Difference between revisions of "Guaranteed damage reduction"

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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.
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'''Guaranteed damage reduction (GDR)''' gives players a layer of protection in melee and ranged combat. Normally, each attack that hits you is reduced by a random amount up to your AC. Against physical attacks, your minimum AC reduction is equal to GDR% of the attack's damage, unless this would be higher than <code>1/2 * AC</code>. Therefore, GDR is a form of insurance against poor AC rolls.
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==What GDR Affects==
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GDR only works against physical damage, either in melee, with [[reaching]], or with a ranged/throwing weapon.
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It does ''not'' apply against any sort of spell or ability. Therefore, GDR does not apply to a [[Conjurations]] spell that does physical damage. Neither does it apply against "physical" abilities like [[Slug Dart]] or [[Harpoon Shot]]. It also doesn't work against elemental melee damage, such as an [[ice beast]]'s additional cold damage.
  
 
==Calculating GDR==
 
==Calculating GDR==
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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).
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Your GDR is calculated by the following formula: <code>GDR% = AC^(1/4) * 16</code>. Any means of obtaining AC counts towards your GDR.
  
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===GDR of Various Armours===
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===GDR of Various AC Values===
 
{| class="wikitable"
 
{| class="wikitable"
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! Armour || Base AC || GDR || Gargoyle GDR
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! Base AC || GDR
 
|-
 
|-
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| [[Robe]], [[animal skin]] || 2 || 0% || 31%
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| 2 ([[Robe]]) || 19.0%
 
|-
 
|-
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| [[Leather armour]] || 3 || 14% || 34%
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| 6 ([[Scale mail]]) || 25.0%
 
|-
 
|-
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| [[Troll leather armour]] || 4 || 19% || 37%
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| 10 ([[Plate armour]]) || 28.5%
 
|-
 
|-
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| [[Ring mail]], [[steam dragon scales]] || 5 || 24% || 39%
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| 16 (+2 [[Robe]], aux) || 32%
 
|-
 
|-
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| [[Scale mail]], [[acid dragon scales]]  || 6 || 28% || 42%
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| 32 (+10 [[Plate armour]], aux) || 38.1%
 
|-
 
|-
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| [[Swamp dragon scales]] || 7 || 31% || 44%
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| 40 (+14 [[Crystal plate armour|Crystal plate]], aux) ||40.2%
 
|-
 
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| [[Chain mail]], [[fire dragon scales]] || 8 || 34% || 46%
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| 50 || 42.5%
 
|-
 
|-
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| [[Ice dragon scales]], [[quicksilver dragon scales]] || 9 || 37% || 48%
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| 100 || 50.6%
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|-
 
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| [[Plate armour]], [[pearl dragon scales]], [[storm dragon scales]], [[shadow dragon scales]] || 10 || 39% || 50%
 
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|-
 
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| [[Gold dragon scales]] || 12 || 44% || 54%
 
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|-
 
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| [[Crystal plate armour]] || 14 || 48% || 58%
 
 
|-
 
|-
 
|}
 
|}
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Auxiliary slots include a +2 [[Helmet]], +2 [[Cloak]], +2 [[Gloves]], and +2 [[Boots]]. Percents on this table are rounded to the nearest tenth.
  
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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.
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==Damage Reduction==
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GDR is '''not''' a form of damage reduction independent from AC. If you could have excellent GDR and terrible AC, it would do you little good. It is effectively a minimum AC roll, or a ''guaranteed'' AC roll. It is capped at <code>GDR% * damage taken</code> or <code>1/2 * AC</code>, whichever is lower.
  
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==What GDR Affects==
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Let's say you take a 50 damage attack, but have 48% GDR. First, [[AC]] rolls. If AC roll is a 1, then GDR will raise the reduction to (50 * .48) = 24, meaning you actually lose 26 HP. But if your AC roll is 36, then GDR will not do anything, as you are above the guaranteed reduction of 24.  
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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.
 
  
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==Guaranteed Damage Reduction Cap==
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If you took said 50 damage attack with 16 AC and 32% GDR, then the AC/2 limit applies instead: you'll always reduce damage by at least (16 / 2) = 8 over the expected (50 * .32) = 16.
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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.
 
  
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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.
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==Strategy==
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GDR is tied to your [[AC]]; any form of extra AC will also increase GDR. This comes with the same costs and benefits; are you willing to sacrifice [[EV]] and spellcasting potential in order to become more bulky? Characters who want to avoid melee will still want to avoid melee as much as possible. However, GDR is a large reason why AC is more consistent in stopping damage.
  
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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.
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For most characters, GDR will slightly reduce the maximum physical damage enemies can deal.
  
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==Strategy==
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==History==
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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.
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*Prior to [[0.27]], GDR was more complex. Each set of body [[armour]] had a defined GDR, calculated by <code>(14 * (Body Armour Base AC - 2)^(1/2))%</code>, no matter what your actual AC was. Certain [[transmutation]]s also had a set GDR. [[Gargoyle]]s increased base GDR, while [[Draconian]]s (being unable to wear body armour) didn't have any. For more information, see [http://crawl.chaosforge.org/index.php?title=Guaranteed_damage_reduction&oldid=52698 this past revision].
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*Prior to [[0.8]], GDR was equal to <code>(Body Armour Base AC) * (13 + Armour) / 17</code>.
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*Prior to [[0.5]], GDR was higher.
  
 
[[Category:Defence]][[Category:Game mechanics]]
 
[[Category:Defence]][[Category:Game mechanics]]

Latest revision as of 05:02, 17 December 2023

Version 0.30: This article may not be up to date for the latest stable release of Crawl.

Guaranteed damage reduction (GDR) gives players a layer of protection in melee and ranged combat. Normally, each attack that hits you is reduced by a random amount up to your AC. Against physical attacks, your minimum AC reduction is equal to GDR% of the attack's damage, unless this would be higher than 1/2 * AC. Therefore, GDR is a form of insurance against poor AC rolls.

What GDR Affects

GDR only works against physical damage, either in melee, with reaching, or with a ranged/throwing weapon.

It does not apply against any sort of spell or ability. Therefore, GDR does not apply to a Conjurations spell that does physical damage. Neither does it apply against "physical" abilities like Slug Dart or Harpoon Shot. It also doesn't work against elemental melee damage, such as an ice beast's additional cold damage.

Calculating GDR

Your GDR is calculated by the following formula: GDR% = AC^(1/4) * 16. Any means of obtaining AC counts towards your GDR.

GDR of Various AC Values

Base AC GDR
2 (Robe) 19.0%
6 (Scale mail) 25.0%
10 (Plate armour) 28.5%
16 (+2 Robe, aux) 32%
32 (+10 Plate armour, aux) 38.1%
40 (+14 Crystal plate, aux) 40.2%
50 42.5%
100 50.6%

Auxiliary slots include a +2 Helmet, +2 Cloak, +2 Gloves, and +2 Boots. Percents on this table are rounded to the nearest tenth.

Damage Reduction

GDR is not a form of damage reduction independent from AC. If you could have excellent GDR and terrible AC, it would do you little good. It is effectively a minimum AC roll, or a guaranteed AC roll. It is capped at GDR% * damage taken or 1/2 * AC, whichever is lower.

Let's say you take a 50 damage attack, but have 48% GDR. First, AC rolls. If AC roll is a 1, then GDR will raise the reduction to (50 * .48) = 24, meaning you actually lose 26 HP. But if your AC roll is 36, then GDR will not do anything, as you are above the guaranteed reduction of 24.

If you took said 50 damage attack with 16 AC and 32% GDR, then the AC/2 limit applies instead: you'll always reduce damage by at least (16 / 2) = 8 over the expected (50 * .32) = 16.

Strategy

GDR is tied to your AC; any form of extra AC will also increase GDR. This comes with the same costs and benefits; are you willing to sacrifice EV and spellcasting potential in order to become more bulky? Characters who want to avoid melee will still want to avoid melee as much as possible. However, GDR is a large reason why AC is more consistent in stopping damage.

For most characters, GDR will slightly reduce the maximum physical damage enemies can deal.

History

  • Prior to 0.27, GDR was more complex. Each set of body armour had a defined GDR, calculated by (14 * (Body Armour Base AC - 2)^(1/2))%, no matter what your actual AC was. Certain transmutations also had a set GDR. Gargoyles increased base GDR, while Draconians (being unable to wear body armour) didn't have any. For more information, see this past revision.
  • Prior to 0.8, GDR was equal to (Body Armour Base AC) * (13 + Armour) / 17.
  • Prior to 0.5, GDR was higher.
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