The previous chapter closed by creating a basic coin object from a non-uniformly scaled cylinder primitive. This object was created by selecting GameObject | 3D Object | Cylinder from the application menu. See Figure 2.1. The coin object, as a concept, represents a basic or fundamental unit in our game logic because the player character should be actively searching the level looking for coins to collect before a timer runs out. This means that the coin is more than mere appearance; its purpose in the game is not simply eye candy, but is functional. It makes an immense difference to the game outcome whether the coin is collected by the player or not. Therefore, the coin object, as it stands, is lacking in two important respects. Firstly, it looks dull and grey—it doesn't really stand out and grab the player's attention. Secondly, the coin cannot actually be collected yet. Certainly, the player can walk into the coin, but nothing appropriate happens in response.

Figure...

Defining game logic, rules, and behavior often requires scripting. Specifically, to transform a static and lifeless scene with objects into an environment that does something, a developer needs to code behaviors. It requires someone to define how things should act and react under specific conditions. The coin collection game is no exception to this. In particular, it requires three main features:

There's no default out-of-the-box functionality included with Unity to handle this scenario. So we must write some code to achieve it. Unity supports two languages, namely, UnityScript (sometimes called JavaScript) and C#. Both are capable and useful languages, but this book uses C# because, going forward, support for JavaScript will eventually be dropped. Let's start coding these three features in sequence. To create a new script file,...

The coin collection game wouldn't really be much of a game if there were only one coin. The central idea is that a level should feature many coins, all of which the player should collect before a timer expires. Now, to know whether all coins have been collected, we'll need to know how many coins there are in total in the scene. After all, if we don't know how many coins there are, then we can't know if we've collected them all. So, our first task in scripting is to configure the Coin class so that we can know the total number of coins in the scene at any moment easily. Consider Code Sample 2.3, which adapts the Coin class to achieve this:

//-------------------------
using UnityEngine;
using System.Collections;
//-------------------------
public class Coin : MonoBehaviour 
{
  //-------------------------
  //Keeps track of total coin count in scene
  public static int CoinCount = 0;
  //-------------------------
  // Use this for initialization
  void Start () 
{
    //Object...

Previously, we developed a coin counting variable telling us how many coins are in the scene. However, regardless of the count, the player still can't collect the coins during gameplay. Let's fix this now. To start, we need to think about collisions. Thinking carefully, we know that a coin is considered collected whenever the player walks into it, that is, a coin is collected when the player and the coin intersect or collide.

To determine when a collision happens like that, we must approximate the volume of both the player and coin in order to determine when the two volumes overlap in space. This is achieved in Unity through colliders. Colliders are special physics objects attached to meshes. They tell us when two meshes intersect. The FPSController object (First-person controller) already has a collider on it, through its Character Controller component. This approximates the physical body of a generic person. This can be confirmed by selecting FPSController in the Scene...

The basic coin functionality is now created, but the scene needs more than one coin. The problem with simply duplicating a coin and scattering the duplicates is that if we make a change later to one coin and need to propagate that change to all other coins, we'd need to delete the former duplicates and manually replace those with newer and amended duplicates. To avoid this tedious repetition, we can use prefabs. Prefabs let you convert an object in the scene to Assets in the Project panel. This can be instantiated in the scene as frequently as needed, as though it were a mesh asset. The advantage is that changes made to the asset are automatically applied to all instances automatically, even across multiple scenes.

This makes it easier to work with custom assets, so let's prefab the coin right now. To do this, select the Coin object in the scene and then drag and drop it in the Project panel. When this happens, a new prefab is created. The object in the scene is automatically...