If you want more specifics, sloped FOFs are to blame it turns out: sometimes the bottom of an FOF wall blocking a segment of an in-level wall column can be considered ABOVE the top part of the FOF there (yikes), and then the dc_y* values go offscreen, and then BOOM
Compiling errors fixed in this commit:
* Various cases of mixed declaration and statement code
* Implicit declaration of slope functions (read: you forgot to put "include "p_slopes.h" in MORE than a few places)
* an odd case of a bad fixed_t to float typecase, cause by using P_GetZAt directly inside FIXED_TO_FLOAT
* a few minor cases of bad unsigned-signed comparisons
* no prototypes for some of the new slope functions. For goodness sake Red, this is basic stuff!
Monster Iestyn