Difference between revisions of "Guaranteed damage reduction"

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Wearing heavy body armour provides you with an amount of [[guaranteed damage reduction]] in melee combat. This is a percentage of an enemy's maximum possible damage output that you ignore from each of its hits. Because enemies rarely hit for their max damage, the GDR on some of the heaviest armours often reduces enemy damage to 0, and those hits that do get through are greatly reduced.
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{{version023}}
  
Your GDR% = (14*(Body Armour Base AC-2)^(1/2))% (see chart below for exact figures with each armour). However, the amount of damage you can ignore this way is capped at one half of your total AC. While equipment in other slots, enchantments, and the Armour skill will raise your AC and thus raise the cap, your GDR% is only determined by the body armour you wear. So long as enemy attacks aren't hitting the cap, however, you will see them deal 0 damage per hit GDR% of the time.
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Wearing any body armour with [[AC]] greater than 2 provides you with an amount of '''guaranteed damage reduction (GDR)''' in melee combat. Normally, each attack that hits you is reduced by a random amount up to your AC. GDR is a form of insurance against poor AC rolls; if you have sufficient AC, you are guaranteed to reduce the damage taken by a percentage of the enemy's maximum attack damage equal to your GDR up to half of your AC. As an enemy's damage output is about as variable as your AC, a high GDR will allow you to completely negate an enemy's attacks much more often than normal, and those attacks that do get through will always be significantly diminished.
  
==What It Works Against==
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==Calculating GDR==
GDR works against one thing: physical damage from monsters bashing you in melee (including via a [[reaching]] brand). It does not work against any sort of ranged attack, be it from a physical launcher or a [[Conjurations]] spell that deals physical damage. Neither does it work against melee attacks that are non-physical, such as an [[ice beast]]'s cold damage. However, most such attacks need to do damage to you in the first place to trigger their added effects, so high GDR will make them happen less often.
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In most cases, your GDR% = (14*(Body Armour Base AC-2)^(1/2))%. While other types of armour can provide additional AC, only your body armour can provide GDR. [[Gargoyle]]s instead calculate GDR after adding 5 to the Body Armour Base AC; this results in far greater GDR than usual, especially when wearing light armour (which combos well with their natural AC bonus).
  
==GDR of Various Armours==
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===GDR of Various Armours===
 
{| class="wikitable"
 
{| class="wikitable"
! Armour || Base AC || GDR
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! Armour || Base AC || GDR || Gargoyle GDR
 
|-
 
|-
| [[Robe]], [[animal skin]] || 2 || 0%
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| [[Robe]], [[animal skin]] || 2 || 0% || 31%
 
|-
 
|-
| [[Leather armour]] || 3 || 14%
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| [[Leather armour]] || 3 || 14% || 34%
 
|-
 
|-
| [[Troll leather armour]] || 4 || 19.79%
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| [[Troll leather armour]] || 4 || 19% || 37%
 
|-
 
|-
| [[Ring mail]], [[steam dragon armour]] || 5 || 24.25%
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| [[Ring mail]], [[steam dragon scales]] || 5 || 24% || 39%
 
|-
 
|-
| [[Mottled dragon armour]], [[scale mail]] || 6 || 28%
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| [[Scale mail]], [[acid dragon scales]] || 6 || 28% || 42%
 
|-
 
|-
| [[Chain mail]], [[swamp dragon armour]] || 7 || 31.30%
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| [[Swamp dragon scales]] || 7 || 31% || 44%
 
|-
 
|-
| [[Splint mail]], [[fire dragon armour]] || 8 || 34.29%
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| [[Chain mail]], [[fire dragon scales]] || 8 || 34% || 46%
 
|-
 
|-
| [[Ice dragon armour]] || 9 || 37.04%
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| [[Ice dragon scales]], [[quicksilver dragon scales]] || 9 || 37% || 48%
 
|-
 
|-
| [[Plate mail]], [[pearl dragon armour]], [[storm dragon armour]] || 10 || 39.60%
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| [[Plate armour]], [[pearl dragon scales]], [[storm dragon scales]], [[shadow dragon scales]] || 10 || 39% || 50%
 
|-
 
|-
| [[Gold dragon armour]] || 12 || 44.27%
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| [[Gold dragon scales]] || 12 || 44% || 54%
 
|-
 
|-
| [[Crystal plate armour]] || 14 || 48.50%
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| [[Crystal plate armour]] || 14 || 48% || 58%
 
|-
 
|-
 
|}
 
|}
  
==Strategy==
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There are also three [[transformation]]s which grant GDR despite effectively disabling your body armour: [[Dragon Form]] (34%), [[Statue Form]] (39%), and [[Tree Form]] (48%). Using these forms is the only way that species that cannot wear body armour ([[draconian]]s, [[octopode]]s, and [[felid]]s) can have GDR.
GDR is a very desirable property to have in your armour. It is a major reason for casters to consider wearing leather armour over a robe: 14% is a significant amount of guaranteed damage reduction. On the other hand, the powerful [[robe of the Archmagi|archmagi]] and [[Resistance (ego)|resistance]] brands are only found on robes, so the decision is not always clear-cut.
 
  
For fighter types, GDR is the main reason to go for heavier and heavier armours: If you aren't casting and are planning on training Armour, you should wear the first plate mail you find: the GDR is well worth the accuracy penalties. Later on, you might want to upgrade to a crystal plate mail or a gold dragon armour, though a branded, enchanted plate mail is a worthy ascension kit item as well.
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==What GDR Affects==
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GDR only works against one thing: physical damage dealt by monsters attacking you in melee (including via [[reaching]]). It does not work against any sort of ranged attack, be it from a physical launcher or a [[Conjurations]] spell that deals physical damage. Neither does it work against elemental melee damage, such as an [[ice beast]]'s additional cold damage; however, most such elemental attacks need to deal physical damage to you before their added effects trigger, so high GDR will make them happen less often.
  
==Example==  
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==Guaranteed Damage Reduction Cap==
30 AC with a +6 chain mail is worse than 28 AC with a +0 plate mail.  
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GDR is '''not''' a form of damage reduction independent from AC. If you have excellent GDR and terrible AC, it will do you little good. The damage reduction is capped at your GDR% of the enemy's maximum damage or 1/2 of your AC, whichever is lower.
  
The graph below lists the average damage taken after GDR calculations for a 28 AC plate vs a 30 AC chain. The plate has 40% damage reduction while the chain has 28% damage reduction. Note this omits the AC damage reduction check that can be greater than the GDR value.
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For example, let's say you have 48% GDR and 100 AC, and you're facing an opponent capable of dealing up to 50 damage in a single hit. This would give you a guaranteed damage reduction of 24 (48% of 50), taking full advantage of the 48% GDR. The same 48% GDR coupled with 20 AC would only give a guaranteed reduction of 10, a mere 20% of the enemy's max damage, because it is capped at 1/2 of your AC. If you are instead facing an opponent capable of dealing 200 damage, then even at 100 AC, you'd only be guaranteed 50 damage reduction (25%), while the 20 AC character would still be stuck with 10 (which is now only 5%). In each of these cases, the GDR is still helping; even in the case of 20 AC vs. 200 max damage, it still mitigates the worst possible rolls.
  
[[File:GDR_Example.png]]
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Guaranteed damage reduction is effectively a minimum AC roll. If your damage reduction is 24 (as in the first example above) and you roll a 1 on your AC against a given attack, your roll will be boosted up to 24 instead. But if you roll a 36 on your AC, you won't get any bonus from GDR because you're already above the minimum.
  
This chart illustrates an important aspect of GDR: GDR will help reduce damage from small and numerous attacks. With monsters that have a low max damage, you will take less damage with the higher GDR plate mail. For example, for a monster that has a max damage of 15, you will take on average 4.2 damage with the chain mail and 3.0 damage with the plate mail. So while you have a higher AC with the chain mail, you will be taking ''40% more'' damage, on average, than if you wore the plate mail.
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==Strategy==
 
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GDR's usefulness depends heavily on how often you find yourself in melee combat, how high your AC is, and how much you're willing to sacrifice your [[ev]]asion defense (in general, the worse an armour is for your evasion, the higher its GDR will be). Unless you intend to wade into close combat whenever possible ''and'' you have no intention of training [[Dodging]], you'll likely be better off avoiding super-heavy armour while focusing on optimizing your AC, EV, spells, and resistances to keep yourself alive. Characters that actively avoid melee, whether it be through fast movement speed or ranged attacks, will barely notice the effect of their GDR.
The higher AC only starts to overcome the better GDR when the max damage surpasses 50, but by then the difference in reduction is negligible.
 
 
 
==Spell-Based GDR==
 
There are two [[Transmutations]] spells which allow you to have GDR in spite of the fact that they effectively disable your body armour: [[Dragon Form]] (34%) and [[Statue Form]] (39%).
 
  
 
[[Category:Defence]][[Category:Game mechanics]]
 
[[Category:Defence]][[Category:Game mechanics]]

Revision as of 19:45, 21 July 2020

Version 0.23: This article may not be up to date for the latest stable release of Crawl.

Wearing any body armour with AC greater than 2 provides you with an amount of guaranteed damage reduction (GDR) in melee combat. Normally, each attack that hits you is reduced by a random amount up to your AC. GDR is a form of insurance against poor AC rolls; if you have sufficient AC, you are guaranteed to reduce the damage taken by a percentage of the enemy's maximum attack damage equal to your GDR up to half of your AC. As an enemy's damage output is about as variable as your AC, a high GDR will allow you to completely negate an enemy's attacks much more often than normal, and those attacks that do get through will always be significantly diminished.

Calculating GDR

In most cases, your GDR% = (14*(Body Armour Base AC-2)^(1/2))%. While other types of armour can provide additional AC, only your body armour can provide GDR. Gargoyles instead calculate GDR after adding 5 to the Body Armour Base AC; this results in far greater GDR than usual, especially when wearing light armour (which combos well with their natural AC bonus).

GDR of Various Armours

Armour Base AC GDR Gargoyle GDR
Robe, animal skin 2 0% 31%
Leather armour 3 14% 34%
Troll leather armour 4 19% 37%
Ring mail, steam dragon scales 5 24% 39%
Scale mail, acid dragon scales 6 28% 42%
Swamp dragon scales 7 31% 44%
Chain mail, fire dragon scales 8 34% 46%
Ice dragon scales, quicksilver dragon scales 9 37% 48%
Plate armour, pearl dragon scales, storm dragon scales, shadow dragon scales 10 39% 50%
Gold dragon scales 12 44% 54%
Crystal plate armour 14 48% 58%

There are also three transformations which grant GDR despite effectively disabling your body armour: Dragon Form (34%), Statue Form (39%), and Tree Form (48%). Using these forms is the only way that species that cannot wear body armour (draconians, octopodes, and felids) can have GDR.

What GDR Affects

GDR only works against one thing: physical damage dealt by monsters attacking you in melee (including via reaching). It does not work against any sort of ranged attack, be it from a physical launcher or a Conjurations spell that deals physical damage. Neither does it work against elemental melee damage, such as an ice beast's additional cold damage; however, most such elemental attacks need to deal physical damage to you before their added effects trigger, so high GDR will make them happen less often.

Guaranteed Damage Reduction Cap

GDR is not a form of damage reduction independent from AC. If you have excellent GDR and terrible AC, it will do you little good. The damage reduction is capped at your GDR% of the enemy's maximum damage or 1/2 of your AC, whichever is lower.

For example, let's say you have 48% GDR and 100 AC, and you're facing an opponent capable of dealing up to 50 damage in a single hit. This would give you a guaranteed damage reduction of 24 (48% of 50), taking full advantage of the 48% GDR. The same 48% GDR coupled with 20 AC would only give a guaranteed reduction of 10, a mere 20% of the enemy's max damage, because it is capped at 1/2 of your AC. If you are instead facing an opponent capable of dealing 200 damage, then even at 100 AC, you'd only be guaranteed 50 damage reduction (25%), while the 20 AC character would still be stuck with 10 (which is now only 5%). In each of these cases, the GDR is still helping; even in the case of 20 AC vs. 200 max damage, it still mitigates the worst possible rolls.

Guaranteed damage reduction is effectively a minimum AC roll. If your damage reduction is 24 (as in the first example above) and you roll a 1 on your AC against a given attack, your roll will be boosted up to 24 instead. But if you roll a 36 on your AC, you won't get any bonus from GDR because you're already above the minimum.

Strategy

GDR's usefulness depends heavily on how often you find yourself in melee combat, how high your AC is, and how much you're willing to sacrifice your evasion defense (in general, the worse an armour is for your evasion, the higher its GDR will be). Unless you intend to wade into close combat whenever possible and you have no intention of training Dodging, you'll likely be better off avoiding super-heavy armour while focusing on optimizing your AC, EV, spells, and resistances to keep yourself alive. Characters that actively avoid melee, whether it be through fast movement speed or ranged attacks, will barely notice the effect of their GDR.