Cast animation/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.

Losing vision of target cancels cast animation.

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.

An ability's cast time is indicated by a green overlay on the ability icon, which swipes over it during the cast time of the ability.

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 channeling spells upon cast. If a spell is targeted (be it a unit, the ground or an area) it will interrupt channeling 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 does not interrupt channeling spells either.

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 are not considered a toggle and as such can interrupt.

Spells which are tagged as "immediate" or "toggle" (tags can be seen below) can also be cast in-between chain-disables (e.g. into, or any disable which uses invulnerability into a periodic area disable like  or ), since these spells have the highest priority of cast order. These spells can also be cast after an Ancient has fallen, during the scoreboard phase.

Abilities with instant cast
There are 3 ways a spell can have an instant cast point: If it has the "DOTA_ABILITY_BEHAVIOR_IGNORE_CHANNEL" tag, the ability simply will not interrupt channeling spells upon cast.
 * 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, meaning it neither uses cast point nor backswing either.

Items with instant cast
Items generally don't have a cast animation. This list contains all item spells that additionally have one of the 'immediate' tags.

Rubick
gets a special mention here, as he is the only hero capable of stealing abilities and altering their cast point with. With very few exceptions, all spells he steals use a maximum cast point of 0.15 seconds.

The following spells use the original cast point, instead of the 0.15 second cast point override (in the game files, these abilities are tagged with "DOTA_ABILITY_BEHAVIOR_NORMAL_WHEN_STOLEN"):

Анимация применения/Время применения 施法动作/施法点