Things are lit differently by Boom's floor/ceiling light level transfers (213 & 261) depending on port and complevel

[elf-alchemist]

Test WAD: transferred_sector_light.zip

It's time for Undocumented MBF Changes™

Alongside the fake heights transfer (242), Boom also introduced two separate line specials that individually transfer floor and ceiling light levels (213 and 261) onto a tagged sector. Normally, in Boom and CL9, any Things present in said sector will be lit according to the sector's normal light level. MBF, however, changed this behavior to decide a Thing's light level using the average of the transferred floor and ceiling light levels, instead.

The MBF behavior of projecting sprites with the average of the transferred light levels is highly dislike by mappers, in general, given the lack of control provided by it. The ideal solution is to rollback the behavior to it's original Boom

Woof/DSDA on -complevel 09 -- real sector light

Woof/DSDA on -complevel 11, or later -- average transferred light

Eternity -- average transferred light

Helion -- average transferred light

Odamex -- average transferred light

GZDoom -- floor light only

EDGE-Classic -- real sector light

KEX on boom2.02 -- real sector light

KEX on complevel 09, or later -- floor light only

[haleyjd]

I believe we should be focused on providing this as an option (either globally through mapinfo or with some new line type) for new maps and not changing the behavior of existing ones. When behaving like MBF, EE should behave like MBF in this regard. Likewise for Boom, which is currently lost behavior.

[XaserAcheron]

Quick correction for the OP: The Kex cl9+ behavior is "floor light only", rather than "average transferred light." Probably a transcription error, since the screenshots match the reported behavior.

There are two layers to fixing this: the first is making the existing behavior consistent across ports (the behavior on existing maps is effectively undefined right now), and the second is introducing some means of controlling it. Since this is tied to complevel in several of the ports (which matches historically, since this was an MBF change), it makes sense to expose this as an OPTIONS lump thing and fix up the default to be nicer in the next MBFxx.

[elf-alchemist]

Relevant:
kraflab/mbf21#6
fabiangreffrath/woof#2393
kraflab/dsda-doom#820
team-eternity/eternity#740
odamex/odamex#1499