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Before getting started with any 3D package, it is crucial to understand the environment you'll be working in. This article by Will Goldstone covers the key 3D concepts and processes we'll need to understand to create games in Unity.
Getting to grips with 3D
Let's take a look at the crucial elements of 3D worlds, and how Unity lets you develop games in the third dimension.
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 any 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.
Local space versus World space
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.
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.
Polygons, edges, vertices, and meshes
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, textures, and shaders
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:
- 128 x 128
- 256 x 256
- 512 x 512
- 1024 x 1024
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.
Rigid Body physics
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.
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.
Essential Unity concepts
Unity makes the game production process simple by giving you a set of logical steps to build any conceivable game scenario. Renowned for being non-game-type specific, Unity offers you a blank canvas and a set of consistent procedures to let your imagination be the limit of your creativity. By establishing its use of the Game Object (GO) concept, you are able to break down parts of your game into easily manageable objects, which are made of many individual Component parts. By making individual objects within the game and introducing functionality to them with each component you add, you are able to infinitely expand your game in a logical progressive manner. Component parts in turn have variables—essentially settings to control them with. By adjusting these variables, you'll have complete control over the effect that Component has on your object. Let's take a look at a simple example.
The Unity way
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.
These are the building blocks of all Unity projects. From graphics in the form of image files, through 3D models and sound files, Unity refers to the files you'll use to create your game as assets. This is why in any Unity project folder all files used are stored in a child folder named Assets.
In Unity, you should think of scenes as individual levels, or areas of game content (such as menus). By constructing your game with many scenes, you'll be able to distribute loading times and test different parts of your game individually.
When an asset is used in a game scene, it becomes a new Game Object—referred to in Unity terms—especially in scripting—using the contracted term "GameObject". All GameObjects contain at least one component to begin with, that is, the Transform component. Transform simply tells the Unity engine the position, rotation, and scale of an object—all described in X, Y, Z coordinate (or in the case of scale, dimensional) order. In turn, the component can then be addressed in scripting in order to set an object's position, rotation, or scale. From this initial component, you will build upon game objects with further components adding required functionality to build every part of any game scenario you can imagine.
Components come in various forms. They can be for creating behavior, defining appearance, and influencing other aspects of an object's function in the game. By 'attaching' components to an object, you can immediately apply new parts of the game engine to your object. Common components of game production come built-in with Unity, such as the Rigidbody component mentioned earlier, down to simpler elements such as lights, cameras, particle emitters, and more. To build further interactive elements of the game, you'll write scripts, which are treated as components in Unity.
Unity does not require you to learn how the coding of its own engine works or how to modify it, but you will be utilizing scripting in almost every game scenario you develop. The beauty of using Unity scripting is that any script you write for your game will be straightforward enough after a few examples, as Unity has its own built-in Behavior class—a set of scripting instructions for you to call upon. For many new developers, getting to grips with scripting can be a daunting prospect, and one that threatens to put off new Unity users who are simply accustomed to design only. I will introduce scripting one step at a time, with a mind to showing you not only the importance, but also the power of effective scripting for your Unity games.
To write scripts, you'll use Unity's standalone script editor. On Mac, this is an application called Unitron, and on PC, Uniscite. These separate applications can be found in the Unity application folder on your PC or Mac and will be launched any time you edit a new script or an existing one. Amending and saving scripts in the script editor will immediately update the script in Unity. You may also designate your own script editor in the Unity preferences if you wish.
Unity's development approach hinges around the GameObject concept, but it also has a clever way to store objects as assets to be reused in different parts of your game, and then 'spawned' or 'cloned' at any time. By creating complex objects with various components and settings, you'll be effectively building a template for something you may want to spawn multiple instances of, with each instance then being individually modifiable. Consider a crate as an example—you may have given the object in the game a mass, and written scripted behaviors for its destruction; chances are you'll want to use this object more than once in a game, and perhaps even in games other than the one it was designed for.
Prefabs allow you to store the object, complete with components and current configuration. Comparable to the MovieClip concept in Adobe Flash, think of prefabs simply as empty containers that you can fill with objects to form a data template you'll likely recycle.
The Unity interface, like many other working environments, has a customizable layout. Consisting of several dockable spaces, you can pick which parts of the interface appear where. Let's take a look at a typical Unity layout:
As the previous image demonstrates (PC version shown), there are five different elements you'll be dealing with:
- Scene —where the game is constructed
- Hierarchy —a list of GameObjects in the scene
- Inspector —settings for currently selected asset/object
- Game —the preview window, active only in play mode
- Project —a list of your project's assets, acts as a library
The Scene window and Hierarchy
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:
- The Hand tool [Q]: This tools allows navigation of the Scene window. By itself, it allows you to drag around in the Scene window to pan your view. Holding down Alt with this tool selected will allow you to rotate your view, and holding the Command key (Apple) or Ctrl key (PC) will allow you to zoom. Holding the Shift key down also will speed up both of these functions.
- The Translate tool [W]: This is your active selection tool. As you can completely interact with the Scene window, selecting objects either in the Hierarchy or Scene means you'll be able to drag the object's axis handles in order to reposition them.
- The Rotate tool [E]: This works in the same way as Translate, using visual 'handles' to allow you to rotate your object around each axis.
- The Scale tool [R]: Again, this tool works as the Translate and Rotate tools do. It adjusts the size or scale of an object using visual handles.
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
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.
It is important to remember that you should only alter asset locations and names using the Project window—using Finder (Mac) or Windows Explorer (PC) to do so may break connections in your Unity project. Therefore, to relocate or rename objects in your Assets folder, use Unity's Project window instead.
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
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:
In play mode, the adjustments you make to any parts of your game scene are merely temporary—it is meant as a testing mode only, and when you press Play again to stop the game, all changes made during play mode will be undone. This can often trip up new users, so don't forget about it!
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.
Here we have looked at the key concepts, you'll need to understand for developing games with Unity. Due to space constraints, I cannot cover everything in depth, as 3D development is a vast area of study. With this in mind, I strongly recommend you to continue to read more on the topics discussed in this article, in order to supplement your study of 3D development. Each individual piece of software you encounter will have its own dedicated tutorials and resources dedicated to learning it. If you wish to learn 3D artwork to complement your work in Unity, I recommend that you familiarize yourself with your chosen package, after researching the list of tools that work with the Unity pipeline and choosing which one suits you best.
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About the Author :
Will Goldstone is a longstanding member of the Unity community and works for Unity Technologies as a Technical Support Associate, handling educational content and developer support. With an MA in Creative Education, and many years experience as a lecturer in higher education, Will wrote the first ever Unity book, the original Unity Game Development Essentials, and also created the first ever video tutorials for the package. Through his sites http://www.unity3dstudent.com and http://learnunity3d.com Will helps to introduce new users to the growing community of developers discovering Unity every day.