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Lab 2: Collect Them All - Picking Up "Home Made" Objects


The goal of this lab is to create an interactive scene where you can walk around and pick up various “home made” textured objects you have created with Blender 3D.


  1. Install Blender You need to install Blender 3D on your own machine before you start. You get the latest version from the Blender 3D Home Page.
  2. Install Gimp (or similar) It is also good to have an image editing program ready, such as Photoshop or the powerful but free Gimp image editor.
  3. Set Up Unity Folder In Unity it may be a good idea to organize all of your VIEN work inside a dedicated VIEN folder in the Project panel. To do that, right-click on Assets and select Create→Folder and type VIEN as the name. Under the VIEN folder, create three more folders: Scenes, Scripts and Props.


  1. Basic Scene In Unity, start with an empty scene. Add a floor (as a Plane game object) and replace the Main Camera with a FPSController from the Characters Assets Package. Make sure you can walk around your plane. Feel free to embellish this scene with other visuals (e.g. remove the skybox and add fog in Window→Lighting, sky color can be changed in the Camera component of the FPSController→FirstPersonCharacter game object). Save your scene in your “VIEN/Scenes” folder.
  2. Create a Textured Object In Blender, create a new object from scratch with some texturing and save it directly into your Unity project folder under “Assets/VIEN/Props” (the folders shown in the Unity Project panel are all in the same folders on the hard disk). For this step follow the instructions on the Blender Model Export and UV Texturing
  3. Make Object Instance Sense Collision Once you have instanced your new textured object as a GameObject in the scene (you can either drag it into the Hierarchy panel or drop it onto the plane in the Scene view), click on it in the Hierarchy view and in the Inspector panel click on Add Component and use the search box to search for a Sphere Collider. Add this collider component to your game object. In the Sphere Collider check the Is Trigger check box. You have now created an invisible sphere around your object, which generates a trigger event if something collides with it. You can control the radius of this sphere directly from the Radius property in the Inspector panel.
  4. Create a Pickable Behavior You now have to add code to the object to tell it what to do when a collision is detected. In Unity, such behavior code is really just another component that can be added to game objects. We first have to create that component as an Asset, before we can attach it. So, in the Project panel, navigate to your Scripts folder (or create one under VIEN if you haven't already). Right-click inside that folder and select Create→C# Script. Name the new script Pickable, double-click it to open the editor and add the following method to the class that appears:
    	void OnTriggerEnter(Collider col) {
    				if (col.gameObject.tag == "Player") {
    						col.gameObject.SendMessage ("Pickup");
    						Destroy (gameObject);

    Save the code (Ctrl-S) and back in the scene, select your object and in the Inspector press Add Component where you can use the search to find the Pickable script. Add it.

  5. Tag the Player To be able to identify the FPSController game object as the player, you have to give it a named tag. Select this game object in the scene and in the Inspector find the Tag property near the top. Select Player from a drop-down list of available tags. Now it is easy to “ask” this game object whether it's actually the player.
  6. Test Collision Hit Play, you should be able to walk around and when you collide with the object it should get destroyed. However, you will see an error stating that “SendMessage Pickup has no receiver”. This is because your object has sent a message to the player, expecting a method there with a matching name. We will add this method next.
  7. Create Inventory Behavior In the same way you created the new Pickable script, create another C# script in your script folder called Inventory. Edit this script in the following way:
    1. Add a public member variable to hold a sound:
      public AudioClip pickupSound;
    2. Add a method, with the name of the pickup message, to play the sound when called:
      	void Pickup() {
      		AudioSource.PlayClipAtPoint (pickupSound, transform.position);

      Save the code (Ctrl-S) and back in the scene, select your FPSController game object and in the Inspector press Add Component where you can use the search to find the Inventory script. Add it.

  8. Test Inventory Behavior Once you have added the Inventory behavior to your player, you have to associate the pickupSound variable of the Inventory component in the Inspector panel with a sound asset. You can use whatever sound effect you like. You just have to make sure that the sound file is somewhere under the Unity Assets folder so that you can browse to it. You can either fill in the value for the sound file by pressing the little target circle next to the edit box of the Pickup Sound property, or you can drag a sound from the Project panel right into the edit box. After you have provided the sound, you should play the scene and make sure you hear it when the player runs into the object.
  9. Make a Pickable Object Prefab In order to create multiple instances of your object, that now includes a behavior for being picked up, you can turn it into a Prefab. In the Project panel, navigate to your VIEN folder and create a new sub-folder called Prefabs. Open that empty folder. Now drag the working instance of your object in the scene into this Prefabs folder (you are essentially storing the complete configuration of your game object into a template kind of structure that Unity calls a Prefab). Change the name of your new prefab object in the Projects panel into PickableObject or something like that (notice that the name also changes up in the scene). Now you can drag this prefab into your scene as many times as you want to make multple copies of it. If you wish to change any properties in all of them simultaneously, you can select the prefab instead of an object instance and use the Inspector to edit a property that then gets propegated to all instances of that prefab.
  10. Add a Counter to Inventory You should do this on your own. Maintain a state in the Inventory class that knows how many objects have been picked up. Display this number on the screen. To have a class write something onto the GUI, you override the void OnGUI() method of that class (inherited from MonoBehavior. This method gets called whenever the GUI gets updated by Unity. Here is an example of that method being used to write a sample number on the GUI:
    	void OnGUI() {
    		int number = 2;
    		GUI.Label(new Rect(0,0,Screen.width, Screen.height),"Number:"+number.ToString());
  11. Extend your Scene From here you can go wild with making your scene interesting!
/var/www/ailab/WWW/wiki/data/pages/public/t-vien-15-3/lab2_collect_them_all.txt · Last modified: 2015/08/27 17:02 by hannes