Creating a key and door

In this step, we will create the finish point, which is the door in this case. We will also create a Trigger Collider, which makes it so that the player can't end the game if he/she didn't collect our item; of course it's the key to our door.

Prepare for Lift Off

Let's prepare and make sure that we have all the graphics that we need; go to the Graphics folder in the Project window, and make sure in our subfolder Level, we have doorClose.png, doorOpen.png, and key.png. Let's get start.

Engage Thrusters

Here, we will create the object's Key and Door. Let's do this as follows:

  1. Let's create the new material for our key, so go to Assets | Create | Material, name it M_Key, and set the following:
    • Shader: Transparent | Cutout | Specular
    • Main Color: R: 255, G: 166, B: 0, A: 255
    • Specular Color: R: 236, G: 224, B: 26, A: 0
    • Shininess: Drag the dragger almost to the right side
    • Base (RGB) TransGloss (A)
    • Drag-and-drop our key.png in the Graphics/Level to the texture thumbnail in the material inspector:
    Engage Thrusters
  2. Next, we create another material for our door; go to Assets | Create | Material, name it M_Door, and set the following:
    • Shader: Diffuse
    • Main Color: R: 219, G: 255, B: 255, A: 255
    • Base (RGB)
    • Drag-and-drop our doorClose.png in the Graphics/Level to the texture thumbnail in the material inspector
  3. Before we create our mesh object, we have to create a new Tag for our Door and Key, so go to Edit | Project Settings | Tags.
  4. Under the Element 3 type Door, and under Element 4 type Key. Now, we will create a key object by using a plane in Unity; it's very similar to our Player. So, go to the Plane prefab object in the FBX folder and drag it into the Hierarchy view.
  5. In the Hierarchy view, right-click on the Plane prefab object, and choose Rename to change the name to Key.
  6. Next, right-click on the Animation component in the Inspector view and choose the Remove Component option to remove it. We will see the pop-up window, so just click on the Continue button similar to how we did for our Player object.
  7. Click on this object and go to its Inspector view, and set the following:
    • Tag: Key
    • Position: x: 21, y: 7.5, z: 0
    • Rotation: x: 0, y: 180, z: 0
    • Scale: x: 2.75, y: 2.75, z: 2.75
  8. Assign our M_Key to this material. Then add the Box Collider to the Key as we did for our Player; go to Component | Physics | Box Collider set Size: x: 1, y: 1, z: 1 and Center: x: 0, y: 0, z: 0, and toggle Is Trigger to true.
  9. Copy the Key by pressing Command + D or Control + D to create the Door object. Then, we name it Door, assign material M_Door to it, and set the following:
    • Tag: Door
    • Position: x: 19.5, y: 16, z: 0
    • Rotation: x: 0, y: 180, z: 0
    • Scale: x: 7.5, y: 7.5, z: 1
  10. We have finished creating our Door and Key. Next, we will go back to our code and add some scripting to make our Door and Key work. Double-click our CharacterController_2D.js, and add these parameters to it:
    public var doorOpenTexture : Texture2D;
public var doorCloseTexture : Texture2D;
private var b_hasKey : boolean;
  11. Then, we add these lines of code to the Start() function:
       //Start with no Key
  b_hasKey = false;

    This will set the character to start without a key.

  12. Next, we add the OnTriggerEnter() function to our code; this function will check if our character hit Key or Door:
    public function OnTriggerEnter (hit : Collider) : IEnumerator {
  if (hit.collider.tag == "Key") {
    if (!b_hasKey) {
      //We hit our Key
      b_hasKey = true;
      Destroy (hit.gameObject);
    }
  }
  
  if (hit.collider.tag == "Door") {
    if (b_hasKey) {
      //If we had Key and hit door the door will open
      hit.gameObject.renderer.material.mainTexture = doorOpenTexture;
      //wait for 1 second and destroy our character
      yieldWaitForSeconds(1);
      Destroy (gameObject);
      //We close the door
      hit.gameObject.renderer.material.mainTexture = doorCloseTexture;
    }
  }
}

    In this function, we are checking if our character hit the key or door by checking their tag. When the player hits the key, the key will destroy itself and we set our character to have a key by setting b_hasKey = true. Also, when we hit the door, we are checking if our character has the key or not. If the character has the key, it will change the door texture to doorOpen texture. Then, we wait for one second to remove our character and we change the door texture back to doorClose texture to close the door.

  13. Before we are done, we need to add doorOpen.png and doorClose.png to the Player. Go back to Unity, and click on the Player; in the Inspector view now, we will see two new parameters, Door Open Texture and Door Close Texture; drag-and-drop doorOpen.png to Door Open Texture and doorClose.png to Door Close Texture. Now we are done.

Click play and try out your game, collecting the key and going to the door. Behold the door opening and closing!

Objective Complete - Mini Debriefing

We just created a key and door object, and placed them at our level. We also created the function that will trigger when the character hits the key and door objects. Then, we changed the texture of our door object when our character had a key object and hit the door. Lastly, we waited for one second to remove our character from the scene and changed the door texture back to closed state by using yield and Destroy.

Classified Intel

We can pause or wait for the next action by using coroutines.

Coroutines

In our script, we need to wait for a second between opening the door and ending the game. We could do this by looping or performing some other task for a second, but that would stop the animations, the sound, and everything else. We get around this by using the yield command; this tells Unity to stop running our function and come back later (in our game, 1 second later as we call yield WaitForSecond(1)). By using the yield command our function becomes Coroutines and now it must return IEnumerator (Unity needs this so that it can tell when to start our function again). This means Coroutines can't return a value like a normal function. We can change most functions in our MonoBehaviours script into Coroutines, apart from the ones which already run in every frame, such as Update(), FixedUpdate(), OnGUI(), and so on. We can get more information about coroutines from the following Unity script reference:

http://unity3d.com/support/documentation/ScriptReference/Coroutine.html.

Next, we will talk about the return type. Sometimes, when we use JavaScript, we don't really care about what type to return or what type of parameters we will pass to the function, because it is really convenient to type only var myParams = 0 or function DoSomething(var). This isn't a bad thing to do, but if we are working with a team of people, it is very important to have code that is readable for others. So, it is better to have this habit. It also makes the code run faster, since it doesn't have to go and do type lookups. On the other hand, if we use C#, we will be forced by the language itself to type the return type of this function or the type of this parameter. So, it's a good thing to know because you will be able to read C# code easily if you have to and it is readable for everyone, even the person using C#.

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