Difference between revisions of "Guaranteed damage reduction"

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'''Guaranteed damage reduction (GDR)''' gives players a layer of protection 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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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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Your GDR is calculated by the following formula: <code>GDR% = AC^(1/4) * 16</code>. Any means of obtaining AC counts towards your GDR.
  
 
===GDR of Various AC Values===
 
===GDR of Various AC Values===
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! Base AC || GDR
 
! Base AC || GDR
 
|-
 
|-
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| 2 ([[Robe]]) || 1%
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| 2 ([[Robe]]) || 19.0%
 
|-
 
|-
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| 6 ([[Scale mail]]) || 25%
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| 6 ([[Scale mail]]) || 25.0%
 
|-
 
|-
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| 10 ([[Plate armour]]) || 28%
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| 10 ([[Plate armour]]) || 28.5%
 
|-
 
|-
 
| 16 (+2 [[Robe]], aux) || 32%
 
| 16 (+2 [[Robe]], aux) || 32%
 
|-
 
|-
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| 32 (+10 [[Plate armour]], aux) || 38%
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| 32 (+10 [[Plate armour]], aux) || 38.1%
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|-
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| 40 (+14 [[Crystal plate armour|Crystal plate]], aux) ||40.2%
 
|-
 
|-
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| 40 (+14 [[Crystal plate armour| Crystal plate]], aux) ||40%
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| 50 || 42.5%
 
|-
 
|-
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| 50 || 43%
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| 100 || 50.6%
 
|-
 
|-
 
|}
 
|}
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Auxiliary slots include a +2 [[Helmet]], +2 [[Cloak]], +2 [[Gloves]], and some +2 [[Boots]].
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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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==What GDR Affects==
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==Damage Reduction==
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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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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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==Guaranteed Damage Reduction Cap==
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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 is '''not''' a form of damage reduction independent from AC. If you could 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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Guaranteed damage reduction is effectively a minimum AC roll. If your GDR reduces 24 damage (lets say, 48% GDR of a 50 damage hit), 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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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==
 
==Strategy==
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GDR is as useful as [[AC]]; any form of AC will 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. For most characters, GDR will slightly reduce the maximum damage enemies can deal.
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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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For most characters, GDR will slightly reduce the maximum physical damage enemies can deal.
  
 
==History==
 
==History==
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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 a set GDR. [[Gargoyle]]s increased base GDR, while [[Draconian]]s, notably, 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 [[0.27]], 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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