Before we do anything, we need a player Sprite or image. For our Perky Penguin game, we have designed a penguin sprite. The following figure shows the penguin that is included as the player sprite of the game:

Figure 1.35 Penguin Sprite

To import an image in to Unity, right-click on the Graphics folder in the Project Browser panel and click on Import New Asset..., as shown in the following screenshot:

Figure 1.36 Import New Asset in Unity

These assets can be anything that is supported by Unity, such as images, audio files, 3D models, textures, materials, and scripts.

Unity shows all the images with nice previews. It must be noted here that if Unity is in 2D mode, then unity will show images as sprites and if mode is set to 3D mode it shows the images as textures. Figure 1.36 shows both scenarios. The following screenshot shows the image imported as sprite and the screenshot besides it shows image imported as texture:

Figure 1.37 Images as Sprites (left) and Images as Textures (right)

If the penguin image is imported as texture, then there is nothing to worry about. Select the image from Project Browser panel, and in the inspector change the Texture Type to Sprite and click Apply. It is shown in the following figure:

Figure 1.38 Change Texture Type of Image in Inspector Panel

After the assets are imported, which in our case is a single penguin image, we have to create a game object of player. Usually game objects are created by right-clicking in Hierarchy and selecting Create Empty as shows in the following figure:

Figure 1.39 Creating Empty Game Object

But, in order to create sprites as game objects, simply drag sprites from the Project Browser panel to Hierarchy or Scene View panels and a game object will be created with the name of image file which is penguin_fly.png here. This is shown in the following figure:

Figure 1.40 Creating Sprite Game Object

Now it's time to configure the penguin_fly game object of Hierarchy to get used in the game. Now select the penguin_fly object and make following changes in the Inspector panel.

Figure 1.41 Adding Circle Collider 2D

Figure 1.42 Adding Rigid Body 2D

The following figure below shows all the steps performed on the penguin game object:

Figure 1.43 Penguin Inspector Settings

Starting from position, we have set the position to zero just for testing purposes. We will change it later when we put penguin at its initial position. The Sprite Renderer component is already added in the penguin game object because penguin game object was created from sprite by dragging it from Project Browser panel. The Sprite Renderer allows any game object to show an image on the screen from any sprite. In order to make any game object to react to physics collisions and get collided with each other, game object requires collider component in it. We have added Circle Collider 2D on the penguin object. You can choose any type of collider from the list. But it is recommended to choose the collider which is very light and fills the whole colliding area. The following figure shows the penguin with different colliders applied to it:

Figure 1.44 Penguins with Different Colliders

Using complex colliders like Polygon Collider 2D makes it harder to detect collision for the physics engine to detect collision, which in turn, creates a performance penalty. Finally, in order to apply gravity on the penguin, we have added Rigid Body 2D component. Rigid Body 2D allows any game objects to behave to the gravity, friction, physics kinematics and so on. We have check Fixed Angle to on state of the Rigid Body 2D. If this is set to off, then penguin will also rotate due to wind, friction, gravity, or any other force applied on it. So in order to avoid her to rotate while jumping, we have set Fixed Angle as checked.

When you run the project, you will notice that penguin will fall down on the screen. It is because of the gravity is pulling penguin downwards and it goes off the screen. The Gravity Scale value, which is 1 by default, decides the gravity of the penguin. If we remove or disable Rigid Body 2D component, then penguin will never move. So, it must be noted that without rigid body no force and collision will be applied on the game object.

After setting physics components and position on penguin object, it's time to define some logic behavior of the penguin. The game's requirements are to let penguin fly through its jetpack when screen is touched by player and penguin will fall when touch is stopped. These kinds of logic are defined in Unity through scripts. Unity supports 2 kinds of scripts; C# and JavaScript. You can use any of these scripts. Even you can also use few files in C# and few other files in JavaScript in the same project. Throughout this book, we will do all the scripting through C#.

Figure 1.45 Adding a C# Script

Figure 1.46 A C# Script File in MonoDevelop

Figure 1.47 Adding C# Script on Penguin GameObject

Now, as the script is applied on the penguin game object, let's write some logic and code to make the penguin fly. Open PenguinController.cs file from project browser panel by double-clicking it in MonoDevelop. The code which is already written looks like the following screenshot:

        public float jetpackForce = 75.0f;

Figure 1.48 The jetpackForce Field in the Inspector Panel

        void FixedUpdate()
        {
            bool jetpackkActive = Input.GetButton ("Fire1);
            if (jetpackActive = true) {
                this.GetComponent<Rigidbody>().AddForce(new Vector2(0, 
                jetpackForce));
            }
        }

Following is the whole PenguinController.cs file's code: 

Figure 1.49 Gravity Scale of Penguin (left) and Gravity of Physics2D (right)

We will change the Gravity value of Physics2D settings to -15. You can open Physics2D settings from Edit - Project Settings - Physics2D menu.

Now run the game, and you will notice the penguin will fall slower than before. On clicking many times, you might notice that penguin gets out of the screen. This kind of behavior in the games should be avoided. So, in order to limit the penguin within the screen bounds, we will add floor and ceiling in the game. Let's see how it's done in the next section.

Adding floor and ceiling is quite simpler job. We will create an empty object first. It should be noted that we are not importing any images or sprite assets in the scene, because we only need boundaries not the visuals of those about how these will look. Here is how we create our floor object.

Now you should be seeing a green rectangle on bottom of screen. This is the box collider of the floor and when you run the game, the penguin will never fall off the screen and it will stop when collided with the floor.

Similarly, now add ceiling game object with the name ceiling and its position of (0, 3.25, 0) and its scale of (14.4, 1, 1). Apply Rigid Body 2D component on the ceiling object, and now run the project. You will observe that penguin now never leaves the screen and it is limited between the upper and lower parts of the screen.