Help me decipher this snippet of code

[na85]

Trying to update some old, poorly commented code from (believe it or not) 093 to the newest version. Having trouble understanding what exactly this function is doing:

Code: Select all

function IsImmunedFromThisDamageType( who, byref dmg, attack_type )

	var immunities := GetObjProperty( who, PROPID_MOBILE_ATTACK_TYPE_IMMUNITIES );
	if( !immunities )
		return 0;
	endif
	
	if( attack_type & DMGID_NO_RESIST )
		return 0;
	endif

	var attack_amount	:= 0;
	var is_immuned_amount	:= 0;      
	foreach bit in { DMGID_FIRE, DMGID_AIR, DMGID_EARTH, DMGID_WATER, DMGID_NECRO, DMGID_HOLY, DMGID_POISON, DMGID_ACID, DMGID_PHYSICAL, DMGID_MAGIC, DMGID_ASTRAL }
		if( attack_type & bit )
			attack_amount := attack_amount + 1;
			if( immunities & bit )
				is_immuned_amount := is_immuned_amount + 1;
			endif
		endif
	endforeach
	
	if( !attack_amount || attack_amount = is_immuned_amount )
		return 1;
	else
		dmg := Cint( dmg * Cint(attack_amount-is_immuned_amount) / attack_amount );
		return 0;
	endif
	
endfunction

-attack_type is an integer that gets set by the DealDamage function in a hitscript, defaulting to 0x0100 to represent physical damage. More on this below.
-PROPID_MOBILE_ATTACK_TYPE_IMMUNITIES is an integer stored in a CProp on the mobile. That CProp is either i256 or i639. No other values appear in any npc definitions.

At the top of the function there exist some declarations:

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const DMGID_FIRE	:= 0x0001;
const DMGID_AIR		:= 0x0002;
const DMGID_EARTH	:= 0x0004;
const DMGID_WATER	:= 0x0008;
const DMGID_NECRO	:= 0x0010;
const DMGID_HOLY	:= 0x0020;
const DMGID_POISON	:= 0x0040;
const DMGID_ACID	:= 0x0080;
const DMGID_PHYSICAL	:= 0x0100;
const DMGID_MAGIC	:= 0x0200;
const DMGID_ASTRAL	:= 0x0400;
const DMGID_NO_RESIST	:= 0x0800;

At first it seemed to make sense because on most mobiles with that cprop, its value is i256 which in hex is of course 0x100 which seems to correspond to a monster being immune to physical damage. However i639 in hex is 0x27f which seems like an oddball value and certainly doesn't appear in the above chart.

These constants are also the values which the variable attack_type can take.

[OWHorus]

<...>

Code: Select all

const DMGID_FIRE	:= 0x0001;
const DMGID_AIR		:= 0x0002;
const DMGID_EARTH	:= 0x0004;
const DMGID_WATER	:= 0x0008;
const DMGID_NECRO	:= 0x0010;
const DMGID_HOLY	:= 0x0020;
const DMGID_POISON	:= 0x0040;
const DMGID_ACID	:= 0x0080;
const DMGID_PHYSICAL	:= 0x0100;
const DMGID_MAGIC	:= 0x0200;
const DMGID_ASTRAL	:= 0x0400;
const DMGID_NO_RESIST	:= 0x0800;

At first it seemed to make sense because on most mobiles with that cprop, its value is i256 which in hex is of course 0x100 which seems to correspond to a monster being immune to physical damage. However i639 in hex is 0x27f which seems like an oddball value and certainly doesn't appear in the above chart.

These constants are also the values which the variable attack_type can take.

0x27f := DMGID_FIRE + DMGID_AIR + DMGID_EARTH + DMGID_WATER + DMGID_NECRO + DMGID_HOLY + DMGID_POISON + DMGID_MAGIC;

Where's the problem ?

This guy is immune against elemental and magic damage, but not against acid, physical and astral damage.

OWHorus

[na85]

Shit...

That makes sense, can't believe I couldn't figure that out.

Thanks!