Unity Game Development Essentials: If you have ambitions to be a game developer this guide is a must. Covering all the fundamentals of the Unity game engine, it will help you understand the different elements of 3D game creation through practical projects.

If you have worked with any 3D artworking application before, you'll likely be familiar with the concept of the Z-axis. The Z-axis, in addition to the existing X for horizontal and Y for vertical, represents depth. In 3D applications, you'll see information on objects laid out in X, Y, Z — format this is known as the Cartesian coordinate method. Dimensions, rotational values, and positions in the 3D world can all be described in this way. In this book, like in other documentation of 3D, you'll see such information written with parenthesis, shown as follows:

(10, 15, 10)

This is mostly for neatness, and also due to the fact that in programming, these values must be written in this way. Regardless of their presentation, you can assume that any sets of three values separated by commas will be in X, Y, Z order.

A crucial concept to begin looking at is the difference between Local space and World space. In any 3D package, the world you will work in is technically infinite, and it can be difficult to keep track of the location of objects within it. In every 3D world, there is a point of origin, often referred to as zero, as it is represented by the position (0,0,0).

All world positions of objects in 3D are relative to world zero. However, to make things simpler, we also use Local space (also known as Object space) to define object positions in relation to one another. Local space assumes that every object has its own zero point, which is the point from which its axis handles emerge. This is usually the center of the object, and by creating relationships between objects, we can compare their positions in relation to one another. Such relationships, known as parent-child relationships, mean that we can calculate distances from other objects using Local space, with the parent object's position becoming the new zero point for any of its child objects. For more information on parent-child relationships, see Chapter 3.

You'll also see 3D vectors described in Cartesian coordinates. Like their 2D counterparts, 3D vectors are simply lines drawn in the 3D world that have a direction and a length. Vectors can be moved in world space, but remain unchanged themselves. Vectors are useful in a game engine context, as they allow us to calculate distances, relative angles between objects, and the direction of objects.

Cameras are essential in the 3D world, as they act as the viewport for the screen. Having a pyramid-shaped field of vision, cameras can be placed at any point in the world, animated, or attached to characters or objects as part of a game scenario.

With adjustable Field of Vision (FOV), 3D cameras are your viewport on the 3D world. In game engines, you'll notice that effects such as lighting, motion blurs, and other effects are applied to the camera to help with game simulation of a person's eye view of the world — you can even add a few cinematic effects that the human eye will never experience, such as lens flares when looking at the sun!

Most modern 3D games utilize multiple cameras to show parts of the game world that the character camera is not currently looking at — like a 'cutaway' in cinematic terms. Unity does this with ease by allowing many cameras in a single scene, which can be scripted to act as the main camera at any point during runtime. Multiple cameras can also be used in a game to control the rendering of particular 2D and 3D elements separately as part of the optimization process. For example, objects may be grouped in layers, and cameras may be assigned to render objects in particular layers. This gives us more control over individual renders of certain elements in the game.

In constructing 3D shapes, all objects are ultimately made up of interconnected 2D shapes known as polygons. On importing models from a modelling application, Unity converts all polygons to polygon triangles. Polygon triangles (also referred to as faces) are in turn made up of three connected edges. The locations at which these vertices meet are known as points or vertices. By knowing these locations, game engines are able to make calculations regarding the points of impact, known as collisions, when using complex collision detection with Mesh Colliders, such as in shooting games to detect the exact location at which a bullet has hit another object. By combining many linked polygons, 3D modelling applications allow us to build complex shapes, known as meshes. In addition to building 3D shapes, the data stored in meshes can have many other uses. For example, it can be used as surface navigational data by making objects in a game, by following the vertices.

In game projects, it is crucial for the developer to understand the importance of polygon count. The polygon count is the total number of polygons, often in reference to a model, but also in reference to an entire game level. The higher the number of polygons, the more work your computer must do to render the objects onscreen. This is why, in the past decade or so, we've seen an increase in the level of detail from early 3D games to those of today — simply compare the visual detail in a game, such as Id's Quake (1996) with the details seen in a game, such as Epic's Gears Of War (2006). As a result of faster technology, game developers are now able to model 3D characters and worlds for games that contain a much higher polygon count and this trend will inevitably continue.

Materials are a common concept to all 3D applications, as they provide the means to set the visual appearance of a 3D model. From basic colors to reflective image-based surfaces, materials handle everything.

Starting with a simple color and the option of using one or more images — known as textures — in a single material, the material works with the shader, which is a script in charge of the style of rendering. For example, in a reflective shader, the material will render reflections of surrounding objects, but maintain its color or the look of the image applied as its texture.

In Unity, the use of materials is easy. Any materials created in your 3D modelling package will be imported and recreated automatically by the engine and created as assets to use later. You can also create your own materials from scratch, assigning images as texture files, and selecting a shader from a large library that comes built-in. You may also write your own shader scripts, or implement those written by members of the Unity community, giving you more freedom for expansion beyond the included set.

Crucially, when creating textures for a game in a graphics package such as Photoshop, you must be aware of the resolution. Game textures are expected to be square, and sized to a power of 2. This means that numbers should run as follows:

Creating textures of these sizes will mean that they can be tiled successfully by the game engine. You should also be aware that the larger the texture file you use, the more processing power you'll be demanding from the player's computer. Therefore, always remember to try resizing your graphics to the smallest power of 2 dimensions possible, without sacrificing too much in the way of quality.

For developers working with game engines, physics engines provide an accompanying way of simulating real-world responses for objects in games. In Unity, the game engine uses Nvidia's PhysX engine, a popular and highly accurate commercial physics engine.

In game engines, there is no assumption that an object should be affected by physics —firstly because it requires a lot of processing power, and secondly because it simply doesn't make sense. For example, in a 3D driving game, it makes sense for the cars to be under the influence of the physics engine, but not the track or surrounding objects, such as trees, walls, and so on — they simply don't need to be. For this reason, when making games, a Rigid Body component is given to any object you want under the control of the physics engine.

Physics engines for games use the Rigid Body dynamics system of creating realistic motion. This simply means that instead of objects being static in the 3D world, they can have the following properties:

As the power of hardware and software increases, rigid body physics is becoming more widely applied in games, as it offers the potential for more varied and realistic simulation. We'll be utilizing rigid body dynamics as part of our game in Chapter 6.

While more crucial in game engines than in 3D animation, collision detection is the way we analyze our 3D world for inter-object collisions. By giving an object a Collider component, we are effectively placing an invisible net around it. This net mimics its shape and is in charge of reporting any collisions with other colliders, making the game engine respond accordingly. For example, in a ten-pin bowling game, a simple spherical collider will surround the ball, while the pins themselves will have either a simple capsule collider, or for a more realistic collision, employ a Mesh collider. On impact, the colliders of any affected objects will report to the physics engine, which will dictate their reaction, based on the direction of impact, speed, and other factors.

In this example, employing a mesh collider to fit exactly to the shape of the pin model would be more accurate but is more expensive in processing terms. This simply means that it demands more processing power from the computer, the cost of which is reflected in slower performance — hence the term expensive.

If I wished to have a bouncing ball as part of a game, then I'd begin with a sphere. This can quickly be created from the Unity menus, and will give you a new Game Object with a sphere mesh (a net of a 3D shape), and a Renderer component to make it visible. Having created this, I can then add a Rigid body. A Rigidbody (Unity refers to most two-word phrases as a single word term) is a component which tells Unity to apply its physics engine to an object. With this comes mass, gravity, and the ability to apply forces to the object, either when the player commands it or simply when it collides with another object. Our sphere will now fall to the ground when the game runs, but how do we make it bounce? This is simple! The collider component has a variable called Physic Material — this is a setting for the Rigidbody, defining how it will react to other objects' surfaces. Here we can select Bouncy, an available preset, and voila! Our bouncing ball is complete, in only a few clicks.

This streamlined approach for the most basic of tasks, such as the previous example, seems pedestrian at first. However, you'll soon find that by applying this approach to more complex tasks, they become very simple to achieve. Here is an overview of those key Unity concepts plus a few more.

The Scene window is where you will build the entirety of your game project in Unity. This window offers a perspective (full 3D) view, which is switchable to orthographic (top down, side on, and front on) views. This acts as a fully rendered 'Editor' view of the game world you build. Dragging an asset to this window will make it an active game object. The Scene view is tied to the Hierarchy, which lists all active objects in the currently open scene in ascending alphabetical order.

The Scene window is also accompanied by four useful control buttons, as shown in the previous image. Accessible from the keyboard using keys Q, W, E, and R, these keys perform the following operations:

Having selected objects in either the Scene or Hierarchy, they immediately get selected in both. Selection of objects in this way will also show the properties of the object in the Inspector. Given that you may not be able to see an object you've selected in the Hierarchy in the Scene window, Unity also provides the use of the F key, to focus your Scene view on that object. Simply select an object from the Hierarchy, hover your mouse cursor over the Scene window, and press F.

Think of the Inspector as your personal toolkit to adjust every element of any game object or asset in your project. Much like the Property Inspector concept utilized by Adobe in Flash and Dreamweaver, this is a context-sensitive window. All this means is that whatever you select, the Inspector will change to show its relevant properties — it is sensitive to the context in which you are working.

The Inspector will show every component part of anything you select, and allow you to adjust the variables of these components, using simple form elements such as text input boxes, slider scales, buttons, and drop-down menus. Many of these variables are tied into Unity's drag-and-drop system, which means that rather than selecting from a drop-down menu, if it is more convenient, you can drag-and-drop to choose settings.

This window is not only for inspecting objects. It will also change to show the various options for your project when choosing them from the Edit menu, as it acts as an ideal space to show you preferences — changing back to showing component properties as soon as you reselect an object or asset.

In this screenshot, the Inspector is showing properties for a target object in the game. The object itself features two components — Transform and Animation. The Inspector will allow you to make changes to settings in either of them. Also notice that to temporarily disable any component at any time which — will become very useful for testing and experimentation — you can simply deselect the box to the left of the component's name. Likewise, if you wish to switch off an entire object at a time, then you may deselect the box next to its name at the top of the Inspector window.

The Project window is a direct view of the Assets folder of your project. Every Unity project is made up of a parent folder, containing three subfolders — Assets, Library, and while the Unity Editor is running, a Temp folder. Placing assets into the Assets folder means you'll immediately be able to see them in the Project window, and they'll also be automatically imported into your Unity project. Likewise, changing any asset located in the Assets folder, and resaving it from a third-party application, such as Photoshop, will cause Unity to reimport the asset, reflecting your changes immediately in your project and any active scenes that use that particular asset.

The Project window is accompanied by a Create button. This allows the creation of any assets that can be made within Unity, for example, scripts, prefabs, and materials.

The Game window is invoked by pressing the Play button and acts as a realistic test of your game. It also has settings for screen ratio, which will come in handy when testing how much of the player's view will be restricted in certain ratios, such as 4:3 (as opposed to wide) screen resolutions. Having pressed Play, it is crucial that you bear in mind the following advice:

The Game window can also be set to Maximize when you invoke play mode, giving you a better view of the game at nearly fullscreen — the window expands to fill the interface. It is worth noting that you can expand any part of the interface in this way, simply by hovering over the part you wish to expand and pressing the Space bar.