Purpose of Cast speed.

[BadMedium]

I've yet to play a "caster" build, but between rogue, ranger and warrior I can't see any use for cast speed, even though rogue has a +cast speed per stack skill in their kit. Does it increase the speed of the cast animation? Fan of Knives (and every other ability across those three characters) comes out almost instantaneously, so what is the purpose of cast speed?

[div.ide]

From stat description alone, it's not intuitive how it works, but:

Cooldown reduction (CDR) decreases base cooldown of the ability.
Cast speed (CS) makes two things happen: it increases cast animation speed (making cast delay shorter - including charged spells), but it also makes spell cooldown timer run faster.

Meaning: both stats decrease spell cooldowns, and their effects stack multiplicatively.

To visualise this:

If you look at the ring arund skill icons, you can see your skill coooldown ticking down. Think of it as a little clock. After you cast an ability, you have to wait for the hand of the clock to make one full revolution.

CDR gives your clock hand a head start - with 50% CDR it'll start ticking at 6 instead of at 12. Your 20s meteor skips first 10s of it's cooldown, effectivaly having 10s CD.

Meanwhile, CS makes the clock hand move faster. With 150% CS your spells will advance their cooldowns by 1,5s for every 1s passed realtime, effectively making the cooldown 1/CS = 1/1,5 = 2/3 ~= 66% of its original, or 34% reduced. Your meteor will effectively have ~13,33s cooldown.

WIth both, stacking multiplicatively, it totals to 0,5 * 0,66 = 33% of original cooldown, or 67% reduction, ie. ~6,66s meteor cooldown. Plus whatever long the cast animation is.

If you want to math it (ignoring animation time):
Spell cooldown multipiler = (1-CDR)/CS * 100%

Generalizing, CDR is slightly better at increasing spell uptime (excluding charged skills), as CS is subject to dimnishing returns, but CS has double the values on item enchants and it makes cast animation shorter too, so it typically comes pretty close in value. And spammy builds want both.

[jp1477]

div.ide původně napsal:

Cooldown reduction (CDR) decreases base cooldown of the ability.
Cast speed (CS) makes two things happen: it increases cast animation speed (making cast delay shorter - including charged spells), but it also makes spell cooldown timer run faster.

Meaning: both stats decrease spell cooldowns, and their effects stack multiplicatively.

Thanks for sharing more details about how this works! That's very helpful info.