Unity3D: When are transition conditions evaluated

Question

I have a very simple game running in Unity, and unfortunately, it is not working as expected. The Context I have the following setup: (source: mazyod.com) From any state, if an integer parameter `direction` is equal to `1`, set animation `player_move_e`. Same goes for `2`, `3`, `4` for the other directions. Once `direction` is set to `0`, the idle animation associated with the direction is played. An important thing to point here is, since I am using the "Any State" block, I must make sure that once the animation state changes to one of the move animation states, I reset `direction` to sentinel value, like `-1`, that keeps the animation state in the current state, and not change states to itself again. The Problem When the player is in the, say, `move_n` state, and I quickly change the direction to the, say, `move_e` (not giving it enough time to transition to idle), the animation state is stuck at the `move_n` :( How can I know if the transition happened, and I am not updating too of…

Accepted Answer

I built a small scene for myself and played around a little bit. I could reproduce your problem and even found a simple solution.

Why it happens

The problem seems to occur when the animator state machine is still in transition to a new state. During that time, new parameter values are ignored but your code is going to change that value again in the next `update()` call. The state machine ignored your new direction and now only sees a value for which it has no transition available, `direction = -1` for example.

The default behavior for transitions is `atomic` which means according to the reference that it cannot be interrupted. However, setting it to false made no difference... It could be a bug and you may want to file a bug report.

Solution

You need to check if the state machine is currently in a transition by checking `IsInTransition(int layer)` like this:

```
void Update()
{
    // update animator (Stupid transition from any state includes current state -_-")
    int heading = CalculateHeading(horizontalInput, verticalInput);

if (heading != previousHeading && !anim.IsInTransition(0))  // you may need to adjust the layer index
    {
        anim.SetInteger("direction", heading);
        previousHeading = heading;
    }
    else
    {
        anim.SetInteger("direction", -heading);
    }
}
```

Another possible solution

I don't know what kind of animations you are using for the different directions, but it may be easier to use one animation and just turn your character around :) This way you have less transitions and states and it may be easier to add more animations later on.