Cast Animation

Every unit has unique cast animations for each their spells. The cast animation of a spell is enacted as soon as a target for the spell is chosen, if it requires one, or its hotkey is pressed, if it does not require a target. These animations are not bound to specific spells, but rather to the ability slots of each unit and hero. The length of the animations vary for each spell as each of them are unique and made for the spell the unit usually has in the slot the animation is bound to. Although "cast animation" only sounds like a visual part of the game, it does have a mechanical influence on the gameplay.

Every spell has a certain time frame the casting unit has to go through in order to successfully apply the effects of the spell. This time is commonly known as cast point or cast time. This cast time is set for each spell individually, and has nothing directly to do with the visual animation of the spells. However, since the animation starts playing immediately, it indicates the cast point of spells.

In almost every case, the length of cast animations exceed the cast point of spells. Upon reaching the cast point, the animation does not stop immediately, but continues playing. For most spells, the unit still stands still during this part of the animation, and is unable to act until the animation has completed. This is commonly known as cast backswing.

Cast point
All spells require the casting unit to spend a certain amount of time before the spell's effects are applied. This time window is known as cast point or cast time. Only once the unit reaches this point does the spell take effect. The length of the cast time can vary heavily and is set for each spell individually. Usually, a specific unit's spells share the same cast point.

An ability only applies its effects, goes on cooldown and expends mana when the casting unit successfully reaches the cast point of the spell. This means when the unit gets interrupted by disables or their own actions before reaching the cast point of the spell, the cast gets canceled, the spell's effects do not get applied, it won't go into cooldown and won't draw mana. The player also can manually stop the spell cast by issuing a stop or halt command. When the spell cast gets interrupted during the cast time, the visual cast animation ends as well.

Instant cast
Quite a few spells have an instant cast time, meaning their effects are instantly applied as soon as the spell hotkey is pressed (if they are not targeted) or a target is chosen for the spell (if they are). Spells which require no targeting at all may not interrupt channelling spells upon cast. If a spell is targeted (be it unit, ground or area) it will interrupt channelling spells, even if its cast point is instant. As for spells which require no target, there is no set rule for which of them don't interrupt and which do, but most of the time, if a spell does not have a backswing, it also does not interrupt channelling spells.

All toggle abilities fall under this category. Toggle abilities have neither a cast point nor a backswing, and as such never interrupt a channel. This applies to most toggled Items too, but some such as Power Treads are not considered a toggle and as such can interrupt.

Abilities with instant cast

 * There are 3 ways a spell can have an instant cast point.
 * Its cast point is simply set to 0, in which case it will still use a cast backswing.
 * It has the "DOTA_ABILITY_BEHAVIOR_IMMEDIATE" tag, which causes the spell to neither possess a cast point, nor a cast backswing.
 * It has the "DOTA_ABILITY_BEHAVIOR_TOGGLE" tag, which turns the ability toggle-able, means it also neither uses cast point nor backswing.
 * If it has the "DOTA_ABILITY_BEHAVIOR_IGNORE_CHANNEL" tag, the ability simply will not interrupt channelling spells upon cast.

Rubick gets a special mention here, as he is the is capable of stealing abilities and altering their cast point with. With very few exceptions, all spells he steals use a cast point of 0 seconds.

The following spells use the original cast point, instead of the 0 second cast point override (in the game files, these abilities are tagged with "DOTA_ABILITY_BEHAVIOR_NORMAL_WHEN_STOLEN")

Cast backswing
The part of the animation which occurs after cast point has been reached is called backswing animation, and during it the unit is unable to attack or use abilities. This part of the animation is purely a liability; it has no effects besides temporarily impeding the unit, and as such it is beneficial to cancel a long backswing animation, which will allow the unit to execute other commands sooner. The player can cancel the backswing by ordering the unit to move (ideally forward) or simply by using an item or casting another spell. Disables, including silence, will cancel it as well. However, queued orders do not cancel it. If orders are queued, the next order will be executed after the backswing finishes.

Backswing is individual to units and their abilities, and is not necessarily the same length even for spells with the same total animation time. For example if the entire animation of a spell takes 1 second, and the spell's cast point is at 0.3, the backswing will take 0.7 seconds. However, a spell animation of the same length with a 0.6 cast point would only have 0.4 backswing. Some units (and/or specific abilities) have long backswing animations, and it is on these units that cancellation of backswing will be most beneficial. Cancelling a short backswing is difficult, and generally achieves minimal difference in outcome, so it is not generally done.

As mentioned earlier, animations are bound to unit ability slots, whereas cast points are bound to the specific spells. As an example, uses the same visual animation (which has a length of 1.1 seconds) for all spells he gains through, meaning that irrespective of the brevity of the devoured unit's animation, when Doom performs the ability the animation will take 1.1 seconds - his animation time for that slot. This means if he were to use the ability (which has a cast point of 0.5) from the Harpy Stormcrafter, the cast backswing necessarily takes 0.6 seconds, to conform to Doom's 1.1 second total animation, even though when performed by the Harpy itself the ability has a different backswing time. If steals the Chain Lightning spell from Doom with  and then casts it, the animation will become the animation for Rubick's ability slot, and consequently the backswing would be 1.07.

This goes for every animation and ability. But since Ability Draft is the only game mode where abilities can have a different slot or be on different heroes, this only matters in that game mode. In all other game modes, it only matters for Doom and Rubick, since they presently are the only heroes which can acquire spells of other units.

Ignoring backswing
Just like how there are spells with no cast point, there are also many spells with no cast backswing. This means, once the spell reached its cast point, the unit will not pause, but will directly continue with the next order if given or queued.

Most spells which ignore the backswing have it directly set in the ability, there is no rule for which spells ignore it and which don't. However, all spells which do not interrupt channelling spells upon cast will ignore the cast backswing. Some abilities do not directly ignore the backswing animation, but rather leave the unit no other choice than to skip it. These abilities usually force an order on the unit as a part of the spells effect, such as ordering Juggernaut to attack the target or the Spirit Bear's  ordering the bear to stop.

No toggle or channel abilities have a backswing.

Abilities with no backswing
There are 5 ways a spell can have an instant cast backswing.
 * It has the "DOTA_ABILITY_BEHAVIOR_IGNORE_BACKSWING" tag, which causes the spell to ignore the backswing animation. It causes the visual animation to instantly stop once the cast point is reached.
 * It has the "DOTA_ABILITY_BEHAVIOR_IMMEDIATE" tag, which causes the spell to neither use cast point, nor cast backswing.
 * It has the "DOTA_ABILITY_BEHAVIOR_TOGGLE" tag, which turns the ability toggle-able, means it neither uses cast point nor backswing either.
 * Its backswing gets interrupted by forced orders issued by the cast spell, or is a channeling or transforming spell.
 * In some rare cases, the used animation is simply too short to have any backswing animation.

Channelled abilities
Unlike other spells, which go into backswing (if there is one) after reaching cast point, channelled abilities go into a channel after cast point. If the unit is interrupted before reaching the cast point, the spell does not start channelling and does not go into cooldown and use mana. Only after having reached the cast point will a channelled spell go on cooldown and draw mana. If a unit gets interrupted during the channelling, the channelling instantly stops. Channelled abilities necessarily do not have backswings, as the channel must follow the cast point where the backswing otherwise would.

Item abilities
Item active abilities are always cast instantly once their hotkey is pressed or a target is chosen. They have a cast point of 0 and they cannot have backswing.

Just like regular abilities, some item abilities do not interrupt the current spell animation upon using. 1 Toggling these does not interrupt.

2 Also does not interrupt when targeting allies.