Projectiles can activate Doom linetype 24 G1 Raise Floor

[simc]

In GZDoom on Doom/Boom and Hexen-Doom format maps passing projectiles (such as monster fireballs or player's rockets) can trigger Doom linetype "24 G1 Floor Raise to Lowest Ceiling" on 2s lines. This doesn't happen in Chocolate Doom. In there it works only for player hitscan attacks. On Doom/Boom format maps hitscan monster attacks do not trigger this action in GZDoom.

Furthermore, not sure where the fault is, if the same Doom/Boom format map is converted to Hexen-Doom format with zwadconv.exe the action is changed to "238 Floor Raise to Lowest Ceiling" (tag, speed:8, trigger: Projectile hits, Monster Activates: not selected) - and now also monster hitscan attacks will trigger this action in GZDoom.

If the Hexen-Doom format map is converted to UDMF (Map Options change in UDB) monster hitscan attacks and projectiles by both the player and monsters will no longer trigger it. But if the Monster activates flag is turned on then monster hitscan attacks will trigger it..

Here are three test wads for Doom2 map01. One for each format: Doom, Hexen-Doom and UDMF. The Hexen-Doom wad is converted from the Doom/Boom wad with zwadconv.exe. The UDMF wad is converted from the Hexen-Doom wad with UDB Map Options change. The imp, hell knight and chain gunner are behind a monster blocking line. The action line is marked on the floor. Just wait until the monsters attack.

[Professor Hastig]

You have to be aware of something here:

When ZDoom initially introduced Hexen map format it made the unwise decision to alter trigger semantics.
This has long been fixed in the engine for both original Doom/Boom format, original Hexen and UDMF, but since so many ZDoom-Hexen format maps depend on these altered semantics the default for these had to remain what ZDoom originally did.
To get proper trigger semantics for ZDoom-Hexen format maps you have to add 'strictlineactivation' to your MAPINFO.

Player projectiles being able to activate this trigger seems like a deliberate change. It makes sense that all weapons can trigger these lines to avoid switching back and forth.

[simc]

You have to be aware of something here:

To get proper trigger semantics for ZDoom-Hexen format maps you have to add 'strictlineactivation' to your MAPINFO.

Indeed, but it seems that with strictmonsteractivation also "GZDoom: Doom (Hexen format)" maps behave exactly like Doom/Boom format maps. The flying monster projectiles do trigger the action when it flies over the action line. If the projectile only collides to the actionline it will not trigger it. To clarify:

Attacks that can trigger the line type in GZDoom.
Doom/Boom format map: 24: G1 Floor Raise to Lowest Ceiling
Doom/Hexen format map 238 Floor Raise to Lowest Ceiling", projectile hit w/strictmonsteractivation (further details in the original post)
------------------------------------------------------------------------- | player | player | monster | monster | | hitscan | projectile | hitscan | projectile | ------------------------------------------------------------------------- one sided wall | yes | yes | no | no | two sided wall, hits | yes | yes | no | no | two sided wall, fly over | yes | yes | no | * YES * | -------------------------------------------------------------------------