So instead we break up our game into smaller chunks and these load into memory when they are needed, hence the \u201cloading\u201d screen that so many games have. (You may be thinking \u201cbut what about sandbox games?\u201d Well, those are divided into smaller areas as well \u2013 and not just areas, even objects inside those areas have various levels of detail that can be called up. The loading of that content happens in the background, and will swap places with a lower quality model when ready, usually fading between the two so as to disguise the effect and not distract the eye. Most often this happens in the distance, and the game is using predictive algorithms to determine which content you are most likely to need yet and start to load it.)<\/p>\n\n\n\n
When Unity was first created, they also included a level system, which became known as Scenes. <\/strong>You will recognize this today as the format that we save our files in. Scenes have evolved to be much much more than just game levels, and are frequently seen used for other cases such as UI screens\/menus, code and asset loading, and animated cutscenes. Sometimes entire games will be saved as scenes. Projects (the things we open when we launch Unity, and where our Assets and such are stored) can contain multiple scenes, and when we build our game we will designate which of the scenes we create will be included in the build. (This is particularly useful when you\u2019re working on branches or variations of your game \u2013 you can simply swap one out for another if you need to!)<\/p>\n\n\n\n For our in-class demo, we changed the name of our main game scene from the Unity default \u201cSampleScene\u201d to “Level01”. We also created a new scene (“StartMenu”) to house our UI, and a quick small game scene we named “Tutorial”. <\/p>\n\n\n\n NOTE <\/strong>\u2013 Don\u2019t worry too much today about the buttons, we will take a deeper dive into the UI system in the next class.<\/p>\n\n\n\n Unity\u2019s UI buttons are easy to generate by going to Create > UI > Button<\/strong> or in the top menu GameObject > UI > Button<\/strong>. This will create a new button object as a child of the Canvas object (which will also be created if you don\u2019t already have one). Buttons consist of two parts, the Button<\/strong> object, and a child Text<\/strong> object. The Button object has two Components to note \u2013 the \u201cImage (Script)\u201d component where you define the look of your button, and the \u201cButton (Script)\u201d component where you can define the behaviors and transitions of the buttons. The default button transition is a color tint, but If you have pre-made images for your button states, you can use the \u201cSprite Swap\u201d transition to show them. The child text object is optional.<\/p>\n\n\n\n Now for the complicated part \u2013 adding an action to your button. Buttons have an \u201cOnClick()\u201d message that they send when a user clicks them but accessing them is not as simple as accessing collider messages. At the bottom of the \u201cButton (Script)\u201d component you will see an \u201cOnClick()\u201d panel that is empty. If you click the \u201c+\u201d button it will create a new action. This action requires an object to be associated with it in order to access its scripted functions. You can add a script to the Button object, but then you will have to self-associate the button with itself. NOTE: The object HAS to be an object currently in the hierarchy. Linking to a prefab does not work.<\/strong><\/p>\n\n\n\n In class, I created an empty game object (“LevelManager”) and added a script (also called “LevelManager\u201d) which contained a single function that we would use to move to the next scene (“btn_StarTheGame”). In the OnClick( ) <\/strong>menu I associate the script object and select a function from the dropdown on the right by going to the specific component \u201cLevelManager\u201d and selecting the function I want to use.<\/p>\n\n\n NOTE:<\/strong> Any function that will be accessed by a Button must be PUBLIC, and VOID. It can only take up to one (1) parameter, that parameter can only be a Float, Int, String, or Object.<\/p>\n\n\n\n Now that we have a button in place, let\u2019s connect some scenes.\u00a0 I\u2019m going to make a “LevelManager” script handle our first scene jump.<\/p>\n\n\n\n First, I have to add a new library to the code, so I start the file by adding this line:<\/p>\n\n\n\n Now we can access the scene management commands. I can create a button command, so looking at our button example above to make us jump to the Level01 scene, I create the following in button script.<\/p>\n\n\n\n Again, please note that this must public and void for the editor to see it. Here, ours takes no arguments. And the command itself is rather simple \u2013 we run the LoadScene( )<\/strong> function and pass in the string name of our level. We can also pass in an integer that corresponds with the scene index. Speaking of\u2026<\/p>\n\n\n\n In order to load scenes, Unity has to have those scenes associated with the build. You can do this by going to File > Build Settings<\/strong>, and dragging the scenes you will be using from the Asset panel into the scene list in Build Settings. Notice that when you add a scene, it also assigns it an indexed location.<\/p>\n\n\n Once you have associated the scenes, you can close the window. (There is no save button to worry about, your changes are automatically registered.)<\/p>\n\n\n\n If we are making a game, chances are we want to do things like keep track of the score, or the number of lives remaining. A GameManager script seems like the best candidate for this. We created an empty object, assigned it a GameManager script which sets up a singleton, and converted it into a prefab. We made sure to include this prefab in both of our platform game scenes, as we will need it to handle our logic for events like player deaths, inventory, and of course, the score.<\/p>\n\n\n\n We edited our Level Manager to also be a singleton (so that we can automatically access it within a scene) and added a public string to hold the name of the next scene we should visit upon successful completion of the level.<\/p>\n\n\n\n If our player successfully reaches the end of a level, we reward them by sending them to the next one. To support this, we set a trigger at the end of the level, and tagged it with a “EndOfLevel” tag. If the Player object enters the trigger with that tag, it calls the NextLevel( )<\/strong> command from the LevelManager <\/strong>and that sends the player to the appropriate scene. <\/p>\n\n\n\n In our GameManager script, we define our scene jump like so:<\/p>\n\n\n\n But now we have a problem. GameManager only exists in the scene that I created it in. As soon as I jump to a new scene, it gets destroyed just like everything else in its host scene and THAT scene\u2019s GameManager instance appears. I spent all that time collecting those coins, and now they’re gone!<\/p>\n\n\n If I want to hold onto things like my score, remaining lives, and inventory, I need to make GameManager persist across the transition from one scene to the next.<\/p>\n\n\n\n To accomplish this, we spare GameManager from an untimely deletion by adding the following line to the Start ( )<\/strong> function in the GameManager script.<\/p>\n\n\n\n DontDestroyOnLoad ( )<\/strong> preserves a game object across transitions. It actually creates a little side scene in the Hierarchy and moves the object into it during runtime, as seen below:<\/p>\n\n\n Now when we jump scenes, this object remains, and our score persists as we play through.<\/p>\n\n\n\n But\u2026 (you knew there would be one, didn\u2019t you?)<\/p>\n\n\n\n For our game to run correctly, we need to have GameManager running in every scene. This means that either we would ALWAYS have to start our game from the very beginning in the scene where we first instantiate it and play all the way through \u2013 not fun, especially when we just want to test one tiny thing in level 5 \u2013 OR we have to find a way to include it in EVERY scene. This is why we chose to make our Game Manager a prefab, and drop an instance of it into every level.<\/p>\n\n\n\n But\u2026 if we are not destroying our Game Manager and we load a scene with another instance of Game Manager, won\u2019t there be two Game Managers?<\/p>\n\n\n\n Yes there will, and that is a problem. Because now not only do we have two game managers, the new one has just declared itself the singleton (S = this) and overwritten the old one, meaning the new object\u2019s score is the one we display and that\u2019s not what we want at all, is it? And if we move scenes again, since both of these now live within the DontDestroyOnLoad section, we will be adding a third Game Manager and overwritting our Singleton yet again and this seems bad.<\/p>\n\n\n\n So to avoid this situation, we create a small workaround. We build in a check in our Game Manager start script that checks to see if any instance of the singleton exists. If none exists, great \u2013 we\u2019re first to the party and we set up shop. But if there is already a singleton defined, we kill this instance of the manager as it is not needed. The script for that looks like this:<\/p>\n\n\n\n Here we check for the existence of another version of GameManager. If none exists, GameManager.S will return \u201cnull\u201d. If not null, someone is already here. We destroy this new version, and we submit a \u201creturn\u201d command, which exits our script rather than continuing on.<\/p>\n\n\n Once we\u2019ve passed our null-check, the script is still executing so we know we must be the one true game manager. We assign Singleton status and then in the Start( ) <\/strong>method we declare our intention to live forever.<\/p>\n\n\n\n What about when we DO want something to disappear? In the case of our game flow, how do we reset a game if we reach a win or lose state? How to do we go from zero lives remaining back to three, to full health, to an empty inventory? We could write an elaborate script to reset our conditions internally, but the easier method would be to simply let the GameManager die, return to the Title Screen, and let the next GameManager that comes along start the process all over again.<\/p>\n\n\n\n It turns out that the answer to this is quite simple – we Destroy( )<\/strong> the Game Manager from within itself. DontDestroyOnLoad <\/strong>only preserves objects across transitions – it does not make them immortal.<\/p>\n\n\n\n In this example, we are returning to the title screen (for whatever reason) and we remove the GameManager object.<\/p>\n\n\n\n My favorite method for managing death and respawning in a platform game is to simply restart the level by reloading it. This means that all objects in the scene will be destroyed and re-instantiated. <\/p>\n\n\n\n Here is a sample script of how you could handle this, by checking for lives remaining. (NOTE: this is not what we implemented in class today)<\/p>\n\n\n\n Here, if my Player dies but I still have lives left, my GameManager script calls RestartLevel( )<\/strong> which simply loads the same scene by passing it the name of the current active scene. It is a simple and clean solution, if you don’t need to preserve the state of objects or items within the level.<\/p>\n\n\n\n If you DO need to preserve states or items , you can store this information in your undestroyed game manager and when the level restarts, have the objects check for relevant data. For instance, if you were building checkpoints into your game you could store a “checkpoint” value with a unique ID for where to place the player. <\/p>\n\n\n\n Better yet, you could make a Level Manager which would store the states of the objects in the level itself, but which would destroy itself when your script moved on to the next level. Then you have a GameManager that lives across the game, and a LevelManager that lives across attempts at a level.<\/p>\n\n\n\n In class, the GameManager was not properly destroying itself. This is due to a missing “else” statement on line 22. This has been corrected for the code below.<\/p>\n\n\n\nPart 2 – Setting up Buttons<\/h3>\n\n\n\n
![\"\"](\"https:\/\/courses.ideate.cmu.edu\/53-353\/m2020\/wp-content\/uploads\/2020\/06\/image-35.png\")
<\/figure><\/div>\n\n\nPart 3 – Scene Manager<\/h3>\n\n\n\n
using UnityEngine.SceneManagement;<\/pre>\n\n\n\n
public void btn_StartTheGame()\n{\n SceneManager.LoadScene(\"TutorialLevel\");\n}<\/pre>\n\n\n\nPart 4 – Adding Scenes to the Build<\/h3>\n\n\n\n
![\"\"](\"https:\/\/courses.ideate.cmu.edu\/53-353\/m2021\/wp-content\/uploads\/2021\/06\/image-8.png\")
<\/figure><\/div>\n\n\nPart 5 \u2013 Staying Alive (DontDestroyMeBro!)<\/h3>\n\n\n\n
private void OnTriggerEnter2D(Collider2D collision)\n{\n if (collision.gameObject.tag == \"EndOfLevel\")\n {\n LevelManager.S.NextLevel();\n } \n}<\/pre>\n\n\n\npublic void NextLevel()\n{\n SceneManager.LoadScene(nextScene);\n}<\/pre>\n\n\n\n![\"\"](\"https:\/\/courses.ideate.cmu.edu\/53-353\/m2021\/wp-content\/uploads\/2021\/06\/image-9.png\")
DontDestroyOnLoad (this);\n<\/pre>\n\n\n\n
![\"\"](\"https:\/\/courses.ideate.cmu.edu\/53-353\/m2020\/wp-content\/uploads\/2021\/06\/image.png\")
![\"\"](\"https:\/\/courses.ideate.cmu.edu\/53-353\/m2020\/wp-content\/uploads\/2021\/06\/image-1.png\")
private void Awake()\n{\n if (S)\n {\n Destroy(this.gameObject); \n \/\/ Singleton already exists, remove this instance\n } else { \n S = this; \/\/ Singleton Definition\n }\n}<\/pre>\n\n\n\n![\"\"](\"https:\/\/courses.ideate.cmu.edu\/53-353\/m2020\/wp-content\/uploads\/2021\/06\/image-2.png\")
Part 6 – I’m Ready to Go Now<\/h3>\n\n\n\n
private void OnTriggerEnter2D(Collider2D collision)\n{\n if (collision.gameObject.tag == \"EndOfLevel\")\n {\n LevelManager.S.NextLevel();\n } else if (collision.gameObject.tag == \"EndOfGame\")\n {\n Debug.Log(\"EndOfGame Reached\");\n \/\/ tell the level manager to go back to the start menu\n LevelManager.S.GoToStartMenu();\n }\n}<\/pre>\n\n\n\nPart 7 – Restarting a Level<\/h3>\n\n\n\n
public void PlayerDied()\n{\n livesRemaining--;\n Debug.Log(\"Lives Remaining = \" + livesRemaining);\n\n if (livesRemaining <= 0)\n {\n LevelManager.S.GoToStartMenu();\n\n } else\n {\n LevelManager.S.RestartLevel();\n }\n}<\/pre>\n\n\n\npublic void RestartLevel()\n{\n SceneManager.LoadScene(SceneManager.GetActiveScene().name);\n}<\/pre>\n\n\n\n
\n\n\n\n
\n\n\n\nGameManager.cs<\/pre>\n\n\n\n
using System.Collections;\nusing System.Collections.Generic;\nusing UnityEngine;\nusing TMPro;\n\npublic class GameManager : MonoBehaviour\n{\n public string gameManagerName;\n\n private int score = 0;\n public TextMeshProUGUI scoreText;\n\n public static GameManager S; \/\/ singleton\n\n\n private int livesRemaining = 3;\n\n private void Awake()\n {\n if (S) {\n Destroy(this.gameObject);\n } else\n {\n S = this; \/\/ singleton definition\n }\n }\n\n \/\/ Start is called before the first frame update\n void Start()\n {\n DontDestroyOnLoad(this);\n }\n\n \/\/ Update is called once per frame\n void Update()\n {\n scoreText.text = \"Score: \" + score;\n }\n\n public void AddScore(int scoreValue)\n {\n score += scoreValue;\n }\n\n public void PlayerDied()\n {\n livesRemaining--;\n Debug.Log(\"Lives Remaining = \" + livesRemaining);\n\n if (livesRemaining <= 0)\n {\n LevelManager.S.GoToStartMenu();\n\n } else\n {\n LevelManager.S.RestartLevel();\n }\n }\n}\n<\/pre>\n\n\n\n
\n\n\n\nLevelManager.cs<\/pre>\n\n\n\n
using System.Collections;\nusing System.Collections.Generic;\nusing UnityEngine;\nusing UnityEngine.SceneManagement;\n\npublic class LevelManager : MonoBehaviour\n{\n public static LevelManager S; \/\/ singleton\n\n public string levelName;\n\n public string nextSceneName;\n\n\n private void Awake()\n {\n S = this;\n }\n\n \/\/ Start is called before the first frame update\n void Start()\n {\n \n }\n\n \/\/ Update is called once per frame\n void Update()\n {\n \n }\n\n public void btn_StartTheGame()\n {\n SceneManager.LoadScene(\"TutorialLevel\");\n\n }\n\n public void NextLevel()\n {\n SceneManager.LoadScene(nextSceneName);\n }\n\n public void GoToStartMenu()\n {\n SceneManager.LoadScene(0);\n Destroy(GameManager.S.gameObject);\n }\n\n public void RestartLevel()\n {\n SceneManager.LoadScene(SceneManager.GetActiveScene().name);\n }\n\n}\n<\/pre>\n\n\n\n
\n\n\n\nPlayerMovement.cs<\/pre>\n\n\n\n
using System.Collections;\nusing System.Collections.Generic;\nusing UnityEngine;\n\npublic class PlayerMovement : MonoBehaviour\n{\n private CharacterController2D controller;\n public float speed;\n\n private float horizontalMove = 0.0f;\n private bool jump = false;\n\n private Animator animator;\n\n \/\/ Start is called before the first frame update\n void Start()\n {\n controller = GetComponent<CharacterController2D>();\n animator = GetComponent<Animator>();\n }\n\n \/\/ Update is called once per frame\n void Update()\n {\n horizontalMove = Input.GetAxis(\"Horizontal\") * speed;\n\n if (Input.GetButtonDown(\"Jump\"))\n {\n jump = true;\n \/\/ set the jump\n animator.SetBool(\"isOnGround\", false);\n }\n\n \/\/ set the animator speed \n float ourSpeed = Input.GetAxis(\"Horizontal\");\n animator.SetFloat(\"speed\", Mathf.Abs(ourSpeed));\n\n }\n\n private void FixedUpdate()\n {\n controller.Move(horizontalMove * Time.fixedDeltaTime, false, jump);\n jump = false;\n }\n\n public void PlayerLanded()\n {\n \/\/ land the player\n animator.SetBool(\"isOnGround\", true);\n }\n\n private void OnCollisionEnter2D(Collision2D collision)\n {\n if (collision.gameObject.tag == \"Enemy\")\n {\n \/\/ player has died\n GetComponent<Rigidbody2D>().isKinematic = true;\n animator.SetTrigger(\"Death\");\n \n }\n }\n\n private void OnTriggerEnter2D(Collider2D collision)\n {\n if (collision.gameObject.tag == \"EndOfLevel\")\n {\n LevelManager.S.NextLevel();\n } else if (collision.gameObject.tag == \"EndOfGame\")\n {\n Debug.Log(\"EndOfGame Reached\");\n \/\/ tell the level manager to go back to the start menu\n LevelManager.S.GoToStartMenu();\n }\n }\n\n public void ProcessPlayerDeath()\n {\n GameManager.S.PlayerDied();\n }\n\n}\n<\/pre>\n\n\n\n
\n","protected":false},"excerpt":{"rendered":"