I Put a Spell on You

Cast Rate

Casting speed, the duration needed to cast a spell, is class-dependent. It also differs when wearing certain weapons or using special animations (sequences). The Action Flag, which marks the animation frame releasing the spell, is set to quite different moments during the animation, and especially with Amazon class differs amazingly, but is always very late in the process when equipped with different weaponry. This is a reason why Amazons can be interrupted during casting quite easily.
Some Druids' and Sorceress' spells use sequence animation, so they have different casting speeds when using different spells.
Increasing the Casting Rate won't shorten the Delay of some spells, see Cast Delay paragraph on this page.
Necromancer's behaviour while transformed into a Trang Oul Vampire is covered at this topic over at the Phrozen Keep.
Assassin's Trap skills gain no profit by Casting Speed, this is a die-hard rumour.

Items with faster cast rate property are listed at Atair's d2wissen.

indiablo.de presents a FCR Calculator. Unfortunately it doesn't cover all special cases.

In 1.09 Sorceress' Lightning and Chain Lightning weren't subject to casting speed but to attacking speed. This was fixed with 1.10. Iron Wolves' spells always were subject to casting speed.

formular derivation

At first we calculate effective casting speed. It is subject to a 'diminishing returns' formula, so you need more and more of it to achieve smaller and smaller steps onwards.

eFCR = [FCR * 120 / (FCR + 120)]

eFCR: effective Cast Rate FCR: Faster Cast Rate granted by items [ ]: Floor Function

Then we get Casting Speed in frames:

Anim_Dur = {256 * Anim_Length / [v_anim * (100 + eFCR) / 100]} - 1

Anim_Dur: Animation Duration in frames Anim_Length: class-specific base constant, technically called FramesPerDirection v_anim: Animation Velocity, technically called AnimSpeed eFCR: effective Cast Rate from first formula [ ]: Floor Function { }: Ceiling Function

v_anim or AnimSpeed is commonly 256. As an exception the Druid in human shape gets 208, as Werewolf 168 and as Werebear 152. Refer to AnimData.d2 extraction for huge tables, if you like them. You'll find class- and weapon-specific Anim_Length in FramesPerDirection column there, too. This is the reason of some very odd special cases.

eFCR is subject to a hardcoded limit at 75, so more than 200% FCR is useless.

Sequences

Spells marked by SQ in Skills.txt use a special sequence animation. A sequence is a succession of animation bits taken from an existing common animation. As an example, sorceress' SQ animation contains two times the Get Hit animation succession and some pictures in between. Nevertheless the SQ animation is accelerated by FCR, not by FHR.

further readings:

• Do the Fast Cast Breakpoints are the same for all spells?, by Myrdinn
• casting speed and delays
• faster cast rate formula?
• about animations, by Hammerman

see also:

• table of Casting Rates
• extraction of AnimData.d2
• extraction of Skills.txt

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Casting Delay

During the ages and patches blizzard nerfed more and more skills with a Casting Delay.
This should prevent a character from very quickly using very strong skills repeatedly. Unfortunately the mechanism is a bit crude, once a Casting Delay is active every skill subject to that mechanism can't be used by the character.
Casting Rate itself is a completely other kind of peanut, it won't help much. The Casting animation will be accelerated, but the Delay stays the same, so you will gain some frames, but still suffer up to some seconds delay duration. At least you can use another skill earlier which is no subject to Casting Delay.

see also:

• Casting Delays of all skills
• extraction of Skills.txt

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Credits

• Hammerman
• Myrdinn
• nookiestar
• RTB

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