Rock Entity

Introduction

This tutorial will define the Rock entity and add it to our GameScreen so that we can shoot it. This tutorial will focus specifically on the creation of the Rock entity (adding a Sprite) as well as collision. We will revisit the creation of Rock entities in the next tutorial as well when we handle the creation of Rocks over time.

Adding a PNG and Sprite

As you might have guessed, the first step is to add PNGs and a Sprite to the Rock entity. To add the PNGs:

1. Download the following four images:

2. Expand the Rock Entity in Glue

3. Drag+drop the four files into the Files folder

Now you should have four files in the Rock entity. Like before, the PNG files will be copied into the game project. To add the Sprite to the Rock entity:

1. Select the Rock entity

2. Click the Add Object to Rock button in the Quick Actions tab
3. Select the Sprite type

4. Click OK

To set the Sprite's Texture:

1. Select the newly-added SpriteInstance

2. Select the Variables tab

3. Use the Texture drop-down to select Rock1

Considering Rock spawning

The next question we are faced with is how to handle spawning of the rocks (spawning also means to create an Entity at runtime on a time interval). Our spawn code should have the following criteria:

1. We should be able to control the difficulty of the game by increasing or reducing the rate at which Rocks spawn

2. Rocks need to appear at random locations so the player cannot predict their movement

3. Rocks should not spawn on-screen. This both looks unrealistic, and it can also be frustrating to the player if a Rock suddenly appears on top of the player

4. Rocks should move in all directions. Our game will require the player to rotate the ship to navigate in every direction, so rocks shouldn't just appear on the top of the screen.

Furthermore, we must also consider where we should put the code for Rock spawning. One option is to put the code in the GameScreen. However, we can keep our code easier to maintain if we separate this logic into its own class. Also, since we will want to have variables to control the initial spawn rate as well as how fast the spawn rate grows, we will create a new Entity to store these variables.

Creating RockSpawner

To create the RockSpawner Entity:

1. Select the Quick Actions tab

2. Click the Add Entity button
3. Enter the name RockSpawner

4. Click OK - we won't need any collision or visuals in this entity

The RockSpawner is different from our other entities - we only need a single RockSpawner instance. To add an instance to the GameScreen:

1. Select the RockSpawner

2. Click the Quick Actions tab

3. Click the Add RockSpawner Instance to GameScreen button

Next we'll add four variables to the RockSpawner. These are:

• RocksPerSecond

• SpawnRateIncrease

• MinVelocity

• MaxVelocity

To add RocksPerSecond:

1. Select the RockSpawner

2. Click the Variables tab

3. Click the Add New Variable button
4. Enter the name RocksPerSecond

5. Click OK

Repeat the steps above for the other three variables. We'll set some defaults for our variables as well:

• RocksPerSecond = 0.2

• SpawnRateIncrease = 0.015

• MinVelocity = 50

• MaxVelocity = 100

RockSpawner logic

Now that we have variables to use for spawning, we can create our spawning logic. The logic will be broken up into two parts:

1. Deciding if it's time to spawn a rock

2. Spawning a rock and giving it its initial velocity

First, we'll add the top-level logic to CustomActivity. To do this:

1. Go to Visual Studio

2. Open RockSpawner.cs

3. Modify this file so that it contains the following code