Spell Success - Revision history

imported>Hordes: 0.34

2026-02-14T20:37:18Z

0.34

← Older revision		Revision as of 20:37, 14 February 2026
(No difference)

imported>Hordes: 0.34

2026-02-14T20:37:18Z

0.34

← Older revision		Revision as of 20:37, 14 February 2026
(No difference)

imported>Hordes: 0.34

2026-02-14T20:37:18Z

0.34

← Older revision		Revision as of 20:37, 14 February 2026
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	{{~~version032~~}}		{{version034}}
	{\| style="float: right;"		{\| style="float: right;"
	\| __TOC__		\| __TOC__
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	The following modifiers are added after the STEPPED DOWN failure rates above. However, it is still considered the ''raw spell failure chance'', which is adjusted by a sigmoid function later.<ref>{{source ref\|0.32.1\|spl-cast.cc\|461}}</ref>		The following modifiers are added after the STEPPED DOWN failure rates above. However, it is still considered the ''raw spell failure chance'', which is adjusted by a sigmoid function later.<ref>{{source ref\|0.32.1\|spl-cast.cc\|461}}</ref>

	'''~~Positive~~ (+spell failure):'''		Additive and subtractive modifiers are applied first, then multiplicative modifiers (like Vehumet and Wizardry) are applied afterwards.<ref>{{source ref\|0.34.0\|spl-cast.cc\|534}}</ref>

			'''Additive (+spell failure):'''
	*[[Wild Magic (mutation)\|Wild Magic]]: +4% per level		*[[Wild Magic (mutation)\|Wild Magic]]: +4% per level
	*Disrupted Magic (-Wiz) [[Ru\|sacrifice]]: +4% per level		*Disrupted Magic (-Wiz) [[Ru\|sacrifice]]: +4% per level
	*[[Orb]] of [[energy]]: +10%		*[[Orb]] of [[energy]]: +10%
	**[[Crystal ball of Wucad Mu]]: +10%
	*[[Vertigo]]: +7%		*[[Vertigo]]: +7%

	'''Negative (-spell failure):'''		'''Negative (-spell failure):'''
	*[[Subdued Magic]]: -2% per level		*[[Subdued Magic]]: -2% per level
	*[[Wizardry]]: multiplied by ×<code>6 / (7 + sources)</code>%, assuming you have at least one source. (×75% for Wiz x1, ×66.6% for Wiz x2, and so on.)
	*[[Vehumet]]: multiplied by ×66.6%.<ref>{{source ref\|0.32.1\|spl-cast.cc\|339}}</ref> (Note: this is not considered a source of wizardry, but it multiplicatively stacks with wizardry.)

	~~The wizardry~~ and Vehumet ~~multipliers are applied after all others~~.<ref>{{source ref\|0.32.1\|spl-cast.cc\|~~469~~}}</ref>		'''Multiplicative:''''
			*[[Wizardry]]: ×<code>6 / (7 + sources)</code>% for all spells, assuming at least 1 source. (×75% for Wiz x1, ×66.6% for Wiz x2, and so on.)
			*[[Vehumet]]: ×66.6% for [[destructive spell]]s.<ref>{{source ref\|0.32.1\|spl-cast.cc\|339}}</ref>
			*[[Transformation]]s:
			**[[Yak Form]]: ×66.6% for Ice Magic
			**[[Scarab Form]]: ×66.6% for Fire Magic
			**[[Sphinx Form]]: ×66.6% for Hexes
			*Armour [[ego]]s:
			**[[Command]]: ×<code>18/(18+Armour)</code> for Summonings
			**[[Death (ego)\|Death]]: ×50% for Necromancy
			**[[Resonance]]: ×66.6% for Forgecraft

			[[Revenant]]'s Enkindle modifier is <code>raw_failure * 0.75 - 5</code> and is applied after all other raw factors.

	After all modifiers have applied, you will get a cumulative ''raw spell failure chance''. This is converted into the final success via the function below.		After all modifiers have applied, you will get a cumulative ''raw spell failure chance''. This is converted into the final success via the function below.
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	\|}		\|}
	<nowiki></nowiki>SpellFailure required to reach a given raw fail chance, ''assuming you don't have any modifiers like [[wizardry]]''. E.g. if you have wizardry x1, having 1 SpellFailure = (28% 0.75) raw failure = 21% raw failure.		<nowiki></nowiki>SpellFailure required to reach a given raw fail chance, ''assuming you don't have any multiplicative modifiers like [[wizardry]]''. E.g. if you have wizardry x1, having 1 SpellFailure = (28% 0.75) raw failure = 21% raw failure.

	==Strategy==		==Strategy==

Hordes at 09:09, 24 October 2025

2025-10-24T09:09:56Z

← Older revision		Revision as of 09:09, 24 October 2025
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	==Strategy==		==Strategy==
	It is debatable whether these formulae are of any practical use during a game.		It is debatable whether these formulae are of any practical use during a game. Simply training a skill, checking the spell failure every so often, and stopping once a satisfactory failure% is achieved is generally enough.

	It may be nice to know a few things from a strategic point of view.		It may be nice to know a few things from a strategic point of view.
	*High level spells take a massive amount of XP to train, and it can be useful to know how many levels you'd need.		*High level spells take a massive amount of XP to train, and it can be useful to know how many levels you'd need up front.
	*You can quantize your level of armour [[encumbrance]]. A caster could say "a set of [[fire dragon scales]] gives a spell penalty equal to 6 levels of each spell school". Then, you could determine if wearing FDS is worth it, both short-term ("can I cast a spell in this ''right now''?") and long-term ("can I cast a spell in this ''when I reach Zot''?").		*You can quantize your level of armour [[encumbrance]]. A caster could say "a set of [[fire dragon scales]] gives a spell penalty equal to 6 levels of each spell school". Then, you could determine if wearing FDS is worth it, both short-term ("can I cast a spell in this ''right now''?") and long-term ("can I cast a spell in this ''when I reach Zot''?").
	*You can calculate the relative value of a skill. For example, you can see when a level of <Spell School> would be more valuable than a level of Armour skill, or when a point of [[strength]] is worth more than a point of [[intelligence]].		*You can calculate the relative value of a skill. For example, you can see when a level of <Spell School> would be more valuable than a level of Armour skill, or when a point of [[strength]] is worth more than a point of [[intelligence]].

Hordes: /* Final Step */

2025-07-30T11:11:01Z

Final Step

← Older revision		Revision as of 11:11, 30 July 2025
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	{\| class="prettytable" style="text-align: center" border=1		{\| class="prettytable" style="text-align: center" border=1
	\|-		\|-
	!SpellFailure*!!Raw fail chance!!Actual fail chance		!SpellFailure (unmodded)*!!Raw fail chance!!Actual fail chance
	\|-		\|-
	\|13\|\|32%\|\|14.9%		\|13\|\|32%\|\|14.9%

Patrick2011b: commit 20a70ad added the spellFailure cap in 0.26

2025-04-08T22:04:49Z

commit 20a70ad added the spellFailure cap in 0.26

← Older revision		Revision as of 22:04, 8 April 2025
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	==History==		==History==
	*Prior to [[0.31]], the raw failure rate multiplier from wizardry/Vehumet was capped at 50%. Therefore, you could only have a maximum of 5 stacks of wizardry, or 1 stack of wizardry with Vehumet's bonus. Also, some [[transmutations]] increased your spell failure: [[Spider Form]] (+10%) and [[Blade Hands (spell)\|Blade Hands]] (+20%).		*Prior to [[0.31]], the raw failure rate multiplier from wizardry/Vehumet was capped at 50%. Therefore, you could only have a maximum of 5 stacks of wizardry, or 1 stack of wizardry with Vehumet's bonus. Also, some [[transmutations]] increased your spell failure: [[Spider Form]] (+10%) and [[Blade Hands (spell)\|Blade Hands]] (+20%).
			*Prior to [[0.26]], spellFailure was not capped.
	Prior to [[0.22]], spell_schools went through a stepdown, <code>50 log2(1 + spell_schools/50)</code>, which penalized the caster if <code>(Spellcasting/2) + (2* AvgSpellSchool) > 50</code>. However, spellFailure for level 9 spells was 330 instead of 340.		Prior to [[0.22]], spell_schools went through a stepdown, <code>50 log2(1 + spell_schools/50)</code>, which penalized the caster if <code>(Spellcasting/2) + (2* AvgSpellSchool) > 50</code>. However, spellFailure for level 9 spells was 330 instead of 340.
	*Prior to [[0.20]], the [[#Step down\|Step down]] function was different, relying on breakpoints rather than a polynomial. Also, more breakpoints existed elsewhere in the spell failure calculation.		*Prior to [[0.20]], the [[#Step down\|Step down]] function was different, relying on breakpoints rather than a polynomial. Also, more breakpoints existed elsewhere in the spell failure calculation.

Patrick2011b: spellFailure is capped at 210 before going through the stepdown; also update to 0.32

2025-04-08T21:54:31Z

spellFailure is capped at 210 before going through the stepdown; also update to 0.32

← Older revision		Revision as of 21:54, 8 April 2025
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	{{~~version031~~}}		{{version032}}
	{\| style="float: right;"		{\| style="float: right;"
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	The source code talks in terms of chance of ''failure'', not success. Therefore, we want the spellFailure chance to be as low as possible - in fact, to reach a 0% failure rate, your chance to fail has to be '''negative'''. More on that below.		The source code talks in terms of chance of ''failure'', not success. Therefore, we want the spellFailure chance to be as low as possible - in fact, to reach a 0% failure rate, your chance to fail has to be '''negative'''. More on that below.

	The base failure before ''any'' modifiers is as follows:<ref>{{source ref\|0.30.0\|spl-cast.cc\|~~406~~}}</ref>		The base failure before ''any'' modifiers is as follows:<ref>{{source ref\|0.32.1\|spl-cast.cc\|401}}</ref>

	spellFailure = 60		spellFailure = 60
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	+ Encumbrance penalties		+ Encumbrance penalties

	* 60 is an arbitrary base chance of failure.		*60 is an arbitrary base chance of failure.
	* Increasing intelligence and spell skills (skills respective to the spell ''and'' [[Spellcasting]]) will decrease failure.		*Increasing intelligence and spell skills (skills respective to the spell ''and'' [[Spellcasting]]) will decrease failure.
	* Higher level spells are more difficult, wearing armour/shields make it more difficult.		*Higher level spells are more difficult, wearing armour/shields make it more difficult.

	=== Spell skills ===		spellFailure is capped at 210 at this point.<ref>{{source ref\|0.32.1\|spl-cast.cc\|441}}</ref>
	"Spell_skills" takes into account Spellcasting and an average of a spell's schools (e.g. a Conjurations / Fire spell will take the average of the [[Conjurations]] skill and [[Fire Magic]] skill). This is calculated with the following equation:<ref>{{source ref\|0.30.0\|spl-cast.cc\|~~413~~}}</ref>
	<ref>{{source ref\|0.30.0\|spl-cast.cc\|377}}</ref>		===Spell skills===
			"Spell_skills" takes into account Spellcasting and an average of a spell's schools (e.g. a Conjurations / Fire spell will take the average of the [[Conjurations]] skill and [[Fire Magic]] skill). This is calculated with the following equation:<ref>{{source ref\|0.32.1\|spl-cast.cc\|408}}</ref>
			<ref>{{source ref\|0.32.1\|spl-cast.cc\|377}}</ref>
	spell_skills = [Spellcasting / 2] + [Average(Skill_level) * 2]		spell_skills = [Spellcasting / 2] + [Average(Skill_level) * 2]

	=== Spell difficulty ===		===Spell difficulty===
	Higher level spells are more difficult. Each level of spell adds a number to your spell failure rate:<ref>{{source ref\|0.30.0\|spl-cast.cc\|~~422~~}}</ref>		Higher level spells are more difficult. Each level of spell adds a number to your spell failure rate:<ref>{{source ref\|0.32.1\|spl-cast.cc\|417}}</ref>

	spellDifficulty = 3 (level 1)		spellDifficulty = 3 (level 1)
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	340 (level 9) (+80)		340 (level 9) (+80)

	=== Encumbrance penalties ===		===Encumbrance penalties===

	Both Armour and Shield penalties for spells are derived from their [[EV]] penalties. First, calculate the ev penalty, then calculate the spell penalty. Armour and Shields do not influence each other.		Both Armour and Shield penalties for spells are derived from their [[EV]] penalties. First, calculate the ev penalty, then calculate the spell penalty. Armour and Shields do not influence each other. [[Mountain Dwarf\|Mountain Dwarves]] treat the armour encumbrance as half of its normal value.

	'''Armour'''<ref>{{source ref\|0.30.0\|player.cc\|~~5723~~}}</ref><ref>{{source ref\|0.30.0\|player.cc\|~~2131~~}}</ref>		'''Armour'''<ref>{{source ref\|0.32.1\|player.cc\|6147}}</ref><ref>{{source ref\|0.32.1\|player.cc\|2265}}</ref>

	ev penalty = 1/225 * [[encumbrance]]^2 * (90 - 2 * [[Armour (skill)\|armour_skill]]) / ([[str]] + 3)		ev penalty = 1/225 * [[encumbrance]]^2 * (90 - 2 * [[Armour (skill)\|armour_skill]]) / ([[str]] + 3)
	spell penalty = 19 * ev penalty		spell penalty = 19 * ev penalty

	'''Shield'''<ref>{{source ref\|0.30.0\|player.cc\|~~5739~~}}</ref><ref>{{source ref\|0.30.0\|player.cc\|~~2134~~}}</ref>		'''Shield'''<ref>{{source ref\|0.32.1\|player.cc\|6163}}</ref><ref>{{source ref\|0.32.1\|player.cc\|2273}}</ref>

	ev penalty = 2/5 * [[Shields#EV_Penalty\|encumbrance]]^2 / (5 + str) * (27 - [[Shields_(skill)\|shield_skill]]) / 27		ev penalty = 2/5 * [[Shields#EV_Penalty\|encumbrance]]^2 / (5 + str) * (27 - [[Shields_(skill)\|shield_skill]]) / 27
	spell penalty = 19 * ev penalty		spell penalty = 19 * ev penalty

	== Step down ==		==Step down==
	At this point, the spell failure is put through a complicated post-processing curve:<ref>{{source ref\|0.30.0\|spl-cast.cc\|~~463~~}}</ref>		At this point, the spell failure is put through a complicated post-processing curve:<ref>{{source ref\|0.32.1\|spl-cast.cc\|458}}</ref>

	(x^3 + 426x^2 + 82670x + 6983254) / 262144 IF spellFailure < 43		(x^3 + 426x^2 + 82670x + 6983254) / 262144 IF spellFailure < 43
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	==Modifiers==		==Modifiers==
	The following modifiers are added after the STEPPED DOWN failure rates above. However, it is still considered the ''raw spell failure chance'', which is adjusted by a sigmoid function later.<ref>{{source ref\|0.30.0\|spl-cast.cc\|~~466~~}}</ref>		The following modifiers are added after the STEPPED DOWN failure rates above. However, it is still considered the ''raw spell failure chance'', which is adjusted by a sigmoid function later.<ref>{{source ref\|0.32.1\|spl-cast.cc\|461}}</ref>

	'''Positive (+spell failure):'''		'''Positive (+spell failure):'''
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	*[[Subdued Magic]]: -2% per level		*[[Subdued Magic]]: -2% per level
	*[[Wizardry]]: multiplied by ×<code>6 / (7 + sources)</code>%, assuming you have at least one source. (×75% for Wiz x1, ×66.6% for Wiz x2, and so on.)		*[[Wizardry]]: multiplied by ×<code>6 / (7 + sources)</code>%, assuming you have at least one source. (×75% for Wiz x1, ×66.6% for Wiz x2, and so on.)
	*[[Vehumet]]: multiplied by ×66.6%.<ref>{{source ref\|0.30.0\|spl-cast.cc\|~~335~~}}</ref> (Note: this is not considered a source of wizardry, but it multiplicatively stacks with wizardry.)		*[[Vehumet]]: multiplied by ×66.6%.<ref>{{source ref\|0.32.1\|spl-cast.cc\|339}}</ref> (Note: this is not considered a source of wizardry, but it multiplicatively stacks with wizardry.)

	The wizardry and Vehumet multipliers are applied after all others.<ref>{{source ref\|0.30.0\|spl-cast.cc\|~~475~~}}</ref>		The wizardry and Vehumet multipliers are applied after all others.<ref>{{source ref\|0.32.1\|spl-cast.cc\|469}}</ref>

	After all modifiers have applied, you will get a cumulative ''raw spell failure chance''. This is converted into the final success via the function below.		After all modifiers have applied, you will get a cumulative ''raw spell failure chance''. This is converted into the final success via the function below.

	==Final Step==		==Final Step==
	In short, the game doesn't compare your raw failure chance with a number from 0 to 99. Instead, it compares the raw failure to the sum of three numbers divided by three.<ref>{{source ref\|0.30.0\|spl-cast.cc\|~~2533~~}}</ref>		In short, the game doesn't compare your raw failure chance with a number from 0 to 99. Instead, it compares the raw failure to the sum of three numbers divided by three.<ref>{{source ref\|0.32.1\|spl-cast.cc\|2636}}</ref>
	(1d101 + 1d101 + 1d100 - 3)/3 < fail chance		(1d101 + 1d101 + 1d100 - 3)/3 < fail chance

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	<nowiki></nowiki>SpellFailure required to reach a given raw fail chance, ''assuming you don't have any modifiers like [[wizardry]]''. E.g. if you have wizardry x1, having 1 SpellFailure = (28% 0.75) raw failure = 21% raw failure.		<nowiki></nowiki>SpellFailure required to reach a given raw fail chance, ''assuming you don't have any modifiers like [[wizardry]]''. E.g. if you have wizardry x1, having 1 SpellFailure = (28% 0.75) raw failure = 21% raw failure.

	== Strategy ==		==Strategy==
	It is debatable whether these formulae are of any practical use during a game.		It is debatable whether these formulae are of any practical use during a game.

Hordes: /* Analysis */

2025-03-16T12:25:31Z

Analysis

← Older revision		Revision as of 12:25, 16 March 2025
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	===Skill Req'd to Cast L9 Spells===		===Skill Req'd to Cast L9 Spells===
	Say you wanted to [[Fire Storm]] reliably. For sake of example, ~~we're trying~~ to reach a 10% failure rate. ~~You~~ can look at the table above~~: to~~ get a 10% actual failure rate, you'd need 28% raw failure. ~~If you have no wizardry,~~ 28% raw failure = 1 SpellFailure.		Say you wanted to [[Fire Storm]] reliably. For sake of example, assume you want to reach a 10% failure rate. To do this, you can look at the table above.
			*To get a 10% "actual" failure rate, you'd need to reach 28% raw failure rate.
			*To get a 28% raw failure rate, before accounting for wizardry, you'd need to reach 1 SpellFailure.

	Using the [[#Base Chance\|SpellFailure]] calculations at the top of the page, you can calculate what's needed to get to 1 SpellFailure. For this example, assume you have 30 intelligence, no wizardry, and 0 encumbrance from armour/shields.		Using the [[#Base Chance\|SpellFailure]] calculations at the top of the page, you can calculate what's needed to get to 1 SpellFailure. For this example, assume you have 30 intelligence, no wizardry, and 0 encumbrance from armour/shields.
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	*'''Vehumet + Wizardry x1''': {14 Spellcasting, 20.2 avg_skill}, {18.9 Spellcasting, 18.9 avg_skill}		*'''Vehumet + Wizardry x1''': {14 Spellcasting, 20.2 avg_skill}, {18.9 Spellcasting, 18.9 avg_skill}

	These numbers apply to any level 9 spell in the game, not just Fire Storm... ~~again,~~ ''assuming you have 30 int / 0 encumbrance''. If you're wearing [[swamp dragon scales]] and a [[kite shield]], for instance, it'll take more skill to cast. Change the values of spell level, intelligence, encumbrance as you see fit.		These numbers apply to any level 9 spell in the game, not just Fire Storm... ''assuming that you have 30 int / 0 encumbrance''. If you're wearing [[swamp dragon scales]] and a [[kite shield]], for instance, it'll take more skill to cast. Change the values of spell level, intelligence, encumbrance as you see fit.

	===Measuring Encumbrance===		===Measuring Encumbrance===

Hordes: /* Final Step */

2024-10-25T10:14:45Z

Final Step

← Older revision		Revision as of 10:14, 25 October 2024
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	(1d101 + 1d101 + 1d100 - 3)/3 < fail chance		(1d101 + 1d101 + 1d100 - 3)/3 < fail chance

	This is equivalent to applying this transformation to the chance of failure:		This is equivalent to applying this transformation to the chance of failure (x-axis: raw failure rate; y-axis: actual fail %):

	[[Image:Spell_success_transformation.png]]		[[Image:Spell_success_transformation.png]]
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	{\| class="prettytable" style="text-align: center" border=1		{\| class="prettytable" style="text-align: center" border=1
	\|-		\|-
	!SpellFailure ~~Req'd~~*!!Raw fail chance!!Actual fail chance		!SpellFailure*!!Raw fail chance!!Actual fail chance
	\|-		\|-
	\|13\|\|32%\|\|14.9%		\|13\|\|32%\|\|14.9%

imported>ForkInBrain: 0% success rate -> 0% failure rate

2024-03-27T04:01:23Z

0% success rate -> 0% failure rate

← Older revision		Revision as of 04:01, 27 March 2024
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	==Base Chance==		==Base Chance==
	The source code talks in terms of chance of ''failure'', not success. Therefore, we want the spellFailure chance to be as low as possible - in fact, to reach a 0% ~~success~~ rate, your chance to fail has to be '''negative'''. More on that below.		The source code talks in terms of chance of ''failure'', not success. Therefore, we want the spellFailure chance to be as low as possible - in fact, to reach a 0% failure rate, your chance to fail has to be '''negative'''. More on that below.

	The base failure before ''any'' modifiers is as follows:<ref>{{source ref\|0.30.0\|spl-cast.cc\|406}}</ref>		The base failure before ''any'' modifiers is as follows:<ref>{{source ref\|0.30.0\|spl-cast.cc\|406}}</ref>