I often keep seeing thin blank lines on my objects when using shadows. I am not sure what causes this, but I remember there was some option somewhere to correct it.
You might try adjusting the bias setting for the lamp casting the shadows.
The cause of that problem is rather involved, but has to do with the fact that shadow buffers (by their nature) only store a single depth for each pixel of the buffer, and each pixel represents a finite area, and not a single point.
In short, it is an aliasing artifact in (for lack of a better term) “shadow space”.
The easiest solution would be to increase the bias. Another possible solution would be to increase the “clipEnd” of the light source or decrease the “clipStart” (which will, indirectly, have the same effect as increasing the bias).
If anyone wants a more in-depth explination, let me know. Knowing how shadow buffers work can help a lot in being able to set them up to look right.
increasing the buffer size or the number of samples might help too.
Martin
Cessen yes, I would like to read an article on how/why it happens. I see this a lot and it would help to understand it more.