Unity AI Programming Essentials: Use Unity3D, a popular game development ecosystem, to add realistic AI to your games quickly and effortlessly

Create a new 3D scene and import the Quick Path AI from the Asset Store.

Next, set up some cubes, planes, or other objects as your terrain, and then place all of these game objects into an empty game object. Name this game object Terrain.

Next, on the Inspector panel, add a component, QuickPath | Grid. Immediately, you should see a series of blue lines that show up on the cubes. These indicate all the points where a character can move in the AI.

Now, we need a character to move around the scene. Create a sphere, or any object, and name it NPC.

Then, we'll add a Component, QuickPath | AI | Follow Mouse Object.

Now, when you run the scene, assuming it is lit up and has the camera pointing where you want it to, you'll see NPC on Terrain.

Click somewhere on the Terrain object, and watch the NPC object move to that point.

Although we might say that the pathfinding in this is clearly working, we should also add an obstacle to the scene: something that shouldn't be stepped on. To do this, add another cube somewhere. Go to the Inspector panel for the obstacle and tag it with Obstacle by selecting that tag from the drop-down, or if it is not an option select Add Tag... and add Obstacle to the tag list.

Next, in the Terrain game object, in the Grid component, expand Disallowed Tags, increase the size to 1 and enter Obstacle for the new element.

Next, click on the Bake button at the top of the Grid component. Now you will see that the grid markers skipped the cube as an option. If you want to test more, click somewhere else on the Terrain object and watch the NPC object move to the clicked point avoiding the obstacle.

Add a plane or another ground type. Then add several obstacle objects, such as cubes. Make sure that each of the objects we just created are marked static at the top of the Inspector, or the NavMesh won't identify them later on. The scene should look like this:

Next, find the Window menu and select Navigation. At the bottom of the Navigation tab, click on the Bake command. You have now generated a simple navigation mesh for your characters to navigate. It will highlight the areas that NavMesh AIs can walk, as seen here:

Let's add a player who can move around the world now. Add a capsule and name it Player. Fortunately, the demo contains a simple script for controlling a player who you can find (and add) by navigating to Add Component | Scripts | Simple Player Control. Now, this doesn't move the object around on its own; instead it drives a Character Controller object.

When adding the component, just start typing Character Controller in the search box, and it will show you all the similar component names. Add Character Controller. Now, the player should be controllable. You will probably need to increase the speed to 1 to detect the player movement.

Next, we'll add an enemy in the same way, with Capsule. The enemy needs a component called Nav Mesh Agent, which is a component capable of using a NavMesh to move around, so add it. Now, the game object has the ability to walk around, but it has nowhere to go. To get it moving, we need to add the enemy AI agent.

Next, we get to the AI for the enemy agent. In React, a behavior tree is called a Reactable. To add a reactor, we start the Project explorer, in a folder of our choice, by navigating to Create | Reactable.

Once created, rename it to EnemyMovement. In the Inspector, it has a list of behaviors for it. We'll need to add a script, which can be found in the book's contents: \Scripts\React AI\FollowThePlayer.cs. Without going in-depth in the code, let me explain the following key points:

This script needs to be added to the Inspector for the EnemyMovement asset, and also to the Enemy game object.

Once the script is attached to the enemy, the Inspector will reveal that it has a target. Drag the player from the Hierarchy panel into the player attribute on the Inspector panel.

Finally, we have the behavior tree to set up. In the Project panel, right-click on the EnemyMovement asset, and click on Edit Reactable. A behavior tree pops up an editor, which is how we train our AI.

To create our map, add a plane. Then, add a couple of objects to act as obstacles. It is best if they create a U or V shape to potentially trap the player:

Next, drag the predefined character found in Project | Standard Assets | Character Controllers | Sources | Prototype Character | "constructor" into the scene. From the scene depicted in the preceding screenshot, I recommend placing him (the character) on the back left-hand side of the plane.

Next, we need a route. Although there is more than one waypoint system in RAIN, I found that the route will be the fastest for this demo. In the RAIN menu, click on Create Waypoint Route. Name it's game object GreenPath. We will need to call this later, so we want simple, easy names to remember.

In the Inspector panel for GreenPath, click on the Add (Ctrl W) button. This adds a waypoint. In fact, we need to add three. Place the first one on the inside of the V, the second on the tip of the V, and the last on the far edge of the plane, as shown in the following screenshot:

Just as in React AI and Unity NavMesh, we need a navigation mesh for this as well. We clearly defined the route, but as you can see, the path is blocked. In the RAIN menu, click on Create Navigation Mesh. Align and stretch it so that it surrounds the area where you want the paths to be determined.

The Inspector panel for the NavMesh has a property called Ignored Tags. Add Player to this list. (You might need to make sure that the player object actually has that tag selected as well.) Otherwise, the NavMesh will not generate where the player stands, and will prevent its ability to find a path. Then click on Generate Navigation Mesh at the bottom of the Inspector panel. The result should look like this:

Next, we need to add an AI to control the character. Select the player object in the Hierarchy panel, and from the RAIN menu, click on Create AI.

Next, select the middle button of the character running in the AI Inspector panel, then click on the Add Existing Animations button at the bottom. This will add all the player's animations: idle, walk, jump, pose, and run. You can refer to the following screenshot:

Next, we need to add a behavior tree. Behavior trees are a way to define decisions and actions for AI characters. We will discuss them in more detail in Chapter 3, Behavior Trees. For now, add one by clicking on the head/brain icon in the Inspector panel and then click on the Open Behaviour Editor button. On the right-hand side is a behavior tree drop-down selector, so click on it and choose Create New Behaviour Tree.

Name it FollowGreenRoad. It will already have one element, SEQ (Sequence), under the root BT (behavior tree) node. Sequence it means that it will run any child nodes in order. Right-click on the SEQ node and navigate to Switch To | Parallel, which means that it will run all its child nodes simultaneously.

Let's add the child nodes and then set them up. Right-click on the PAR node, then navigate to Create | Actions | Animations. Right-click on PAR again and navigate to Create | Actions | Choose Patrol Waypoints. Then right-click on the new WAY node and navigate to Create | Actions | Move.

Because the decision is to run things in parallel, it will animate the character and follow the waypoints at the same time.

Click on the green animate node, and set its animation state to walk. It is case sensitive, but you can select which animation the character should use.

Next, select the WAY node. Here, you need to set Waypoint Route to use. This was the navigation route we created earlier with the three waypoints. We called it GreenPath.

For the loop type, we'll make it One Way so that the character only travels to the end and stops there. Also, change the name of the loop to Follow Green Path. This shows up next to the WAY node, and helps explain what is happening.

Finally, set the Move Target Variable to NextWayPoint. This is a variable that we are setting with the next waypoint in the path. When it is reached, the patrol route will set the variable to the next location in the path. We use this in the Move node.

Select the move node, and in the properties, set the Move Target to NextWayPoint, the variable that is being set by the patrol route we just configured. And set the Move Speed to a number, such as 3. This is how fast the character will move.

Now that we have created the behavior tree, we need to set the Character AI to use it. Select the AI object under the player object in the Hierarchy panel. On the Mind icon, for the Behavior Tree Asset, set it to FollowGreenRoad. This can be found by navigating to Project | AI | Behavior Trees, or from the selector in the Inspector panel, choose the Assets tab, and it should be right on top.