Damage
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The contents of this article are outdated, confusing or constructed in a discussion format. Possibly due to alien mind control. Please help fight the alien menace by updating or correcting the information on this page. |
Overview
Damage in the world of X-COM follows a series of rules that define how damage is dealt and taken. This article will explain the basics of how damage is done.
Definitions
For the purpose of this article, damage will be differentiated into two main categories. Firearm and Explosive. There is also Incendiary, but this will be covered elsewhere.
- Firearm
- This damage type covers most damage types as per the table below.
| Enemy Unknown/UFO Defense | Terror From The Deep |
|---|---|
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- Explosive
- This damage type covers all weapons that use the High Explosive damage type, from grenades to rockets.
- Incendiary
- This covers Incendiary/Phosphor damage. Because this type of damage follows its own complex damage model, it will not be covered in great detail here. Refer to its article for the particulars.
The damage categories can be further subdivided into three target categories, unit, terrain, and object.
- Unit
- Cover all actors in the field from X-COM units to aliens to tanks.
- Terrain
- Cover all floors, ceilings, walls and any other fixtures that are contained in a tile such as light poles, post boxes, tables, 'middle' walls, oil drums, etc.
- Object
- Covers all items that can be picked up off the ground and manipulated by units, including weapons and bodies.
Formula
In its purest form, the amount of damage target will take from a weapon is:
Damage to Target = Damage - Armour
The Damage component, being the main subject of this article, is broken down into the following formula:
Damage = Base Weapon Damage × Random Weapon Range × Damage Modifier
If the bullet does negative or zero damage: No damage is done. If the target is an alien controlled unit you will still get Firing Accuracy experience if it did hit.
If the bullet does damage (aka Penetrating Damage): Units will have health deducted while terrain or objects will be destroyed.
Against units there are additional effects such as adding critical wounds, stun damage, morale loss and a chance that the armour plate that it struck will deteriorate by a few points, as shown below.
Let's expand on the variables a bit:
- Base Weapon Damage
- This is the number that you see for the weapon in the UFOpaedia.
- Random Weapon Range
- This is the random number roll that alters how much damage is to be dealt. For firearms, a value between 0% and 200% is rolled while explosives will perform a 50% to 150% roll. See the next section.
- Damage Modifier
- This is a percentage value that controls how weak or how strong the bullet will affect certain classes of targets.
- Armour
- The armour section the bullet hit. Armour is pure damage reduction.
Damage Ranges
When dealing damage, the game first performs a random dice roll to determine what percentage of the weapon damage is to be dealt to the target. This variability allows a simple simulation of critical hits that defeat the target instantly or creates dud shots that hit but are absorbed or deflected by the target's armour resulting in no damage.
This random range varies depending on the weapon and target category.
| Target \ Damage | Firearms | Explosive |
|---|---|---|
| Units | 0 - 200% | 50% - 150% |
| Terrain | 25% - 75% | 50% |
| Objects | n/a* | 100%# |
* Objects are only damaged by high explosives.
# Objects technically use the Unit damage ranges to determine how much damage to compare against.
In reality, all of the damages listed in the UFOpaedia are the averages for the weapons. Note that the doubling of Firearm damage is done before the damage modifiers are applied.
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In TFTD, the listed weapon damage in the UFOpaedia is still the average damage caused, but the difference from UFO is that random weapon damage is rolled twice and averaged, which produces values which are more often closer to the average) |
Damage Modifiers
Damage Modifier is term coined through discussions on X-COM web forums and used on this wiki to describe resistance or vulnerabilities of the target to a particular damage type.
Units are typically divided into various unit classes. While many unit classes are unique to each unit, there are some groups that share the same class, mainly humanoids like civilians, unarmoured X-COM units and Sectoids/Aquatoids.
Each class has a table of percentage value that detail how vulnerable or resistant they are to every damage type in the game. These percentages modify the total amount of damage that is dealt.
Naturally, a value of 100% means that target takes normal damage from the weapon. A value over 100 means it takes more damage, and a value under 100 takes less damage.
See the main Damage Modifiers or Damage Modifiers (TFTD) for data tables of damage modifiers for the various unit classes. For another way to view the same info, see this.
Effects of Armour
Armour is the value protective plating of any one of the sides of the target that the bullet is hitting. It differs from the damage modifier in that all it does is reduce the amount damage after the total damage has been calculated.
For ballistic projectiles, units can be hit from the Front, Rear, Left and Right armour.
Explosive damage will target Under armour if the target is at or standing right next to the very centre of an explosion from an area-effect weapon. For all other ranges in the blast radius are treated as directional damage from the centre of the explosion.
Terrain and Objects do not have hit-points and rely solely on their fixed armour levels. If damage exceeds their armour, they are destroyed, otherwise they survive.
When terrain is destroyed, it is replaced by the next 'damaged' tile in its sequence. When all available tiles are destroyed, only a regular earth tile will remain on the ground. In the case of tiles suspended in the air, nothing will remain or in some cases the last damaged tile that is not solid.
Objects are destroyed completely when their armour is exceeded by damage. See Object Destruction for the specifics.
Example
Adapted from Zombie's kindly example:
Scenario: Beginner level Muton mission. Your soldier is carrying a normal Pistol and you want to know what is the chance that a Muton Soldier's front armor will absorb a direct hit without lowering health.
Vitals: Muton Soldier front armor = 10 Muton Soldier health = 125 Muton susceptibility to Armor Piercing ammo = 60% Pistol listed power = 26 (average)
Calculation:
Max damage for a Pistol against a Muton is lowered due to susceptibility:
Modified max damage = INT(26 * 2 * 60 / 100)
= INT(52 * 60 / 100)
= INT(3120 / 100)
= INT(31.2)
= 31
where 2 is the max modifier (200% of UFOpaedia listed power) and 60/100 is the damage modifier (60%)
The range of values the Pistol can deal is 0 to 31 points of damage (or a range of 32 different values). The equation's steps are shown because XCOM's math sometimes leads to slightly unexpected values in subsequent steps.
The Muton Soldier has a front armor rating of 10. It will absorb up to this much damage without changing health. In other words, it will negate the first 10 points of damage a Pistol can dish out (0-10; 11 possible values). Since the Pistol has a range of 32 possible values, the probability that a direct hit will be blocked by Muton armor is simply 11 / 32 = 34.4%.
Okay, say you want to know the probability of doing damage to a Muton's health. The pistol still has 32 values, but instead of absorption we want penetration. 10 points of damage is absorbed, so we need at least 11 to penetrate. 32 - 11 = 21 values which will breach. 21 / 32 = 65.6%.
21 is also the maximum number of damage points which might be deducted from the Muton's health. Assuming the Muton was initially uninjured, in the worst case (for him!) he will have an ending health of 125 - 21 = 104.
On average, there will be 15.5 damage dealt (0-31). Then armor (10) reduces this to an actual (penetrating) average damage of 7.22. (It's not simply 15.5-10=5.5 because initial damage that's less than ten becomes zero penetrating damage, not negative penetrating damage. The removal of these negative values causes the expected average to rise, as it were.)
If you need precision while testing, note that the game applies truncation after making its damage roll. It does not first determine the maximum (including damage modifiers), and then roll randomly/evenly from 0 up to the maximum, per se. To wit: if you hack a pistol to an average damage strength of 1, there would not be an overall roll of 0 to a maximum of 1 (with average damage of 0.5) as might be implied from the Muton-versus-AP example above. Instead, there is a roll of 0, 1, or 2, to which the .6 modifier is applied. Only a roll of 2 results in non-zero damage (INT(2x60/100)= INT(1.2)= 1), and the Muton only takes an average of 0.33 damage, not 0.5. Usually this effect is insignificant relative to the large damage values found in the game, but it could matter in testing situations involving very low damage strengths. It also means you need to take into account all possible values versus individual truncation effects, if you want an ultra-precise listing of e.g. how often armor is breached.
Penetrating Damage vs Armor Damage, Health Damage and Fatal Wounds
Penetrating Damage is simply the final, modified damage (modified by all susceptibility and vulnerability factors), minus the current armor level on the relevant facing of the target.
When there is Penetrating Damage (i.e., damage is >0 and not all blocked by armor), Health and Armor Damage occurs, i.e. Health and Armor levels are reduced.
Health Damage - the reduction in the target's current Health - is simply equal to Penetrating Damage. Health is allowed to go to negative values (negative values are only really relevant to Stun damage - otherwise, dead is dead).
Health Damage, in turn, dictates the probability of suffering Fatal Wounds (normally just for XCom soldiers):
- Between 1 to 10 points of Health Damage, the chance of Fatal Wounds increases more or less linearly from 9% to 90%
- There is 100% chance of Fatal Wounds if taking 11 or more points of Health Damage
- Whenever a target affected by Fatal Wounds, there is always an equal chance of 1, 2 or 3 Fatal Wounds, regardless of Health damage sustained.
For more information on Health Damage versus Fatal Wounds, see Fatal_Wounds#Probability_of_Fatal_Wounds.
Armor Damage - the amount that the target's current Armor level is reduced by, on the impacted facing - is equal to one tenth of Penetrating Damage, rounded up (to a maximum of the current Armor Level, since it can't go below zero). This means that an opponent who is almost invulnerable to your weapons, will slowly become more vulnerable, with every successful penetrating hit.
Note that Stun/Freeze damage, and Fire damage, do not reduce Armour level, and do not cause Fatal Wounds.
Relationship Between Health and Armor Damage
For situations where Penetrating Damage is less than the current Armor level, Health and Armor Damage have a very simple relationship to each other:
Health Damage = 10 * Armor Damage, minus 1 to 10
Or the other way around:
Armor Damage = INT( Health Damage / 10 ) + 1
In table form:
Armor Health Damage
Damage Min Max
0 0 0
1 1 9
2 10 19
3 20 29
4 30 39
5 40 49
6 50 59
7 60 69
8 70 79
9 80 89
etc.
Of course, this assumes armor is not zeroed out by the hit. Also note that you will always have armor damage if you have health damage and vice-versa, if there was damage penetration. Stated another way, you will never have armor damage if you don't have health damage (i.e., when there is insufficient damage to breach the armor).
You will see this health/armor relationship if you watch damage from individual hits. However, the relationship is muddied if you only look at a unit after a number of hits (or, of course, if armor is broken through). The most extreme example would be if a unit were hit with e.g. five hits of 1 penetrating damage point each. The unit would have 5 health damage and 5 armor damage, which would appear contrary to the above table.
This relationship has been been tested for a wide variety of explosions and some light weapons vs. Mutons, and some hits on soldiers. It has not otherwise been widely tested, but is presumed true unless/until found otherwise.
As stated, the above is for damage that penetrates. It is possible for hits (guns or explosions) to do zero damage. This happens on the rare occasion that a weapon damage roll is actually zero, or, much more commonly, when armor has blocked all the damage. You still get an experience point toward Firing Accuracy if damage fails to penetrate. You only have to hit the target(s) to get Firing experience; there doesn't have to be damage.