Programming Pokémon Showdown Damage Calculator

[Roldski32]

One bug I discovered recently, the damage didn't changed if i edited the stats of the pokemon like they still keep the original stat:

I was trying to edited the stats for some Other Metagames like 350 Cup.

 

[pre]

One bug I discovered recently, the damage didn't changed if i edited the stats of the pokemon like they still keep the original stat:

Thanks for reporting! Fixed.

 

[DaWoblefet]

A wide number of issues with the current damage calculator exist which largely arise at a result of not being up-to-date with Generation 7 modifier order. I'll go through the non-Gen 7 issues first, then I'll address the Gen 7-specific bugs. Assume in these damage calculations both targets are at level 100.

• Parental Bond

Parental Bond should run two independent strikes to calculate damage, not do a trivial damage = damage * modifier. Parental Bond causes the move to run an entirely new damage calculation and applies the baby hit modifier in between the spread move modifier and the weather modifier. As a result, there should be two independent sets of damage rolls displayed, as well as percent to KO being based on 256 combinations of damage rolls, not 16. Displaying it as a combination would require displaying potentially 256 damage rolls, so most damage calculators that implement Parental Bond accurately do something like this:

Example of accurate output

Accurate output:
152 Atk Parental Bond Kangaskhan-Mega Frustration vs. 252 HP / 152+ Def Amoonguss: 190-225 (43.98 - 52.08%) -- 6.65% chance to 2HKO (1089/16384)
(1st Hit: 153, 154, 156, 157, 159, 162, 163, 165, 166, 168, 171, 172, 174, 175, 177, 180; 2nd Hit: 37, 37, 39, 39, 39, 40, 40, 40, 40, 42, 42, 42, 43, 43, 43, 45)

PS damage calc:
152 Atk Parental Bond Kangaskhan-Mega Frustration vs. 252 HP / 152+ Def Amoonguss: 191-225 (44.2 - 52%) -- 12.5% chance to 2HKO
Possible damage amounts: (191, 192, 195, 196, 198, 202, 203, 206, 207, 210, 213, 215, 217, 218, 221, 225)

In addition, certain secondary effects that apply if a target has taken damage / target is not at full HP should be factored into the baby hit's calculation. These notably include: Shadow Shield / Multiscale, Assurance, Power-Up Punch.

Example of accurate output

Accurate output:
252 Atk Parental Bond Kangaskhan-Mega Crunch vs. 0 HP / 0 Def Shadow Shield Lunala: 280-334 (67.47 - 80.48%) -- guaranteed 2HKO
(1st Hit: 188, 190, 192, 194, 196, 198, 202, 204, 206, 208, 210, 212, 214, 216, 218, 222; 2nd Hit: 92, 96, 96, 96, 96, 100, 100, 100, 104, 104, 104, 104, 108, 108, 108, 112)

PS damage calc:
252 Atk Parental Bond Kangaskhan-Mega Crunch vs. 0 HP / 0 Def Shadow Shield Lunala: 235-277 (56.6 - 66.7%) -- guaranteed 2HKO
Possible damage amounts: (235, 237, 240, 242, 245, 247, 252, 255, 257, 260, 262, 265, 267, 270, 272, 277)

• Unnecessary 0x1000 modifiers: these would affect cases of damage overflow (and generally speaking won't affect the calculation in any normal cases anyway, so are unnecessary)

- Soul Dew when not a Lati twin
- STAB when user doesn't have STAB

Generation 7 modifier order

From a cursory glance, the conditions for checking if a modifier should be applied is correct; it's moreso the order. The listed modifiers (BP, Attack, Defense, final modifiers, general damage modifiers), are taken from OZY's research, which is considered to be the authoritative research for Gen 7 and is what the simulator itself is using (or minimally should be using). I have listed these in the order they should be applied. If you have any questions about what I mean, or need test cases, let me know. Modifiers that are incorrect in the PS damage calculator are bolded.

• Gen 7 BP modifiers

1. Aura Break - 0xC00
2. Rivalry and gender is not the same - 0xC00
3. -ate Abilities - 0x1333
4. Iron Fist - 0x1333
5. Reckless - 0x1333
6. Rivalry and gender is the same - 0x1400
7. Battery - 0x14CD
8. Sheer Force - 0x14CD
9. Sand Force - 0x14CD
10. Analytic - 0x14CD
11. Tough Claws - 0x14CD
12. Fairy Aura / Dark Aura - 0x1548
13. Technician - 0x1800 (note that Technician will check if the previous modifiers would have pushed this above/below 60 BP)
14. Flare Boost - 0x1800
15. Toxic Boost - 0x1800
16. Strong Jaw - 0x1800
17. Mega Launcher - 0x1800
18. Heatproof - 0x800
19. Dry Skin - 0x1400
20. Muscle Band - 0x1199
21. Wise Glasses - 0x1199
22. Type-boosting items - 0x1333
23. Orbs - 0x1333
24. Gems - 0x14CD
25. Solar Beam / Solar Blade - 0x800
26. Me First - 0x1800
27. Knock Off - 0x1800
28. Helping Hand - 0x1800
29. Charge - 0x2000
30. Facade - 0x2000
31. Brine - 0x2000
32. Venoshock - 0x2000
33. Retaliate - 0x2000
34. Fusion Bolt / Fusion Flare - 0x2000
35. Grassy Terrain / Misty Terrain (defensive) - 0x800
36. Electric / Grassy / Psychic Terrain (offensive) - 0x1800
37. Mud Sport / Water Sport - 0x548

If base power exceeds 16 bits after the 1 BP check (i.e. greater than 65535), mod by 65536. Source.

• Gen 7 Attack modifiers

+6/-6 boosts/drops
Hustle

1. Slow Start (of note, don't forget that special Z-moves are affected by Slow Start) - 0x800
2. Defeatist - 0x800
3. Flower Gift - 0x1800
4. Guts - 0x1800
5. Overgrow / Blaze / Torrent / Swarm - 0x1800
6. Flash Fire - 0x1800
7. Solar Power - 0x1800
8. Plus / Minus - 0x1800
9. Steelworker - 0x1800
10. Huge Power / Pure Power - 0x2000
11. Water Bubble (offensive) - 0x2000
12. Stakeout - 0x2000
13. Thick Fat - 0x800
14. Water Bubble (defensive) - 0x800
15. Choice Band / Choice Specs - 0x1800
16. Thick Club - 0x2000
17. Deep Sea Tooth - 0x2000
18. Light Ball - 0x2000

If the attack exceeds 16 bits after the 1 attack check (i.e. greater than 65535), mod by 65536. Source.

• Gen 7 Defense modifiers

+6/-6 boosts/drops
Sandstorm & Rock-types

1. Flower Gift - 0x1800
2. Marvel Scale - 0x1800
3. Grass Pelt - 0x1800
4. Fur Coat - 0x2000
5. Eviolite - 0x1800
6. Assault Vest - 0x1800
7. Deep Sea Scale - 0x2000
8. Metal Powder - 0x2000

If the attack exceeds 16 bits after the 1 defense check (i.e. greater than 65535), mod by 65536. Source.

• General damage modifiers

After calculating the base damage, apply these modifiers in order, according to OZY research.

1. Spread move - 0xC00
2. Parental Bond - 0x400
3. Weather - 0x1800 for boosting, 0x800 for weakening
4. Crit - 0x1800
5. Random factor
6. STAB (Adaptability) - 0x1800 (0x2000)
7. Type effectiveness - So long as we only support two types, 0.25x-4x
8. Burn - 0x800
9. Final damage modifiers
10. Z-moves into Protect - 0x400
11. 1 damage modifier
12. 16 bit constraint (maximum damage should never be higher than 65535)

• Final damage modifiers

OZY research etc.

1. Screens - Singles = 0x800, Doubles = 0xAAC
2. Neuroforce - 0x1400
3. Sniper - 0x1800
4. Tinted Lens - 0x2000
5. Multiscale / Shadow Shield - 0x800
6. Fluffy (contact moves) - 0x800
7. Friend Guard - 0xC00
8. Solid Rock / Filter / Prism Armor - 0xC00
9. Fluffy (Fire-type moves) - 0x2000
10. Metronome (item) - you have this right
11. Expert Belt - 0x1333
12. Life Orb - 0x14CC
13. Resist Berries - 0x800
14. Doubled-power moves - 0x2000

• 32-bit multiplication overflow

If a calculation ever exceeds 2^32 - 1, mod by 2^32. This has been proven to be possible during the base damage calculation, when applying any modifier after the base damage, during the random factor, and even during trivial modifiers (e.g. if there are no final modifiers, an implicit 4096/4096 is applied). This is in addition to the 16 bit constraints listed for BP, Attack, Defense, and damage at the very end.

• Weight calculations

See SadisticMystic's research.

1. Apply all Autotomizes (there is a weight minimum of 0.1kg).
2. Apply Heavy Metal (there is no weight maximum)
3. Apply Light Metal and Float Stone. There is still a weight minimum of 0.1kg. If the calculation results in a weight that extends to two decimal places, "floor" to one decimal place (e.g. 10.25 = 10.2, 10.24 = 10.2, and 10.26 = 10.2).

• Speed calculations

See DaWoblefet's research.

1. Apply boosts/drops (+6/-6) and floor.
2. Apply all other Speed modifiers except paralysis and pokeRound.
3. Apply paralysis and floor.

 

[0riion]

I noticed a few moves are not in the calculator like rollout

 

[pre]

If one selects the Heracross set for UU it sets the ability to Moxie when it should be Guts.

Thanks for the report - this is now fixed, along with zMoves not being able to cause critical hits.

 

[pre]

Magnemite and Magneton are defaulting to just electric and not electric/steel in the calculator (in every gen)

Fixed.

When I reduce the DVs for HP Water for this calculation the damage calculation doesn't change even though it should.

Changing your HP/Atk/Def should have no affect on a Special Attack if I'm not mistaken, so I assume you mean "The calculator does not update the Hidden Power's type and base power based on changes to DVs?" (If you look, its still HP Ice 70). In the particular case of your screenshot, I believe 7/14/13/15/15/15 would still be base power 70, and Water has the same type effectiveness against Aerodactyl as Ice, so the end result should be the same in this case?

Please correct me if I'm misunderstanding - I've filed a bug to have changes to DVs/IVs reflected as changes to the Hidden Power type/BP, but for now you'll need to adjust the BP and type manually using the drop downs beside the move. :(

Import feature won't recognize Gastrodon-East

Thanks. This isn't a regression, we've never supported this AFAICT. I've filed a bug to make sure we have import/export parity with the teambuilder on the client, but this is going to take some time to implement :(. In the meantime you're stuck changing 'Gastrodon-East' to 'Gastrodon' before importing, sorry.

 

[pre]

When I reduce the HP and Def DVs on Zapdos, Zapdos should be taking more damage from Aerodactyl's Ancient Power.

Fixed. Thank you for the bug report - really sorry you had to discover this in a battle! :(

 

[Roldski32]

Moves that lower user's stats (i.e. Leaf Storm, Superpower, Draco Meteor) seems to not working when clicking Twice or even 5 times to show the total damage output.

 

[pre]

i discovered an issue with the way stat boots and drops are measured in gsc. in gens 1 and 2 when you drop your speed stat by one stage it's dropped to 66/100 and not 67/100 like in gen 3 and above. the damage calc however implements 67/100 for gen 2

Thanks for the detailed bug report ("arrows and a GIF"!) - this is now fixed.

Mold Breaker should ignore unaware, but it currently does not in the calc:

252 Atk Mold Breaker Haxorus Devastating Drake (190 BP) vs. 252 HP / 252+ Def Quagsire: 271-321 (68.7 - 81.4%) -- guaranteed 2HKO after Leftovers recovery

+6 252 Atk Mold Breaker Haxorus Devastating Drake (190 BP) vs. 252 HP / 252+ Def Unaware Quagsire: 271-321 (68.7 - 81.4%) -- guaranteed 2HKO after Leftovers recovery

just throwing that out there

This should be fixed?

The calculator doesn't take in consideration Mold Breaker when against mons with Levitate

Hmm... I specifically made fixes to Mold Breaker yesterday, but maybe I didn't deploy the change. However, I've confirmed it appears fixed now:

damage calc stuck in "loading" for me. checked and javascript was enabled. all chrome settings at recommended. this has been going on for months

Try turning off all your extensions maybe (or an incognito window)?

 

[LucasBoat]

Mold breaker is ok when against Unaware, the problem persists when against Levitate tho

 

[pre]

Please see the screen shot I linked above in my edited post. But here's another one for you:

Please make sure you clear your cache/hard refresh to get the latest version of the calc!

 

[pre]

Is there a nodejs version? I'd really like to use this in my own project. I tried to convert it by hand, but it was taking forever, and once an update comes out, well, I'd be screwed.

There actually is now, soon to be released as @pokemon-showdown/calc on NPM.

 

[sumwun]

Low kick and grass knot are broken in DPP.

screenshot

 

[DaWoblefet]

Wring Out / Crush Grip use the wrong formula for damage; it should be scaling HP to 4096s.

Here's an accurate formula representation:

In JS, I'm pretty sure something like this would work:
Math.max(1, Math.floor(pokeRound((120 * 100 * Math.floor((defender.curHP * 4096) / defender.maxHP())) / 4096) / 100))

For a test case, Wring Out vs. 184/362 HP should have 60 BP, not 61 BP. The damage calculator currently returns this (incorrect):

0 SpA Smeargle Wring Out (61 BP) vs. 252 HP / 0 SpD Blissey: 9-12 (2.4 - 3.3%) -- possibly the worst move ever

 

[pre]

Low kick and grass knot are broken in DPP.

Fixed.

Wring Out / Crush Grip use the wrong formula for damage; it should be scaling HP to 4096s.

Thanks, I've fixed this by copying the base power formulas from the simulator for Gen 4 and Gen 5-7 respectively.

 

[edudittA]

I pasted an importable of a 1v1 team on the Import/Export text box, clicked the "Import" button, clicked on "Only show imported sets", and then tried to select a set from the newly imported Pokemon. It showed the Pokemon and the spread all right, but it doesn't seem to display the moves, but instead shows something like this

Why I spelt out each step of the process

[21:11:22] Attid(UwU)de: In the damage calc
[21:11:40] Attid(UwU)de: When I import set(s), the set moves are not loading
[21:12:13] jetou :https://www.smogon.com/forums/threads/3593546
[21:16:58] Attid(UwU)de:https://imgur.com/loeG2kJ This shod be proof enough, right?
[21:17:37] jetou : Yes, they can reproduce it on their end, granted you explain the reproduction steps well enough.

Just wanted to make sure I did everything correctly......

 

[Austin]

Some moves, like morning sun, are completely left out of the damage calculator because very few people want to know how much damage morning sun does.

This isn’t intended I’ll add the move

 

[Cuddly]

Some moves, like morning sun, are completely left out of the damage calculator because very few people want to know how much damage morning sun does.

This made me think about a potential new feature for the Damage Calculator with healing, stat raising moves, and Protect (although would probably be somewhat niche).
It's where you can calculate if a move would be a 2HKO, 3HKO, ect. when factoring in Protect, Leftovers, Wish, Recover, and Calm Mind/Curse.
This would be useful in those scenarios where you have use a move like Leaf Storm/Super Power against a wall with recover, or in those moments where 2 left over recoveries turn a 2HKO into a 3HKO.
It can also create the NKO (Never Knock Out) as a move may be too weak initially, the opponent can heal/boost off any potential damage, or when your stats are dropping.
This probably would be too much effort to code for such a niche idea, but it would be interesting.

 

[McMeghan]

Gen 3 doubles battle only apply a 25% reduction to spread moves damage when it should be 50%

 

[pre]

Gen 3 doubles battle only apply a 25% reduction to spread moves damage when it should be 50%

I think this may be a misconception? At least, it was for whoever wrote this comment in the Gen 3 mechanics code:

PS is 75% for all gens...

Marty / DaWoblefet - can you weigh in here?

 

[Marty]

Who wrote that comment...

It's well known that spread damage in Gen 3 is split between 100% damage for moves that target everyone (Earthquake, Explosion, etc.) and 50% damage for moves that only target both opponents (Razor Leaf, Surf, etc.). It's just not implemented yet, nor is the actual correct order for the Gen 3 damage formula in general.

 

[pre]

It's just not implemented yet, nor is the actual correct order for the Gen 3 damage formula in general.

Which brings up the question - if we fix the Gen 3 damage formula in the damage calc (which would require work beyond just this line, in the same way we still need to implement OZY's move order research in Gen 6/7), would we instead get people thinking its wrong compared to PS? (ie. is it better to be wrong and consistent with PS, where most people are going to be playing when using the calc, or correct but inconsistent and less useful when trying to determine how things will work on PS).

I think both the simulator and calc should be corrected (obviously), but the simulator is probably much higher value to fix first.

 

[Marty]

Which brings up the question - if we fix the Gen 3 damage formula in the damage calc (which would require work beyond just this line, in the same way we still need to implement OZY's move order research in Gen 6/7), would we instead get people thinking its wrong compared to PS?

I skimmed through the disassembly extremely quickly and compared to the damage calc code, and it appears that everything is already done in exactly the right order except for this specific line being wrong (move target "8" is both opponents, and only when two opponents exist) and physical attacks ensuring minimum 1 damage before the + 2 at the end, but no such check for special attacks.

 

[Honko]

Who wrote that comment...

It's well known that spread damage in Gen 3 is split between 100% damage for moves that target everyone (Earthquake, Explosion, etc.) and 50% damage for moves that only target both opponents (Razor Leaf, Surf, etc.). It's just not implemented yet, nor is the actual correct order for the Gen 3 damage formula in general.

Guilty! To be fair, nobody ever answered me about that one in this thread from 2014...

Glad it's finally being cleared up!

 

[Dragonmirror]

What i think is a bug with the +1 All Stats button
from what i understand it is supposed to emulate the effects of z-celebrate/hold hands/happy hour

When clicking on the button and then checking Stored Power, it shows its BP as 140 (and calcs 140 BP) when in game it should be 120. likely a bug not certain but im psure thats a mistake