, 64).
A ray is cast from (16, 32) to (256, 32). The ray should intersect b because it passes through 32 on the Y axis, and that's the minimum Y value of b. However, the current implementation misses the intersection.
This appears to be a bug in the calculation of the inverse ray vector. The problem is that given a ray like the above: (16, 32) with direction (1, 0), the inverse vector turns out to be (1, Infinity), which is definitely wrong!
No, this is actually an expected property of the rays. See: https://tavianator.com/fast-branchless-raybounding-box-intersections/
This is actually caused by NaN values appearing in the computation. Covered here: https://tavianator.com/fast-branchless-raybounding-box-intersections-part-2-nans/
Waiting to hear from the author about whether or not anything can be done about this. I can't work it out from the second part of the article.
I cover this in my latest post: https://tavianator.com/2022/ray_box_boundary.html. TLDR:
- tmin = max(min(t1, t2), tmin);
- tmax = min(max(t1, t2), tmax);
+ tmin = min(max(t1, tmin), max(t2, tmin));
+ tmax = max(min(t1, tmax), min(t2, tmax));
...
- return tmin < tmax;
+ return tmin <= tmax;
Ah, thank you!
Sorry for the ridiculous delay in replying. I had no idea this had even been posted (I get far too many GitHub notifications for any human to deal with!). :slightly_smiling_face: