Hello all, I'm just beginning to learn unity scripting. I'm trying to implement them as I learn some very basic functions along the way.

This link from unity taught me the basics of OnCollisionEnter() - which, as far as I understand, executes some piece of code whenever it detects collisions with a gameobject (there they named it as prop_powerCube).

Now I tried to implement it in C# and I had something like:

using UnityEngine;
using System.Collections;

public class Mine : MonoBehaviour {

	// Use this for initialization
	void Start () { 
		int health=10;
	
	}
	
	// Update is called once per frame
	void Update () {
		

//public class DestroyCubes : MonoBehaviour
{
     OnCollisionEnter (Collision col)
    {
        if(col.gameObject.name == "Sphere")
        {
            //Destroy(col.gameObject); 
            health-=5;
        }
    }
}
   Debug.Log("Health=", health);
    }
	
	

In short, it would detect collisions with 'Sphere' and decrease the health of the player by 5. The problem I understand is with "col".

It is a variable of type Collison. But how do I explicitly declare it in this case?

MY AIM: WHENEVER MY PLAYER COLLIDES WITH A SPHERE, HIS HEALTH DECREASES BY 5 UNITS.

Please guide me where am I missing it...

OK. The first thing you must learn is the difference between a "member variable" and a "local variable".

Your "health" variable is currently local to your Start method. That means that no other method can actually access it.

In order for your health variable to be used by all of the methods of your class, you need to declare it as a member variable:

public class Mine : MonoBehaviour
{
    int health;  // this is a member variable

    void Start()
    {
        health = 10; // this sets the member variable.  notice the "int" part is removed because I don't want to declare a different variable here.
    }

The second thing is that for MonoBehaviours that you attach to scene objects or prefabs, Unity only wants you to put one behavior in a single file (this is because Unity internally identifies component types using a unique ID, not the class names). So if you want that DestroyCubes class, you'll have to put it in a DestroyCubes.cs file.

The third problem is that you cannot perform Debug.Log outside of a function like you're doing in your post.

Thanks for the help. I'm having some real trouble with scripts. I don't know why, but what I did as an experiment was put a cube and then whenever I collide with the cube, I'd like to display a message..

I wrote this code, applied it to my player character, and yet on collision with the cube nothing happens :(

function OnCollisionEnter(theCollision : Collision){
 if(theCollision.gameObject.name == "Cube"){
  Debug.Log("I hit it");
 }else {
  Debug.Log("Hit the wall");
 }
}

Things to check:

- Make sure at least one object has a Rigidbody/Rigidbody2D.
- Make sure you aren't mixing 2D and 3D components.
- If you are using 2D components instead of 3D components, change to "OnCollisionEnter2D" and "Collision2D" in your function (this caught me off guard for a while myself).

Somehow the Debug.Log function has stopped working, it seems.

I deleted my entire scene, created a very elementary plane and placed a cube (A 3D RIGID BODY) on top of it.

Then I applied the following script on the cube:

using UnityEngine;
using System.Collections;

public class debug : MonoBehaviour {

	void Example() {
        Debug.Log("Hello", gameObject);
       
    }
} 

I hoped to see a 'Hello Cube' on my console screen. Well nothing really happened.

I have checked clicking the three buttons on the top right of the console screen - up to no avail.

On another note: Is there a 'beginner' way to print things right on the game window? Like, if you collide with an object a pop-up will display something like: "Game over" etc.

Perhaps then, I can do away with this debug.log not working, this has left me quite frustrated after trying to sort it out for almost a couple of hours by now..

In your most recent post, the reason why your Debug.Log isn't working is probably because nothing actually calls your Example function.

Unity automatically calls certain functions, but they have to be named specific things:

- Awake is called when your component is being created.
- Start is called for active components after all other components have had their Awake function called.
- Update is called once per frame per active component.
- OnDestroy is called when a component is being destroyed.

Other ones are listed here, in the "messages" section: http://docs.unity3d.com/Documentation/ScriptReference/MonoBehaviour.html

In addition to those functions, you can make your own functions, but Unity won't call them automatically - you will have to call them yourself (which eventually has to be traced back to one of the methods that Unity calls).



For your second question, Unity's built-in way to draw text and stuff to the screen is to use the "OnGUI" method (that's one of the ones listed in the link above).

The basic process of using OnGUI is:

- Make a method called 'void OnGUI()' in your class.
- Inside that method, call functions such as http://docs.unity3d.com/Documentation/ScriptReference/GUI.Label.html to display labels, buttons, etc.

Most of the useful methods are in these two classes:

http://docs.unity3d.com/Documentation/ScriptReference/GUI.html
http://docs.unity3d.com/Documentation/ScriptReference/GUILayout.html


For more advanced games, I recommend not using Unity's current GUI system - it is not flexible enough. This may be changed in future versions of Unity, but for now, I prefer the third-party "NGUI" library instead. But for simple things, Unity's built-in GUI system works fine and requires writing very little code.

Thanks for all of this.

Just a request: can you kindly give me the full code of the C# file to simply output a message via Debug.Log once my player character collides with a cube in 3D? One such instance of the full code will be of great help. Thanks..

using UnityEngine;

public class Example : MonoBehaviour
{
    void OnCollisionEnter(Collision collision)
    {
        Debug.Log("3D Collision with another object named: "+collision.gameObject.name);
    }
}

Then make sure you attach that component to your player object, and make sure that object also has a collider and rigidbody, and you should be set.

If you still don't see a log message, you might have accidentally disabled log messages in the console window. There are some toggle buttons in the upper right corner of the console log window which enable and disable Debug.Log, Debug.LogWarning and Debug.LogError, respectively.

Thanks a ton. It's working almost the way I want it to. Added a rigidbody component to the cube and suddenly it began to fall through the terrain, so searched in google and applied a mesh collider with the 'convex' option ticked, and the cube stayed on the terrain.

Just a small tweak, the game starts with printing the statement: "3D Collision with another object named: Terrain" even tough the y-coordinate of both the player and the terrain are the same. PRoblem is when I collide with the cube, it says nothing.... So I changed the code to

void OnCollisionEnter(Collision collision)
	
		{ if (collision.gameObject.name=="Cube")
		{
        Debug.Log("3D Collision with another object named: "+collision.gameObject.name);
		}
		}
	

Even this does not output anything upon collision with the cube..

I also tried experimenting with the Collision Detection options - but to no avail

Somehow the cube is not detecting collision, even though I can't directly pass through the cube.

Attached is a screenshot of my Unity Window with the Cube selected..

[attachment=20560:Untitled.jpg]