Difference between revisions of "Chance to Hit (EU2012)"
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− | {{tocright}}In ''[[Enemy_Unknown_(EU2012)|XCOM: Enemy Unknown]]'', the chance that any given shot will land on your target is based on the sum total of a number of variables. Some work for you, some work against you, but all are additive: if you're told that shiny new rifle gives you a +10 Aim, then indeed your final chance to hit simply goes up by 10% when you're using it. Understanding | + | {{tocright}}In ''[[Enemy_Unknown_(EU2012)|XCOM: Enemy Unknown]]'', the chance that any given shot will land on your target is based on the sum total of a number of variables. Some work for you, some work against you, but all are additive: if you're told that shiny new rifle gives you a +10 Aim, then indeed your final chance to hit simply goes up by 10% when you're using it. Understanding this [[Gameplay_Mechanics_(EU2012)|game mechanic]] will help you determine whether a tile is worth moving to, whereas weighing up the chance to hit a target against the amount of [[Damage_(EU2012)|damage]] you might deal to it is useful when considering taking a defensive action instead. |
− | ''' | + | '''Aim''' (or '''Attack''') is the base statistic each unit has which accounts for the bulk of its accuracy in battle. For [[Soldiers (EU2012)|XCOM units]], this goes up at a set rate based on [[Soldiers_(EU2012)#Ranks|rank]] and [[Classes_(EU2012)|class]], whereas for [[Alien_Life_Forms_(EU2012)|aliens]] it's determined by their race and the [[Difficulty_(EU2012)|difficulty level]]. |
− | '''Defence''', on the other hand, is the statistic which lowers each unit's chance to ''be'' hit. Your units may improve their base defence stat by donning certain forms of [[Armor_(EU2012)|armour]] (keeping in mind that most only grant additional hitpoints, lessoning the ''effects'' of damage, rather then your chance to avoid it altogether). Some alien races have an innate defensive bonus which is further increased on higher difficulties. | + | '''Defence''', on the other hand, is the statistic which lowers each unit's chance to ''be'' hit. Your units may improve their base defence stat pre-battle by donning certain forms of [[Armor_(EU2012)|armour]] (keeping in mind that most only grant additional hitpoints, lessoning the ''effects'' of damage, rather then your chance to avoid it altogether). Some alien races have an innate defensive bonus which is further increased on higher difficulties. |
In addition, units may source additional aim/defence bonuses from soldier perks, terrain factors and equipment, [[Cover_(EU2012)|cover]] being one of the most important examples. | In addition, units may source additional aim/defence bonuses from soldier perks, terrain factors and equipment, [[Cover_(EU2012)|cover]] being one of the most important examples. | ||
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In addition to their base stats, each [[Classes_(EU2012)|class]] may choose from a variety of perks which can potentially improve accuracy, decrease it in exchange for another bonus, raise their defence, or affect the aim/defence values of other units in play: | In addition to their base stats, each [[Classes_(EU2012)|class]] may choose from a variety of perks which can potentially improve accuracy, decrease it in exchange for another bonus, raise their defence, or affect the aim/defence values of other units in play: | ||
+ | {| class="wikitable" width="100%" | ||
+ | |- | ||
+ | ! | ||
===[[File: CLASS ASSAULT.png|left|24px]]'''[[Assault (EU2012)|Assaults]]'''=== | ===[[File: CLASS ASSAULT.png|left|24px]]'''[[Assault (EU2012)|Assaults]]'''=== | ||
− | + | |- | |
− | The Assault class sports moderate accuracy, but their shotguns grant huge bonuses at near range - and they're very good at closing the distance. At distances further then ten tiles, their pistols (or perhaps rifles, if equipped) make for more reliable damage, albeit somewhat reduced in power. They can acquire abilities that improve their defence when up in the alien's faces. | + | |The [[Assault (EU2012)|Assault]] class sports moderate accuracy, but their shotguns grant huge bonuses at near range - and they're very good at closing the distance. At distances further then ten tiles, their pistols (or perhaps rifles, if equipped) make for more reliable damage, albeit somewhat reduced in power. They can acquire abilities that improve their defence when up in the alien's faces. |
<center> | <center> | ||
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*<font color=blue>Aggression</font>: A +10% [[#Critical Hits|crit chance]] bonus for every enemy unit that the assault can see (up to 30%). | *<font color=blue>Aggression</font>: A +10% [[#Critical Hits|crit chance]] bonus for every enemy unit that the assault can see (up to 30%). | ||
*<font color=blue>Close & Personal</font>: Up to a +30% [[#Critical Hits|crit chance]] bonus depending on the distance to the target ''(what distances for what bonuses?)'' | *<font color=blue>Close & Personal</font>: Up to a +30% [[#Critical Hits|crit chance]] bonus depending on the distance to the target ''(what distances for what bonuses?)'' | ||
+ | |} | ||
+ | |||
+ | {| class="wikitable" width="100%" | ||
+ | |- | ||
+ | ! | ||
===[[File: CLASS HEAVY.png|left|24px]]'''[[Heavy (EU2012)|Heavies]]'''=== | ===[[File: CLASS HEAVY.png|left|24px]]'''[[Heavy (EU2012)|Heavies]]'''=== | ||
− | + | |- | |
− | Heavies have very poor aim compared to other classes, but make up for it with a number of abilities which ignore the stat, and at close range their accuracy improves somewhat. Their rockets always have at least a 90% chance to strike their targets, and having them open up on your enemies first can often result in them destroying alien [[Cover_(EU2012)|cover]] or granting other accuracy benefits to their squad-mates (whether the heavies themselves manage to hit or not). | + | |[[Heavy (EU2012)|Heavies]] have very poor aim compared to other classes, but make up for it with a number of abilities which ignore the stat, and at close range their accuracy improves somewhat. Their rockets always have at least a 90% chance to strike their targets, and having them open up on your enemies first can often result in them destroying alien [[Cover_(EU2012)|cover]] or granting other accuracy benefits to their squad-mates (whether the heavies themselves manage to hit or not). |
<center> | <center> | ||
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*<font color=green>Holo-Targeting</font>: +10% aim to all other allied fire on the target until next turn. | *<font color=green>Holo-Targeting</font>: +10% aim to all other allied fire on the target until next turn. | ||
*<font color=grey>Suppression</font>: -30% to the target's aim until next turn or until the heavy is damaged. | *<font color=grey>Suppression</font>: -30% to the target's aim until next turn or until the heavy is damaged. | ||
+ | |} | ||
+ | {| class="wikitable" width="100%" | ||
+ | |- | ||
+ | ! | ||
===[[File: CLASS SNIPER.png|left|24px]]'''[[Sniper (EU2012)|Snipers]]'''=== | ===[[File: CLASS SNIPER.png|left|24px]]'''[[Sniper (EU2012)|Snipers]]'''=== | ||
− | + | |- | |
− | Snipers gain no accuracy bonuses from their high-powered rifles, and in fact take a ''penalty'' if they try to use them at close range (pistols have a better chance to hit at distances less then ten tiles). However, their innate accuracy stats are through the roof, and optional abilities at higher ranks may push them even higher. | + | |[[Sniper (EU2012)|Snipers]] gain no accuracy bonuses from their high-powered rifles, and in fact take a ''penalty'' if they try to use them at close range (pistols have a better chance to hit at distances less then ten tiles). However, their innate accuracy stats are through the roof, and optional abilities at higher ranks may push them even higher. |
<center> | <center> | ||
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*<font color=grey>Low Profile</font>: The sniper receives a high cover bonus of +40% while in low cover, rather then the usual +20%. | *<font color=grey>Low Profile</font>: The sniper receives a high cover bonus of +40% while in low cover, rather then the usual +20%. | ||
*<font color=grey>Headshot</font>: A +30% chance to [[#Critical Hits|crit]]. | *<font color=grey>Headshot</font>: A +30% chance to [[#Critical Hits|crit]]. | ||
+ | |} | ||
+ | {| class="wikitable" width="100%" | ||
+ | |- | ||
+ | ! | ||
===[[File: CLASS SUPPORT.png|left|24px]]'''[[Support (EU2012)|Supports]]'''=== | ===[[File: CLASS SUPPORT.png|left|24px]]'''[[Support (EU2012)|Supports]]'''=== | ||
− | + | |- | |
− | Supports are very "mid-range" in terms of accuracy, and their potential damage output isn't anything to brag about in comparison to other classes. It should be noted that regardless of range, the rifles and pistols available to them will typically each have the same chance to hit as the other (excluding any weapon-specific bonuses, such as that available to the [[Light Plasma Rifle (EU2012)|Light Plasma Rifle]] or [[Foundry_(EU2012)|Foundry]]-upgraded pistols). Their smoke grenades can grant defence bonuses to units they cover. | + | |[[Support (EU2012)|Supports]] are very "mid-range" in terms of accuracy, and their potential damage output isn't anything to brag about in comparison to other classes. It should be noted that regardless of range, the rifles and pistols available to them will typically each have the same chance to hit as the other (excluding any weapon-specific bonuses, such as that available to the [[Light Plasma Rifle (EU2012)|Light Plasma Rifle]] or [[Foundry_(EU2012)|Foundry]]-upgraded pistols). Their smoke grenades can grant defence bonuses to units they cover. |
<center> | <center> | ||
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'''Aim-related abilities:''' | '''Aim-related abilities:''' | ||
*<font color=green>Combat Drugs</font>: A passive bonus granting a +20% aim and +10% [[#Critical Hits|crit chance]] bonus to units firing from within the support's smoke clouds. | *<font color=green>Combat Drugs</font>: A passive bonus granting a +20% aim and +10% [[#Critical Hits|crit chance]] bonus to units firing from within the support's smoke clouds. | ||
− | *<font color=grey>Smoke Grenade</font>: Creates a smoke cloud granting +20% defence to all units (friend or foe) within it. | + | *<font color=grey>Smoke Grenade</font>: Creates a two-turn smoke cloud granting +20% defence to all units (friend or foe) within it. |
*<font color=grey>Rifle Suppression</font>: -30% to target's aim until next turn. | *<font color=grey>Rifle Suppression</font>: -30% to target's aim until next turn. | ||
*<font color=grey>Dense Smoke</font>: A passive bonus causing the support's smoke clouds to grant +40% defence instead of the regular 20%. | *<font color=grey>Dense Smoke</font>: A passive bonus causing the support's smoke clouds to grant +40% defence instead of the regular 20%. | ||
+ | |} | ||
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==Psionic Abilities== | ==Psionic Abilities== | ||
− | + | While [[Psionic_(EU2012)|psionic abilities]] have their own mechanics for determining the odds of success, two are relevant in the discussion of firing accuracy: | |
+ | |||
+ | '''Mind Fray''' is the first ability granted to any budding psionic, and against most races, deals very reliable (if not guaranteed) damage. Assuming it doesn't pop the enemy's head outright, that unit will suffer debuffs for two turns including a -25% aim penalty (better then moving all your units from low to high cover). | ||
+ | |||
+ | '''Telekinetic Field''' is purely defensive; it acts like a dense one-turn smoke cloud, granting +40% defence to any units standing near the point it was triggered. | ||
==Critical Hits== | ==Critical Hits== | ||
''(Stub, will need to link off to [[Damage_(EU2012)|Damage]] for info about, well, damage)'' | ''(Stub, will need to link off to [[Damage_(EU2012)|Damage]] for info about, well, damage)'' | ||
+ | |||
+ | |||
+ | ==The RNG== | ||
+ | Random Number Generators are algorithms intended to produce sets of unpredictable numbers. They are not usually written by regular developers, but rather provided by the programming languages they use. | ||
+ | |||
+ | Computers lack the facilities to "make numbers up". RNGs instead calculate values based on at least two bits of information: a "seed" value, and the number of values that've been returned since that seed was first used (or, if you think of an RNG as a set of dice (with as many sides as you like!), the number of "rolls" you've made with them since starting your game). | ||
+ | |||
+ | Because of this, if you choose a given seed value then ask for five rolls in a row, then reset your roll count to 0 and ask it to perform them again, you'll get the same numbers back every time - so long as you use the same seed. Hence, in order to achieve results that appear truly "random" to the user, the usual technique is to choose a seed value that'd be very hard to predict - like the exact time the program started, in milliseconds - then never intentionally use that seed again. | ||
+ | |||
+ | XCOM (amongst other Firaxis games) deviates from the usual way of doing things by recording the seed and roll count when you save your game. When you fire a shot, a number from about 0 to 99 gets rolled, and if the stated chance to hit was higher, it connects with the target. Because it's not feasible for the player to keep track of the number of rolls made that game - let alone understand the RNG algorithm or determine what the seed might be - the result appears random. | ||
+ | |||
+ | But what if you saved the game before firing, then reload and try it again? The same seed/roll count/algorithm gets used, and so the result generated is the same. | ||
+ | |||
+ | The result is an impression that the game's events are pre-determined, but they're truthfully only calculated when and where they're required. The goal is, of course, to prevent players from cheating - by reloading high-risk shots over and over until the dice roll in their favour and it "connects". | ||
+ | |||
+ | If the system has a flaw, it's that knowing whether the next roll will be high or low makes it easy to decide whether you should have your rookie chance that long-range shotgun shot, or perhaps just have everyone hunker down and let the alien suffer that particular roll of the dice on his turn. | ||
Revision as of 07:54, 28 January 2013
In XCOM: Enemy Unknown, the chance that any given shot will land on your target is based on the sum total of a number of variables. Some work for you, some work against you, but all are additive: if you're told that shiny new rifle gives you a +10 Aim, then indeed your final chance to hit simply goes up by 10% when you're using it. Understanding this game mechanic will help you determine whether a tile is worth moving to, whereas weighing up the chance to hit a target against the amount of damage you might deal to it is useful when considering taking a defensive action instead.
Aim (or Attack) is the base statistic each unit has which accounts for the bulk of its accuracy in battle. For XCOM units, this goes up at a set rate based on rank and class, whereas for aliens it's determined by their race and the difficulty level.
Defence, on the other hand, is the statistic which lowers each unit's chance to be hit. Your units may improve their base defence stat pre-battle by donning certain forms of armour (keeping in mind that most only grant additional hitpoints, lessoning the effects of damage, rather then your chance to avoid it altogether). Some alien races have an innate defensive bonus which is further increased on higher difficulties.
In addition, units may source additional aim/defence bonuses from soldier perks, terrain factors and equipment, cover being one of the most important examples.
The chance to score a Critical Hit is calculated in much the same way, though the percentage displayed is dependant on the shot hitting in the first place. If you're shown an 80% chance to hit with a 25% chance of a critical, then your real chance to score a critical hit on the target is 20% (a 20% chance of missing, a 60% chance to score a regular hit, and a 20% (25% of 80) chance of getting a critical).
Just before OK'ing a shot on your target, you may select "More Info" within the game's HUD to see a list of which modifiers would apply to it.
Solder Stats
A typical XCOM rookie starts off with a flat 65 Aim stat. Generally, as their rank improves, they gain additional points at a static rate (that is to say, a Lieutenant Sniper will always have an Aim stat of 84). Second Wave options can instead be used to mix up the abilities of your ranks - "Not Created Equally" has them start with an aim stat of somewhere from 55 to 80, whereas "Hidden Potential" randomises their gains.
The DLC unit Shaojie Zhang has an extra +5 Aim relative to other non-Second Wave affected heavies. Heroes may also exceed the norm (Ken Levine in particular clocks in with a massive score of 200, nearly double the usual potential of his sniper class!).
In addition to their base stats, each class may choose from a variety of perks which can potentially improve accuracy, decrease it in exchange for another bonus, raise their defence, or affect the aim/defence values of other units in play:
Assaults | ||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
The Assault class sports moderate accuracy, but their shotguns grant huge bonuses at near range - and they're very good at closing the distance. At distances further then ten tiles, their pistols (or perhaps rifles, if equipped) make for more reliable damage, albeit somewhat reduced in power. They can acquire abilities that improve their defence when up in the alien's faces.
Related abilities:
|
Heavies | ||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Heavies have very poor aim compared to other classes, but make up for it with a number of abilities which ignore the stat, and at close range their accuracy improves somewhat. Their rockets always have at least a 90% chance to strike their targets, and having them open up on your enemies first can often result in them destroying alien cover or granting other accuracy benefits to their squad-mates (whether the heavies themselves manage to hit or not).
Related abilities:
|
Snipers | ||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Snipers gain no accuracy bonuses from their high-powered rifles, and in fact take a penalty if they try to use them at close range (pistols have a better chance to hit at distances less then ten tiles). However, their innate accuracy stats are through the roof, and optional abilities at higher ranks may push them even higher.
Related abilities:
|
Supports | ||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Supports are very "mid-range" in terms of accuracy, and their potential damage output isn't anything to brag about in comparison to other classes. It should be noted that regardless of range, the rifles and pistols available to them will typically each have the same chance to hit as the other (excluding any weapon-specific bonuses, such as that available to the Light Plasma Rifle or Foundry-upgraded pistols). Their smoke grenades can grant defence bonuses to units they cover.
Aim-related abilities:
|
Alien Stats
Aliens are, for the most part, about on par with lower-ranked XCOM soldiers, though on difficulty levels above normal they receive a +10 aim/crit bonus (and an extra +10 aim for Outsiders and Muton Elites on Impossible).
Many aliens have innate defensive bonuses, which XCOM solders require certain forms of armour to acquire.
It's worth noting that the Light Plasma Rifle seen earlier on in the game (especially favoured by Thin Men) confers an additional +10 bonus to its wielder (though it's been reported that this doesn't apply to the aliens - so maybe this is only worth noting on the basis that it doesn't work?). Those aliens which use melee attacks (the Chryssalid, the Zombie, and the Muton Berserker) never miss.
Name | Aim | Defence | Name | Aim | Defence |
---|---|---|---|---|---|
Sectoid | 65 | 0 | Outsider | 70 | 0 |
Thin Man | 65 | 0 | Floater | 50 | 0 |
Chryssalid | Melee | 10 | Muton | 70 | 10 |
Zombie | Melee | 0 | Drone | 60 | 10 |
Cyberdisc | 70 | 10 | Sectoid Commander | 85 | 20 |
Muton Berserker | Melee | 20 | Sectopod | 80 | 30 |
Heavy Floater | 70 | 10 | Muton Elite | 80 | 20 |
Ethereal | n/a | 40 | Uber Ethereal | n/a | 40 |
Weapon Range
An aim bonus may be granted based on the distance to the target, depending on the type of weapon used. For the purposes of determining this bonus, guns always fall into one of three different categories: shotguns, sniper rifles, and "everything else".
Most - from the humble Pistol through to the legendary Heavy Plasma - are treated the same in terms of accuracy. Have two soldiers at the same distance from your target, each'll get the same range bonus as the other. Such weapons may only receive range bonuses - if you're too far away to receive one (ten tiles or more), then there's no penalty.
The rifles used by Snipers, on the other hand, are the reverse: being closer to your target inflicts a penalty, and moving further away simply lessons this (again, a distance of ten tiles or more is where range ceases to have any bearing on accuracy).
The only weapon type that has access to a range bonus in addition to a penalty is the shotgun class used by Assaults. A distance of less then ten tiles sees their accuracy spike up at a much faster rate then other weapons; but a distance further then ten tiles inflicts a penalty at the exact same rate (though oddly enough, no such penalty applies to their damage - if they happen to hit at range, they'll be just as devastating as a point-blank blast to the face).
The following formulas describe accuracy drop-off. Again, note that if the standard weapon bonus drops below 0, it's ignored, if the sniper bonus rises above 0 it's ignored, and the shotgun formula always applies. x and y describe the distance in tiles along each axis between the target and the shooter (i.e. Pythagoras is used to get the proper distance on any angle). Final results are rounded down.
Standard Guns | Shotgun Class | Sniper Class |
---|---|---|
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In addition, a very slight fractional penalty may be applied depending on the direction the shot is coming from. For example, a soldier with a rifle sitting an exact two tiles away from an alien may have a 33% range bonus, but another soldier with the same weapon and at the same distance might only get a 32% bonus if he's on a 90° angle (it appears this is because the base bonus drops from 42 to 41.6 in such a case).
A list of pre-calculated values for some ranges have been recorded here.
Note: The partial brackets used in the shotgun formula represent a floor operation, or to put it another way, "round this value down".
Note 2: These formulas may not be 100% accurate.
Equipment
Weapons
Items
Armour
Other Factors
(Stub, will detail potential cover/height bonuses then link off to Cover for info about flanking. Also talk about hunkering down and overwatch (note - what sort of penalties does Covering Fire get?).)
Psionic Abilities
While psionic abilities have their own mechanics for determining the odds of success, two are relevant in the discussion of firing accuracy:
Mind Fray is the first ability granted to any budding psionic, and against most races, deals very reliable (if not guaranteed) damage. Assuming it doesn't pop the enemy's head outright, that unit will suffer debuffs for two turns including a -25% aim penalty (better then moving all your units from low to high cover).
Telekinetic Field is purely defensive; it acts like a dense one-turn smoke cloud, granting +40% defence to any units standing near the point it was triggered.
Critical Hits
(Stub, will need to link off to Damage for info about, well, damage)
The RNG
Random Number Generators are algorithms intended to produce sets of unpredictable numbers. They are not usually written by regular developers, but rather provided by the programming languages they use.
Computers lack the facilities to "make numbers up". RNGs instead calculate values based on at least two bits of information: a "seed" value, and the number of values that've been returned since that seed was first used (or, if you think of an RNG as a set of dice (with as many sides as you like!), the number of "rolls" you've made with them since starting your game).
Because of this, if you choose a given seed value then ask for five rolls in a row, then reset your roll count to 0 and ask it to perform them again, you'll get the same numbers back every time - so long as you use the same seed. Hence, in order to achieve results that appear truly "random" to the user, the usual technique is to choose a seed value that'd be very hard to predict - like the exact time the program started, in milliseconds - then never intentionally use that seed again.
XCOM (amongst other Firaxis games) deviates from the usual way of doing things by recording the seed and roll count when you save your game. When you fire a shot, a number from about 0 to 99 gets rolled, and if the stated chance to hit was higher, it connects with the target. Because it's not feasible for the player to keep track of the number of rolls made that game - let alone understand the RNG algorithm or determine what the seed might be - the result appears random.
But what if you saved the game before firing, then reload and try it again? The same seed/roll count/algorithm gets used, and so the result generated is the same.
The result is an impression that the game's events are pre-determined, but they're truthfully only calculated when and where they're required. The goal is, of course, to prevent players from cheating - by reloading high-risk shots over and over until the dice roll in their favour and it "connects".
If the system has a flaw, it's that knowing whether the next roll will be high or low makes it easy to decide whether you should have your rookie chance that long-range shotgun shot, or perhaps just have everyone hunker down and let the alien suffer that particular roll of the dice on his turn.
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Action System • Movement • Chance to Hit • Cover • Critical Hits • Critical Wounds • Damage • Flanking • Overwatch • Suppression |