A_Blast, how much damage is dealt on collision?

Kzer-Za · Post by **Kzer-Za** » Sat Nov 21, 2020 2:09 am

Does anyone happen to know how exactly A_Blast calculates how much damage is dealt when the affected actor collides with something/someone?

Post by **Gez** » Sat Nov 21, 2020 2:25 am

It's based on the actor's mass.

The collider will inflict damage to the collidee equal to 1 + 1/100th of the collider's mass.

Reciprocally, the collidee will inflict damage to the collider equal to 1/4th of (1+1/100th the collidee's mass).

Code: Select all

	// Check for blasted thing running into another
	if ((tm.thing->flags2 & MF2_BLASTED) && (thing->flags & MF_SHOOTABLE))
	{
		if (!(thing->flags2 & MF2_BOSS) && (thing->flags3 & MF3_ISMONSTER) && !(thing->flags3 & MF3_DONTBLAST))
		{
			// ideally this should take the mass factor into account
			thing->Vel += tm.thing->Vel.XY();
			if (fabs(thing->Vel.X) + fabs(thing->Vel.Y) > 3.)
			{
				int newdam;
				damage = (tm.thing->Mass / 100) + 1;
				newdam = P_DamageMobj(thing, tm.thing, tm.thing, damage, tm.thing->DamageType);
				P_TraceBleed(newdam > 0 ? newdam : damage, thing, tm.thing);
				damage = (thing->Mass / 100) + 1;
				newdam = P_DamageMobj(tm.thing, thing, thing, damage >> 2, tm.thing->DamageType);
				P_TraceBleed(newdam > 0 ? newdam : damage, tm.thing, thing);
			}
			return false;
		}
}

tm.thing is the collider (blasted thing) and thing is the collidee (the impact target for the blasted thing).

Also when a thing is blasted into a wall, it takes damage equal to its own mass divided by 32:

Code: Select all

				if (tm.thing->flags2 & MF2_BLASTED)
				{
					P_DamageMobj(tm.thing, NULL, NULL, tm.thing->Mass >> 5, NAME_Melee);
}

(The ">>" symbol is a right bitshift, >>5 means bits are shifted right by five points, which amounts to dividing by 2 to the power of 5.)

Kzer-Za · Post by **Kzer-Za** » Sat Nov 21, 2020 2:28 am

Thanks!

Kzer-Za · Post by **Kzer-Za** » Sat Nov 21, 2020 2:46 am

Hm, I have just tested it on Ettins and something seems off. The Ettin that was blasted into another Ettin suffers 10 damage, and the Ettin that was standing when the first one was blasted into him suffers 4 damage. And when they are blasted into architecture the damage seems to be rather random (though almost always (but not always) divisible by 5), or I can't understand the pattern: the distance seems to have no significance.

Kzer-Za · Post by **Kzer-Za** » Sat Nov 21, 2020 3:25 am

It appears I have found a bug (though I don't understand what in the code is causing it), or even two.

1. The damage to both the collider and the collidee is applied 2 times. If you blast the victim into architecture, the damage is applied 2 times at the minimum, sometimes many times more (more than ten times).

2. The collider and collidee become "entangled". After you have collided one into another once, you can blast one while the other is nowhere near your field of view, and the other gets blasted too.

I think I need to report it.

ZDoom