Difference between revisions of "Shields"

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(Rewrite with much more information. Maybe too much. More work needed.)
(Undo revision 60236 by Wwf (talk))
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{{Version028}}
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{{version028}}
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{{flavour|“Let who will boast their courage in the field,<br>
 +
I find but little safety from my shield.<br>
 +
Nature's, not honour's, law we must obey:<br>
 +
This made me cast my useless shield away,<br>
 +
And by a prudent flight and cunning save<br>
 +
A life, which valour could not, from the grave.<br>
 +
A better buckler I can soon regain;<br>
 +
But who can get another life again?”<br>
 +
-Archilochos. 7th cent. B.C. trans. William H. Goodwin, 1878.}}
  
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''See [[Weapon Speed]] for tables summarising this information.''
+
[[Shields]] are a kind of armour worn on one hand, preventing the use of two-handed weapons; they make use of the [[Shields skill]]. Unlike other armour, shields increase a character's [[SH]] defense, giving you a chance at blocking physical (and some magical) attacks entirely. There are four types of shield, in order of size:
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''This page goes into great detail about attack delay calculations.''
 
  
−
When deciding between two different weapons, it can be helpful to understand exactly how attack speed works. Each physical attack in ''Crawl'' takes a certain amount of time. A character with a smaller attack delay will swing more frequently than a character with a larger attack delay. This can greatly multiply how often you can inflict damage in combat. So it is strongly recommended to get your attack delay as low as possible.
+
*[[Orb]], which do not actually provide shielding
 +
*[[Buckler]]
 +
*[[Kite shield]]
 +
*[[Tower shield]]
  
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==Attack Delay Calculations for Weapons and Missles==
+
Some magical effects can also increase your SH score.
−
*Note that [[strength]], [[dexterity]] and [[armour]] have no effect on attack delay.
 
−
===Base attack delay===
 
−
All weapons, thrown objects, and launched objects have a base attack delay. You can find this information in game by examining the weapon or launcher. The base attack delay in game should be multiplied by 10 to give the delay in [[aut]]s. The [[Weapon Speed]] page has a complete tables and includes thrown objects. It also lists the base delay in [[aut]]s. For reference most species move and cast spells with a delay of 10 [[aut]]s.
 
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===Minimum attack delay===
 
−
By raising your skill with the weapon or launcher you can reduce attack delays to the minimum attack delay. The minimum delay is usually 1/2 the base delay rounded down. If this is greater than 7 then the minimum attack delay is set to 7. There are three exceptions to this rule:
 
−
*[[Short blades]]: The rapier with a base delay of 12 has a minimum delay of 5.
 
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*All [[Crossbows]] have a minimum delay of 10.
 
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*The [[Woodcutter's axe]] always has a delay of 10 irregardless of skills.
 
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===Skill adjustments===
 
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Weapon, launcher, or throwing skills brings down the attack delay by <code>(skill level)/2</code> until you reach minimum weapon delay. Increasing your skill beyond that will not let you attack faster but it will slightly improve your damage and accuracy with the weapon. Normally you turn off your weapon skill when you hit minimum delay and dump experience points into increasing skills in other areas. The gods [[Ashenzari]] and [[Okawaru]] can increase your weapon skills and thus contribute to lowering your weapon delay.
 
−
===Speed Brand===
 
−
The [[speed (brand)|speed brand]] further reduces the delay to 2/3 of the skill adjusted delay.
 
−
With skill and speed brand improvements there is a hard coded minimum delay of 3.
 
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===Shield Penalties===
 
−
[[Shields]] will slow down weapon speed. This slow down can be reduced by increasing your [[shields (skill)|shield skill]].
 
−
The detailed formula is <code>2*(shield encumberance)^2*(270-(10x shield skill))*scale/(5*(20-3*(size factor))/270</code>.
 
−
The values for shield encumberance and size factor can be found on the [[shields]] page. The scale used in this formula is 20. The game does display the [[Encumbrance rating|shield encumberance]] when describing the item, but it does not report the character size factor. Notice the shield penalty can be reduced to zero with a shield skill of 27.
 
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===God Given Abilities===
 
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The god [[Okawaru]]'s Finesse ability will further cut the delay in half. Note that this will not stack with haste nor berserk.
 
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===Status modifiers===
 
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*[[Potion of haste|Haste]] and [[berserk]] will further reduce the delay to 2/3 of its calculated value if you have not invoked Finesse. You cannot be both hasted and berserked.
 
−
*[[Statue Form]], [[Petrify]]ing, and [[Slow]]ness will increase the delay to 3/2 of the calculated value. These status conditions do stack with haste resulting in a net cancellation of the two different statuses. Slowness can stack with both statue form and petrifying.
 
−
*In no case, will the delay be reduced below 2.
 
  
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==Unarmed Combat==
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==Shield Penalties==
−
[[Unarmed combat]] has a different attack delay calculation. It is <code>10-(unarmed combat skill)/54</code>. You start with a delay of 10 with no unarmed combat skill and reach a minimum delay of 5 with an unarmed combat skill of 27. The shield penaties, god given abilities and status modifiers apply to unarmed combat as well.
+
Wearing a shield also gives penalties to attack speed, EV, and spellcasting. While the penalty for wearing a small buckler is almost negligible, a tower shield can seriously slow your attacks and make spellcasting unreliable.  
  
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==Spells==
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Specifically, your shield penalty is <code>2/5 * encumbrance^2 / (20 - 3 * size_factor) * (27 - shield_skill) / 27</code><ref>{{source ref|0.28.0|player.cc|5587}}</ref>. This is your penalty to your evasion, which gets used to calculate everything else. This means that larger species can wield shields more comfortably, while anyone can eliminate shield penalty by maxing out the Shields skill.
−
Spells can be used for attacking and thus are included on this page. The base delay for casting a spell is 10. It can be modified by status modifiers but delay is not affected by skill, shields, or god abilities.
 
−
An exception to this is the spell [[Manifold Assault]]. The delay of casting manifold assault is the calculated weapon or unarmed combat delay.
 
  
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==Movement Based Attacks==
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{| class="prettytable" cellpadding="10" border="9"
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Some attacks are combined with movement. Even if the actual attack delay is not changed, they are mentioned here for completeness.
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|- align="center"
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===Martial Arts Attacks===
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! Shield type !! Encumbrance
−
The [[Wu Jian]] Council allows a player to make a number of different martial arts attacks. The number of attacks is based on the attack delay and the movement delay. The movement delay is:
+
|-
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*10 if you have invoked the serpent's lash ability, or
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|Buckler || 5
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*twice your movement delay if you have invoked the wall jump ability. (The wall jump ability takes two turns.)
+
|-
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*Otherwise your normal movement delay is used.
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|Kite shield || 10
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Your attack delay is the delay calculated in the previous sections. The number of attacks is the movement delay divided by the attack delay. If this is not an integer, the number of attacks could be rounded up or down. The number of attacks will average out to the non-integer number of attacks calculated. Extreme examples of the numbers of attacks would be a spriggan wielding a triple cross bow. With a movement delay of 6 and an attack delay of 23 the spriggan would only make one attack 6/23 of the time. The other extreme would be a naga wielding a quick blade with sufficient short blade skill. The naga's movement delay would be 14 and the weapon delay would be 3. For a wall jump which counts as two turns the expected number of attacks would be 28/3. So there could be 10 attacks 1/3 of the time.
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|-
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*Note that the serpent's lash ability allows you to take two turns to make martial arts attacks without taking any time.
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|Tower shield || 15
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===Charging Attacks===
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|}
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*The [[rampaging]] ego allows you to move towards a target and attack. The time taken is the attack delay and not the movement delay. Even a naga wielding a quick blade with sufficient [[short blade]] skill can move and attack a target with a delay of 3. Compare this with a naga's movement delay of 14.
+
 
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*A [[palentonga]]'s rolling charge allows you to move towards a target and attack. The time taken is the maximum of a movement delay or an attack delay.
+
{| class="prettytable" cellpadding="10" border="9"
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===Bolt Attacks===
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|- align="center"
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There are attacks that can hit multiple targets as you move through them like a bolt.
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! Size !! Races !! Size factor
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*[[Storm Form]] has the blink bolt ability to move through many targets at once doing damage to each.
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|-
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*[[Uskayaw]]'s line pass ability has the same properties.
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|Little || [[Spriggan]] || +4
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===Instintaneous attacks===
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|-
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Some spells and abilities let you appear somewhere else and immediately make an attack without any delay.
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|Small || [[Kobold]] || +2
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*[[Passwall]] takes time to set up on one side of a rock wall. But you appear on the other side and can attack without targets being able to react to you first. This is different than blink which moves you to a new location and then you stay there for the turn delay.
+
|-
 +
|Normal || most races || 0
 +
|-
 +
|Normal<br>(strong arms)||[[Formicid]] || -2
 +
|-
 +
|Large<br>(normal torso)|| [[Palentonga]], [[Naga]]|| -2
 +
|-
 +
|Large || [[Ogre]], [[Troll]] || -2
 +
|}
 +
 
 +
When attacking with any kind of weapon (including unarmed), if you are wearing a shield and your Shield penalty is greater than zero, the game throws two dice with (Shield penalty) sides. The smaller value rolled is added to your attack delay.
 +
 
 +
==[[Ego]]s==
 +
All three types of shields can spawn with the following egos<ref>{{source ref|0.28.0|makeitem.cc|768}}</ref>:
 +
*~3%, [[Resistance_(ego)|resistance]]
 +
*10%, [[fire resistance]]
 +
*10%, [[cold resistance]]
 +
*10%, [[poison resistance]]
 +
*10%, [[positive energy]]
 +
*19%, [[reflection]]
 +
*39%, [[protection]]
  
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==Detailed Calculations==
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Shields of [[cold resistance|cold]] and [[fire resistance]] can occasionally be found in [[ice cave]]s and [[volcano]]es.
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The formulas above give you a very close approximation to the average attack delay. Most players can use the values above or the values on the [[weapon speed]] page without needing to know about the detailed calculations in this section.
 
−
===Averaging Fractional Delays===
 
−
Most calculations above can result in fractional delays. If you have a [[short sword]] with a base delay of 11 and a [[short blades|short blade skill]] of 5.7, the formula above would give you an average delay of <code>11-5.7/2 = 8.15</code>. The game mechanics give you an average delay by rolling a delay of 8 85% of the time and a delay of 9 15% of the time. This is needed because all delays are integer values of [[aut]]s.
 
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===Using Statistical Random Variables===
 
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The fractional delays do not give the entire story because each stage attack delay calculations involve creation of a new random variable. These random variables actually contain all possible integer delays and their weighted probabilities. This can result in a much wider range of attack delays than the averaging of fractional delays would imply. To complicate things, all calculations are done with a fixed precision.
 
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This is best explained by examples.
 
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====Example 1====
 
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Let's use the example of a [[human]] wielding a short sword and a buckler. The human has a [[short blade|short blade skill]] of 7.5 and a shield skill of 4. The [[buckler]]'s encumberance is 5. The human size factor is zero and can be found on the [[shields]] page. There are three random variabls used.
 
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*The first is the base delay of the short sword of 11 [[aut]]
 
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*The second random variable encorporates the additional skill adjustment delay of -skill*10/scale = -75/20
 
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*The third random variable encorporates the additional shield penalty delay of 8/20
 
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*The final probabilities: delay=7 47.4%, delay=8 47.4%, delay=9 5.3%
 
  
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{| class="wikitable"
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==Blocking==
 +
===Effect===
 +
It's possible to block a melee attack or a ranged projectile attack if you wear a shield of some kind or are under the effect of a magical shield ([[amulet of reflection]], [[Qazlal]]'s Storm Shield, or [[the Shining One]]'s Divine Shield) or have the [[Good_mutations#Large_Bone_Plates|Large Bone Plates]] mutation. Your ability to block missiles doesn't benefit from [[Repel Missiles|missile-repelling]] effects like a [[scarf]] of repulsion, and you cannot benefit from any form of shield while you are [[confuse]]d.
 +
 
 +
All melee attacks can be blocked (except for successful [[stab]]s), but many ranged attacks are unblockable:
 +
*[[Penetration|Penetrating]] attacks: [[Javelin]]s, [[Bolt spell]]s, [[Starburst]]...
 +
*Explosions: [[Fireball]], [[Damnation]], [[Conjure Ball Lightning]]...
 +
*Electrical discharges: [[Static Discharge]], [[Chain Lightning]]
 +
*Enchantments: [[Agony]], [[Pain]], [[Confuse]], [[Mesmerise]]...
 +
*Beams with perfect accuracy: [[Magic Dart]], [[Freeze]], [[Smite]]...
 +
*Other ranged attacks that are not beams: [[Shatter]], [[Polar Vortex]], [[Ozocubu's Refrigeration]]
 +
 
 +
Some examples of ranged attacks that can be blocked:
 +
*Ranged weapons like [[Bows]] or [[Slings]]
 +
*Spells that fire projectiles like [[Iron shot]], [[Poison Arrow]], [[Orb of Destruction]], [[Sandblast]]
 +
 
 +
If the attacker's pierce value is less than the defender's blocking value (see below for details), the attack does no damage. Shield blocking is done before rolling your [[evasion]] or your [[AC]], but if you have already blocked some attacks in that turn, your blocking ability will be decreased greatly.
 +
 
 +
===Calculation===
 +
The defender's blocking value depends on the nature of the shield:
 +
 
 +
Physical shields:
 +
SH = Block × (1 + Shield skill/40)
 +
+ Enchantment bonus + Stat bonus
 +
+ min(0.38×Shield skill, .57 + 0.19×Shield skill)
 +
 
 +
and then on top of either of those:
 +
+ Divine shield bonus
 +
+ Qazlal shield bonus
 +
+ Mutation bonus
 +
+ Amulet of reflection bonus
 +
+ Any SH bonus from artifacts
 +
 
 +
For a physical shield (Buckler, Kite Shield, and Tower Shield), '''Block''' is the shield's blocking value, equal to the base shield bonus (3 for Buckler, 8 for Kite Shield, 13 for Tower Shield), modified by a size factor:
 +
 
 +
{| class="prettytable" cellpadding="10" border="9"
 
|- align="center"
 
|- align="center"
−
!
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! Size !! Races !! Buckler !! Kite Shield !! Tower shield
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!colspan="8"|Delays|
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|-
 +
|Little || [[Spriggan]] || +2 || - || -
 
|-
 
|-
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! Explaination !! 6 !! 7 !! 8 !! 9 !! 10 !! 11 !! 12 !! 13 !! Total Weight
+
|Small || [[Kobold]] || +1 || +0.5 || -
 
|-
 
|-
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|Base delay<br>short sword
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|Normal || most races || 0 || 0 || 0
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|   ||   ||   ||   ||  || 1  ||  || || 1
 
 
|-
 
|-
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|Subtract Skill reduction<br>7.5*scale/20
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|Normal<br>(strong arms)|| [[Formicid]] || 0 || 0 || 0
−
|   || 15  || 5  ||   ||  ||    ||  ||  || 20
 
 
|-
 
|-
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|Add shield penalty<br>
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|Large<br>(normal torso)|| [[Palentonga]], [[Naga]] || 0 || 0 || 0
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2*(5)^2*(270-(10*4))*20<br>/(5*(20-3*(0))/270
 
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<br>=2300/270=8
 
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|   || 15*12  || 15*8 + 5*12  || 5*8  ||  ||    ||  ||  ||  
 
 
|-
 
|-
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|Shield Penalty Weights
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|Large
−
|   || 180 || 180  || 20  ||  ||    ||  ||  || 380
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|| [[Ogre]], [[Troll]] || - || -0.5 || 0
 
|}
 
|}
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*Note that there are three possible delays, not just two based upon one average
+
 
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*A scale is used to create weights which avoids large integer division truncation inaccuracies
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*'''Stat bonus''' is <code> DEX * 38 * (base_shield + 13) / 26 </code>,
−
*A random number from 0-380 is created and a delay is selected based upon which bin the number would fall into.
+
 
 +
*The Shining One's '''Divine shield bonus''' is based on Invocations skill.
 +
 
 +
*'''Mutation bonus''' is +4/6/8 SH depending on your level of the [[Good_mutations#Large_Bone_Plates|Large Bones Plates]] mutation.
 +
 
 +
The resulting value is rounded to the nearest integer and displayed as the player's SH value.
 +
 
 +
The attacker's pierce value is equal to:
 +
 
 +
1d(15 + to hit/2 + 5×past_blocks^2) - 1 (melee attacks)
 +
 
 +
1d(1.3×to hit    + 5×past_blocks^2) - 1 (ranged attacks) 
 +
 
 +
"To hit" is the monster's [[To hit]] value (based primarily on the monster's [[HD]], type, and weapon accuracy) and "past_blocks" is the number of attacks already successfully blocked in the current turn.
 +
 
 +
The defender's blocking value is equal to:
 +
2d(2×SH)/6 - 1.3 (Divided by 3 against melee attacks from invisible opponents)
 +
 
 +
If this value is greater or equal than the attacker's pierce value, the attack is blocked.
 +
 
 +
==History==
 +
*Prior to [[0.28]], the two larger shields used [[Strength]] and [[Dexterity]] to determine SH, and shields had a to-hit penalty. The penalty formula changed; before, certain skill thresholds (4 skill for buckler, 15 for kite shield, 25 for tower shield) negated it.
 +
*In [[0.27]], the shield penalty was increased.
 +
*Prior to [[0.25]], [[kite shield]]s were known as just "shields" and [[tower shield]]s were called "large shields".
 +
*Prior to [[0.17]], [[unarmed]] attacks had a speed penalty when attacking with a shield equipped.
 +
*Prior to [[0.16]], the amount of skill required to negate penalties for wearing a shield was more complex.
  
 
==References==
 
==References==
 
<references/>
 
<references/>
  
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==History==
+
[[Category:Items]]
−
 
+
[[Category:Shields]]
−
[[Category:Game mechanics]]
 

Revision as of 01:39, 13 April 2022

Version 0.28: This article may not be up to date for the latest stable release of Crawl.
“Let who will boast their courage in the field,

I find but little safety from my shield.
Nature's, not honour's, law we must obey:
This made me cast my useless shield away,
And by a prudent flight and cunning save
A life, which valour could not, from the grave.
A better buckler I can soon regain;
But who can get another life again?”
-Archilochos. 7th cent. B.C. trans. William H. Goodwin, 1878.

Shields are a kind of armour worn on one hand, preventing the use of two-handed weapons; they make use of the Shields skill. Unlike other armour, shields increase a character's SH defense, giving you a chance at blocking physical (and some magical) attacks entirely. There are four types of shield, in order of size:

Some magical effects can also increase your SH score.

Shield Penalties

Wearing a shield also gives penalties to attack speed, EV, and spellcasting. While the penalty for wearing a small buckler is almost negligible, a tower shield can seriously slow your attacks and make spellcasting unreliable.

Specifically, your shield penalty is 2/5 * encumbrance^2 / (20 - 3 * size_factor) * (27 - shield_skill) / 27[1]. This is your penalty to your evasion, which gets used to calculate everything else. This means that larger species can wield shields more comfortably, while anyone can eliminate shield penalty by maxing out the Shields skill.

Shield type Encumbrance
Buckler 5
Kite shield 10
Tower shield 15
Size Races Size factor
Little Spriggan +4
Small Kobold +2
Normal most races 0
Normal
(strong arms)		 Formicid -2
Large
(normal torso)		 Palentonga, Naga -2
Large Ogre, Troll -2

When attacking with any kind of weapon (including unarmed), if you are wearing a shield and your Shield penalty is greater than zero, the game throws two dice with (Shield penalty) sides. The smaller value rolled is added to your attack delay.

Egos

All three types of shields can spawn with the following egos[2]:

Shields of cold and fire resistance can occasionally be found in ice caves and volcanoes.

Blocking

Effect

It's possible to block a melee attack or a ranged projectile attack if you wear a shield of some kind or are under the effect of a magical shield (amulet of reflection, Qazlal's Storm Shield, or the Shining One's Divine Shield) or have the Large Bone Plates mutation. Your ability to block missiles doesn't benefit from missile-repelling effects like a scarf of repulsion, and you cannot benefit from any form of shield while you are confused.

All melee attacks can be blocked (except for successful stabs), but many ranged attacks are unblockable:

Some examples of ranged attacks that can be blocked:

If the attacker's pierce value is less than the defender's blocking value (see below for details), the attack does no damage. Shield blocking is done before rolling your evasion or your AC, but if you have already blocked some attacks in that turn, your blocking ability will be decreased greatly.

Calculation

The defender's blocking value depends on the nature of the shield:

Physical shields: 

SH = Block × (1 + Shield skill/40)
+ Enchantment bonus + Stat bonus 
+ min(0.38×Shield skill, .57 + 0.19×Shield skill)

and then on top of either of those: 

+ Divine shield bonus
+ Qazlal shield bonus
+ Mutation bonus
+ Amulet of reflection bonus
+ Any SH bonus from artifacts

For a physical shield (Buckler, Kite Shield, and Tower Shield), Block is the shield's blocking value, equal to the base shield bonus (3 for Buckler, 8 for Kite Shield, 13 for Tower Shield), modified by a size factor:

Size Races Buckler Kite Shield Tower shield
Little Spriggan +2 - -
Small Kobold +1 +0.5 -
Normal most races 0 0 0
Normal
(strong arms)		 Formicid 0 0 0
Large
(normal torso)		 Palentonga, Naga 0 0 0
Large Ogre, Troll - -0.5 0
  • Stat bonus is DEX * 38 * (base_shield + 13) / 26 ,
  • The Shining One's Divine shield bonus is based on Invocations skill.

The resulting value is rounded to the nearest integer and displayed as the player's SH value.

The attacker's pierce value is equal to: 

1d(15 + to hit/2 + 5×past_blocks^2) - 1 (melee attacks)

1d(1.3×to hit    + 5×past_blocks^2) - 1 (ranged attacks)

"To hit" is the monster's To hit value (based primarily on the monster's HD, type, and weapon accuracy) and "past_blocks" is the number of attacks already successfully blocked in the current turn.

The defender's blocking value is equal to: 

2d(2×SH)/6 - 1.3 (Divided by 3 against melee attacks from invisible opponents)

If this value is greater or equal than the attacker's pierce value, the attack is blocked.

History

  • Prior to 0.28, the two larger shields used Strength and Dexterity to determine SH, and shields had a to-hit penalty. The penalty formula changed; before, certain skill thresholds (4 skill for buckler, 15 for kite shield, 25 for tower shield) negated it.
  • In 0.27, the shield penalty was increased.
  • Prior to 0.25, kite shields were known as just "shields" and tower shields were called "large shields".
  • Prior to 0.17, unarmed attacks had a speed penalty when attacking with a shield equipped.
  • Prior to 0.16, the amount of skill required to negate penalties for wearing a shield was more complex.

References

  1. ↑ player.cc:5587 (0.28.0)
  2. ↑ makeitem.cc:768 (0.28.0)
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