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Every unit has unique cast animations for each their spell. The cast animation of a spell starts playing 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. This animations are not bound to spells, but to the ability slots of each unit and hero. The length of the animations vary for each spell as each of them are unique, 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 takes a certain time 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 immediatly, 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 immediatly, but continues playing. For most spells, the unit still stands still during this part of the animation. This is commonly known as cast backswing.

Cast point
All spells require the casting unit to spend a certain amount 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, the spell takes effect. The length of the cast time can vary heavily and is set for each spell individually. But usually, a 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 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 not 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 or a target is chosen for the spell. Some of these instant cast spells do not interfere with any other action the unit take. This means that they can be cast while channeling a spell without interrupting the channeling.

Only spells which require no targeting at all may not interrupt channeling spells upon cast. If a targeted spell (be it unit, ground or area targeted) has an instant cast time, it will interrupt channeling spells. As for spells which require no target, there is no set rule for which of them doesn't interrupt and which does, but most of the time, if the spell ignores backswing animation, it also does not interrupt channeling spells.

All toggle abilities fall under this category. Toggle abilities never use a cast time and cast backswing and do not interrupt channeling spells when toggled.

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 use a cast backswing
 * 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.
 * If it has the "DOTA_ABILITY_BEHAVIOR_IGNORE_CHANNEL" tag, the ability will not interrupt channeling spells upon cast.

Rubick gets a special mention here, as he is the only hero who overrides the cast point of any ability he steals with. Except for a very few spells, 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, this abilities are tagged with "DOTA_ABILITY_BEHAVIOR_NORMAL_WHEN_STOLEN")

Cast backswing
The part of the animation which still plays after a unit reached its spell's cast point is referred as backswing animation. This part of the animation has no impact on the cast spell, so canceling it has no negative effects. Infact, canceling the backswing has benifits for the player, as it allows the unit to perform orders quicker. The player can cancel the backswing by issuing any order to the unit during the backswing. 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.

Since the backswing is the part of animations after reaching the cast point, the length of it depends on how long the animation takes. 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. But if this spell's cast point would get increased to for example 0.6 seconds, the backswing would take 0.4 seconds, since the entire animation still takes 1 second. This leads to various different backswing durations, especially when a unit has multiple spells with differing cast times.

As mentioned earlier. The animations are bound to units, and cast points are bound to spells. As an example, uses the same visual animation (which has a length of 1.1 seconds) for all spells he gains through. This means if he uses for example the ability (which has a cast point of 0.5) from the Harpy Stormcrafter, the cast backswing takes 0.6 seconds. However, the Harpy Stormcrafter animation for its Chain Lightning has a length of 0.97 seconds, so its backswing for it takes 0.47 seconds. Now when steals the Chain Lightning spell from Doom with  and then casts it, the backswing will take 1.07, since Rubick uses no cast time for stolen spells and the animation he uses lasts for 1.07 seconds.

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 are the only 2 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. In most cases, these spells are directly set to ignore the cast backswing. This means, once the spell reached its cast point, the unit will not stand still for the remaining duration of the animation, but will directly continue with the next order if given or queued or will for example start auto-attacking if the player uses the auto-attack function.

Most spells which ignore the backswing have it directly set in the ability, there is no rule for which spells have ignore it and which don't. However, all spells which do not interrupt channeling 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.

All toggle and channel abilities do not use a cast backswing.

Abilities with no backswing
There are 5 ways a spell can have an instant cast point.
 * 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.
 * In some rare cases, the used animation is simply too short to have any backswing animation.

Channeled abilities
Just like with most other spells, a unit starts channeling a spell after having reached the spell's cast point. If the unit is interrupted before reaching the cast point, the spell does not start channeling and does not go into cooldown and use mana. Only after having reached the cast point, a channeling spell goes on cooldown and draws the mana. When a unit gets interrupted during the channeling, the channeling stops.

Item abilities
Item abilities are always cast instantly once their hotkey is pressed or a target is chosen. They never have a cast point or cast backswing.Also, just like regular instant castable abilities, some items which do not require a target do not interrupt channeling spells upon using.