BohdanQQ

A quick info dump/set of comments regarding the spellcasting series of the League of Legends techblog (24. April 2024). There are some very interesting tiny details!

Spell "buffering"

• is actaully internally called "Postponed Spells"!
• client side validation succeeds a majority of the time even when a spell can’t be cast server side
  • some spells may refund mana, so they send some spells anyway even if the client says you have no mana
  • still, the "no-mana" sound is played... interesting
• the extension of the "postponed spell" system reveals some interesting logic timing information about how the game handles spells
  • look for the passage starting with What the flub?

Spell Slots

• spells are mapped to slots
• slots are labeled with a number, 0 - 64
  • QWER mapped to 0-3
  • 63 is passive
  • 64 is basic attack
  • interesting choice of number range? why 0-64? what does this say about the data types they use?

"Flubbing"

For certain spells, you can queue up casting a spell a little bit before it comes off cooldown, which is a form of flub prevention.

Latency hiding

Since the implementation of client-side spellbook override, we no longer require a cast time to hide the latency between client and server.

• I just never thought of this as latency hiding, it makes perfect sense, just never crossed my mind - I just took if for granted and it just took me by surprise

Haha, an engineer

...let’s fill our palette with how spellcasting works in league of legends.

• name of the primary product in lower case, very "dev/engineer-y" of the author :D

"Thinking I found an exploit"

Combination of these two snippets had me worried:

• Once in the override state, we listen for new inputs and send a spell request to the server according to the additional input and the spellbook we’re in.

• The server would receive this packet, locate QQ, and put it on slot 0 (Q slot). Then the server will cast QQ and let the client know that a spellcast has been successfully casted.

My initial thoguht was: Do they not validate whether the specific combo is valid?

Later they of course expand on this: The reason is hackers can technically send fake spell request packets and the server will accept it.

Reusing the spellbook override

• for champs such as Nidalee/Jayce/Aphelios

The conversion does need some legwork, but the benefit would be that shapeshifters could buffer additional spells so their combos get even smoother.

• that is interesting, does this mean they could not buffer spells in-between forms?

I HATE CLAMPING

One thing that came up during the development process of Hwei is the custom settings for “Move To Cast”, which currently exists as an in-game option “Clamp cast target location within max range”! When enabled, spells will auto cast at the maximum range if your cursor is out of range of the spell, avoiding walking to cast.

HOLY SHIT I REMEMBER THIS. Due to the inconsistency regarding this "clamping", some champions became, from patch to patch, worse/better to play! I prefer the non-clamping version as you can test, for example, the width/AOE range of a cast by hovering over some location outside your range (ofc with quickcast disabled). I basically feel very restricted when the cast indicator is "limited" (clamped) like that.