10 - Rotating Turret
In this lesson, you will create a simple Turret that rotates to face enemies that are nearby.
Challenge: Create a Turret Prefab
- Create a new Prefab to represent a turret
- Add a model to the Prefab (I will be using the
weapon-ballistamodel but you may use any model) - Create a new
TurretTargetMonoBehaviour Script - Attach the
TurretTargetcomponent to your Turret Prefab - Add a Turret to your Scene
- Adjust the model's, Y position to be slightly above your ground tile. The grass / snow tiles are 0.2 units thick.
- Add a few instances of your Turret Prefab to your scene
If all went well, your Scene should look similar to this:
Area of Engagement
Before your turret can rotate to face an enemy, it must be able to detect enemies that are within range. To do this, you will define an Area of Engagement using a collider that will track enemies that are within range.
- Add a Sphere to your Turret
- Rename the Sphere (I recommend "Area of Engagement")
You can change the range of the Area of Engagement by adjusting the scale
- Adjust the range of the Area of Engagement by adjusting the scale.
- The scale represents the diameter of the Sphere. A size of 3 is large enough to hit all 8 surrounding tiles. Feel free to
- Note: You can click the constraint button to change all 3 axes at the same time
- Find the Sphere Collider component in the Inspector
- Enable Is Trigger
- In Unity's physics system, trigger colliders allow other objects to pass through them.
Transparent Material
Currently, your Area of Engagement is being drawn as a hideous sphere in both the Scene and Game views.
You can create a transparent Material that will allow your player to visualize the area of engagement while not preventing them from seeing enemies that pass through.
- Create a Materials folder in your Assets
- Right click in the Project View
- Select Create > Rendering > Material
- Name the Material (I recommend "Area of Effect Material")
- Select the Material
- Drag the Material on to your Area of Effect in the Prefab Editor
- This will change the Material in the Mesh Renderer component. Alternatively, you could set it directly in the Inspector
- Select the Area of Effect Material in the Project View
- In the Inspector, set Surface Type to Transparent
- Click on the color to the right of Base Map to change the color of the Material
- Be sure to adjust the Alpha value so the material is transparent
Adjusting the Metallic Map and Smoothness property of the Surface Input changes how reflective the material appears. To make the material have no "shine" to it, set both of these values to 0.
- Set the Metallic Map and Smoothness properties to 0
Modifying the Y Scale
You may have noticed that it is quite difficult to determine which tiles are within the area of engagement in the isometric game view, especially the tiles that are on the far side of the turret.
To help with this, you can modify the Y scale of the Area of Engagement. This will make it more obvious where the edge of the collider is located.
- In the Prefab Editor, select your Area of Engagement
- Set the Y Scale to 1
- You may need to disable your scale constraint toggle
Note: The Sphere Collider uses the largest of the 3 scales to determine its size. The Colliders are shown in the Scene View using green lines. You can verify the size of your Sphere Collider by clicking on the Area of Engagement in the Hierarchy.
Enemy Collider
Before you can detect if an enemy has entered an Area of Engagement, you must first add a Collider to your Enemy Prefab.
Challenge: Add a Capsule Collider to Your Enemy Prefab
- Open your Enemy Prefab
- Add a Capsule Collider component to it
- Make the Collider a Trigger
- Adjust the Capsule Collider's size to roughly the size of your enemy
- You can use the Edit Collider button on the Capsule Collider component to edit this in the Prefab View
When you're finished, your Enemy Prefab should look similar to the image below:
Add a Rigidbody to Area of Effect
You can use the Collider.OnTriggerEnter(Collider) method to detect when a Collider has entered a Trigger Collider. However, for the physics system to detect this, at least one of the Game Objects must be part of a Rigidbody. In this case, you can add a Rigidbody to the Area of Effect that is Kinematic.
- Open your Turret Prefab
- Select the Area of Engagement from the Hierarchy
- In the Inspector, add a Rigidbody component
- Set the Rigidbody to be Kinematic
- A Rigidbody that is Kinematic is unaffected by simulated physics forces.
AreaOfEngagement MonoBehaviour
At this point, everything is ready for you to detect when an Enemy has entered the Area of Engagement using the OnTriggerEnter(Collider) method.
- Create an
AreaOfEngagementMonoBehaviour Script - In the Turret Prefab, add the component to your Area of Engagement object
OnTriggerEnter(Collider)
- Read the Friendly Manual: Unity - Scripting API: Collider.OnTriggerEnter(Collider)
- Add a
void OnTriggerEnter(Collider)to yourAreaOfEngagementMonoBehaviour - Add a
Debug.Log()to verify that the trigger is working
- Enter Play Mode and open the Console to verify the Trigger is working
If all went well, your console should look similar to the video below
Tracking Enemies
You can use a List<Transform> to track the potential targets.
- Add a
List<Transform> Targetsproperty to your Area of Engagement- If you Serialize this property, you can view it in the Inspector
- In
OnTriggerEnter, add the entering collider to theTargets
- Enter Play Mode and verify that the Targets are being added to your Area of Engagement
If all went well, you should see the Enemy's collider being added to the Targets list when they enter the trigger collider.
Challenge: OnTriggerExit
Next, you will want to make it such that your Area of Engagement removes Enemies as they exit the trigger collider.
- Read the Friendly Manual: Unity - Scripting API: Collider.OnTriggerExit(Collider)
- Implement
OnTriggerExit(Collider)such that the collider's transform is removed when the enemy exits the Area of Engagement.
If all went well, you should see the collider's being removed from the Targets list in the inspector. You may find it useful to increase the size of the Area of Engagement to test this.
TurretTarget MonoBehaviour
With your Area of Engagement script tracking the enemies that are near the Turret you can now implement the TurretTarget MonoBehaviour to rotate to face one an Enemy in the Targets list
- Add a
AreaOfEngagement AreaOfEngagementproperty - Add a
GameObject Modelproperty - Serialize both properties and set them in the Inspector
- Set both properties in the Inspector to reference the model of the Turret Prefab
Challenge: Rotate the Model to Face the first Target
- In
Update, ifAreaOfEngagement.Targetsis not empty- Call
Model.transform.LookAtto rotate the model to face the first Enemy in AoE.Targets
- Call
If all went well, you should see your Turrets rotating to face enemies as they pass by:
What's Next
With your turrets successfully tracking the enemies as they pass by, it is time to create a Projectile that can be fired at the enemies to destroy them.