08 - Waypoint Traveler

With your Waypoints set up, it is time to update your Enemy to follow your Waypoints.

High level design idea

Enemy has a Target Waypoint that they move toward
When the Enemy reaches their Target they query the Waypoint for the Next Waypoint and update their Target Waypoint
If there is no Next, the Enemy stops moving

Vector3.MoveTowards

You can utilize Unity's built in method Vector3.MoveTowards to do most of the heavy lifting for the Enemy's movement.

Read the Friendly Manual: Unity - Scripting API: Vector3.MoveTowards
Add a Target Waypoint property to your Enemy Movement script
Be sure to Serialize the property so it can be accessed in the Inspector

In the Update method, call Vector3.MoveTowards to update the Enemy's position
- Note: Use Time.deltaTime*Speed as the maxDistanceDelta

In the Inspector, set the enemy's Target Waypoint to your first waypoint

Enter Play Mode and verify that your Enemy moves to the specified Waypoint

While you are in Play Mode you can even switch the Waypoint to test that when the Waypoint is changed, the Enemy will move to the new Target

Changing Waypoints

You need a way to determine how close the Enemy is to their Target Waypoint. This can be done using Vector3.Distance.

Read the Friendly Manual: Unity - Scripting API: Vector3.Distance
After the Enemy has moved, calculate their distance from the Target Waypoint
If the distance is sufficiently close to 0, the Enemy's Target updates to the next Waypoint

Enter Play Mode to verify your Enemy moves between each Waypoint

You may have noticed the odd expressions distance <= 0 and might be asking yourself, "Why are we checking if the distance is less than or equal to 0 and not just equal to 0?". Great question! I'm so glad you asked! As you may already be aware, floating point numbers are approximated values, that is they should not be used for precise calculations (See: Is floating-point math broken? - Stack Overflowfor greater detail).

In our case, it is possible that we may not actually get a value of 0, and instead we want to check if the distance is sufficiently close to 0. In Unity, this often done using Mathf.Epsilon (which happens to be approximately 0.00001f).

Update your code to use Mathf.Epsilon in place of 0

Challenge: Fix the NullReferenceException

You may have noticed, when your Enemy reaches the final Waypoint an error message appears in the Unity Console.

Fix the NullReferenceException

The Start() Method

Currently, your Enemy begins its journey by moving to your first Waypoint. You may have already moved the Enemy to start at that position when you enter Play Mode. However, it is not guaranteed. One way to fix this, is to use the Start() method to move the Enemy to their first Target before the first game frame.

Update your Start() method to set the Enemy's initial position to the Target's position.

Adjusting the Model's Y Position

If you placed your Waypoints such that their Y position is at 0 (level with your grid), you might have noticed that when your Enemy's model is slightly below the ground. You might be tempted to move your Waypoint's such that they are slightly above the ground. This would solve this issue. However, you can instead adjust your Enemy Prefab to such that the inner model is slightly elevated relative to the parent object.

Open the Enemy Prefab
Select the model in the Hierarchy
Set the Y position to (0.101)
- The dirt tile is 0.1 units thick. Setting the Y position to be slightly above will make your enemy model appear on top of the tile.

Challenge: Rotate the Enemy to Face their Target Waypoint

Unity provides a method called Transform.LookAt that can be used to make a Game Object rotate toward another Game Object. You can utilize this, to make your Enemy face their Target Waypoint.

Read the Friendly Manual: Unity - Scripting API: Transform.LookAt
Remove the Enemy Rotation component from your Enemy
When the Enemy changes Targets, call the Transform.LookAt method to rotate the Enemy to face the next Waypoint
Fix any NullReferenceExceptions that occur

When you have successfully completed this challenge, your Enemy should look similar to the one in the video below.

What's Next

With your Enemy's moving, it is time to create an Enemy Spawner that will generate additional enemies during game play.