Tower defense games come in many different styles. For example, in the following screenshot of Defense Grid: The Awakening and Unstoppable Gorg, both are top-down isometric style games. However, they are set in different worlds, with different objectives. So, given this, what makes a tower defense game? For one, they are centered on the idea of defending something, whether it is buildings, resources, weapons, and so forth. This is the main mechanism that defines the genre and drives the gameplay. Secondly, most tower defense games require economic and resource management. For example, after each wave of enemies, you may obtain a certain amount of virtual currency that you must then allocate to either the purchase of new defenses (weapons, towers, and so on) or upgrades. Each has their benefits depending on a range of factors such as weak points in your defense as well as the anticipated amount and strength of enemies that will be in the next wave. The number and difficulty of enemies increases after each wave, therefore challenging the player to manage resources and build defenses strategically. The idea is to build up enough resources to upgrade your defenses and to outlast the incoming wave. Sometimes, the player must stop the enemies (or an opponent) from destroying their own base.

In other cases, the player must prevent the enemies from reaching the end, as each enemy that manages to get through cause damage to the player's health bar.

(Top) Defense Grid: The Awakening and (bottom) Unstoppable Gorg

There are many places on the Internet where you can find tower defense games. For example, Kongregate (http://www.kongregate.com/) and Newgrounds (http://www.newgrounds.com/) are examples of sites where a varied array of free tower defense games exist (such as Kingdom Rush or Bloons Tower Defense 5). However, many exist for iOS (App Store) and Android (Play Store), operating systems such as Linux, OSX, and PC (for example, Steam), and consoles (Playstation, Xbox), and so on.

Before you even think about turning your computer on, you need to design your game. It's not enough to have a rough idea in mind. You need to write down all your ideas before hand to start working. The first phase of game design is brainstorming. There are different techniques and methodologies of brainstorming that, unfortunately, we don't have the time, in this small section, to describe. However, the final outcome should be tons of paper with thousands of ideas written down. It's not meant to be a work of art, but the foundations upon which your game will be built.

The next step is to refine your ideas, discard (or keep for other projects) the ones that you don't need, and organize them in a coherent form.

The final result should be something like the following.

From this excerpt, you are now able to understand what we are going to do in this book. You also have a basic idea of how to write down your ideas. I strongly suggest that you always do this step, even when you are the only developer, and especially when you have a team.

Now that we have our idea, the next thing to do is to get Unity. It comes in different versions: Personal (which is free), Plus, Professional, and Enterprise. The last three contain more features than the Personal one. However, all the topics covered in this book can be done with the free version. In any case, you can get or buy Unity on the official website: www.unity3d.com.

This is the comparison screen between the different versions of Unity on the Unity Technologies website (if you scroll down, you will find which feature is included in which version):

Note

This is a very short summary of how model pricing for Unity has varied in recent years. In fact, to become a developer also means to be aware of the world around you, and having basic marketing knowledge could also help. At the beginning, the model price of Unity didn't allow developers to publish commercial games with the free version. In addition, the game engine didn't have all the features, such as the Profiler or the Movie Textures. Epic Games, the company that owns Unreal Engine, changed its model prices by making its game engine free in March 2015, also for commercial use (although it will take in return the 5% of the game's gross revenue). After a period of time, Unity Technologies also allowed developers to publish commercial games even with the free version, but it was still watermarked. From Unity 5.x, features that were only in the Pro version became available in the free version as well. During the beginning of 2016, Unity used to come in two different versions: Free (or Personal) and Professional. The latter contains more features than the Personal one, and here is the comparison screen of the two:

In June 2016, Unity changed its price model in the one described earlier.

Once we have installed Unity, we can begin creating new projects. If we click on the New project button in the top-right corner of the window, Unity will ask us to insert the details for our project. We can name it Panda Invasion and choose the destination path, which is where the files of the project will be stored. There is another an important thing to note. Unity gives us the possibility to choose between a 3D and a 2D project. This is not important decision, since it can be changed at any time. However, it is useful to already have in mind whether or not the game will be 2D or 3D. By selecting the 2D mode, Unity adapts the default settings to the game that we have in mind. We will see these settings in the following sections. For now, you should have a screen that looks like the following:

Now, we can press the Create project button, and we have successfully created our project and are ready to build it.

This book assumes that you are fairly familiar with the Unity interface and with C# code. If you are not, don't worry. There are different ways that you can learn before continuing on with this book. For example, I wrote a small free e-guide that briefly goes through the main interfaces and concepts of Unity. Don't expect to learn all you need from there, but it is a good start. You can find it at https://www.packtpub.com/packt/free-ebook/what-you-need-know-about-unity-5. If you are a complete newcomer to Unity, please read that small e-guide. I'll still be here once you have finished and we can resume our awesome journey. Furthermore, the official manual of Unity and its documentation are great companions in the Unity game development world. You can find them both on the official website, at https://docs.unity3d.com/Manual/index.html.

Since we don't have the time to create our own graphics for the game that we are going to develop, we need to download a custom package. Of course, you are free to choose the one you like most. For this book, we are going to use the Tower Defence Pack 2 package, which can be downloaded from http://player26.com/.

The package includes all the basic assets that we need to create our tower defense game. It is free, even for commercial use, and even if credits are required. There is also a premium version that contains more assets and some of the decorations in different Sprites to increase customizability. In particular, in the free version we can find:

The following image can give you an idea of the kind of graphics this package contains:

So, download this package before moving on to the next section.

If you are new to Unity, or you have only used Unity 5.x, you can skip this section or read it just for curiosity.

In Unity 4.x (before version 4.6) and other previous versions, building 2D games was a bit harder. In fact, you needed to use a range of different methods and tricks to achieve the illusion on 2D. All the 2D objects were actually 3D objects viewed in a particular perspective or with a particular camera, which gave the illusion of a 2D object.

From Unity 4.6 on, and especially since Unity 5.x, this is not needed any more. There is built-in support for 2D games. So now, there are special components to deal with 2D objects, and the following sections will explore some of them.

There are different ways to organize a project within Unity, therefore giving a bit more freedom. In this section, we propose one method, which we will use during the development of the project in this book.

The key idea is to organize the different assets by type (and not, as in other methods, by their position within the level).

First of all, let's understand how Unity organizes assets. All of them are placed inside a folder named Assets, which can be found also inside the Project folder. Therefore, all our assets should be contained in this folder or subfolder. In order to create a new folder, right-click on the Project panel and then Create | Folder. As a result, a new folder is created within the folder you clicked. Since we don't have any folders, it will be a subfolder of the Assets one. We have the option to rename it as we want. If you miss this, you can just select it and then click on it again (but not too fast, otherwise Unity will consider this as a double-click and it will open the folder), as shown in the following screenshot:

We need to create the following folders (you should only create the ones in bold, since we will not use the other ones):

At the end, we should see the following in our Project panel (I'll add the Animation folder in Chapter 4, No Longer Alone - Sweet-Toothed Pandas Strike, when we will see animations, but feel free to add it immediately if you like):

There is something else to know about the folders in your projects. If you create folders with some specific names, Unity will treat them in a special way. We are not going to use them; however, it's worth giving them a quick look:

Coming back to our folder, we need to import the package that we have downloaded. This can be done in a number of different ways, but the easiest way is to drag and drop the folder of the package within our Graphics folder.

If you need to select an asset to use, in the bottom-left corner of the Project panel, there is a slider that allows you to increase the size of the icons in the Project panel. This function is useful when there are a lot of assets and we need to find the right one without knowing the name, or when exploring new packages we don't know yet. The slider is highlighted in the following screenshot for your convenience:

There are few things to notice in our project when it is set to 2D mode, which we are going to explore in this section.

First of all, if you ever need to switch between 2D and 3D mode, you can do so by navigating to Edit | Project Settings | Editor. If you go in to the Default Behavior Mode settings, you can change the Mode, as shown in the following screenshot:

Coming back to our main interface, let's see the main differences between 2D and 3D mode. The Scene view is set by default to 2D, as you can see in the following screenshot:

This allows us to have the Scene view locked on to the xy plane.

Then, every time we create a new scene, the default camera that comes with it is always set in Orthographic mode. Furthermore, its position is set to (0, 0, -10), whereas in 3D mode, it is set to (0, 1, -10). You can also check this by selecting the Main Camera in the Hierarchy panel and seeing its properties in the Inspector, as shown in the following screenshot:

Other differences are the options to use the Sprite Packer or the default objects that don't have real-time directional lights. There are also changes in the Lighting settings (you can access them from Window/Lighting). In particular, the Skybox is disabled for new scenes and Precomputed Realtime GI, Baked GI, and Auto-Building are set to off. In addition, the Ambient Source comes with a dark grey color.

In the following screenshot, you can see the default Lighting settings:

However, the most important difference is how Unity imports new 2D assets, but we are going to see this in detail in the following sections.