Custom enemy attacks no longer heal players

[lizardcommando]

I was told that I should report this by one of the mods so here it goes:

I remember that in older versions of ZDoom and GZdoom, in order to make enemy attacks and projectiles heal the player, all you had to do was change the "Damage" flag to a negative number. Now it seems like that no longer works. This is a feature that is needed for a small mod I created.

Is this a bug or was this intentionally removed?

[ZzZombo]

Why can't you heal with more conventional means? Like, givin' a health pack for the lazy, or using more direct approaches?

[lizardcommando]

It was for a mod I created a while ago. The Pain Elemental's new attack purposely healed players by shooting a fireball that heals players by 5 HP.

[Graf Zahl]

This was changed because dealing negative damage is totally undefined behavior. If it worked it was by happenstance but even then it tended to do things that were just wrong.

[Blue Shadow]

But there is an explicit code for this, for projectiles only anyways, in PIT_CheckThing.

[Graf Zahl]

The relevant check is in P_DamageMobj.At the end of the day the damage infliction code cannot handle negative values. It has always been undefined behavior but some more recent changes made it impossible to keep this case working.

[Matt]

Can't there be a check added to the beginning of DamageMobj to deal with negatives? There've got to be a lot of old (or not even necessarily that old) mods that were written on the assumption that this would work.

[Graf Zahl]

There is a check at the beginning to exit if the value is negative. I haven't tracked down the reason but rest assured, it was necessary because some changes to that function could no longer handle it.