Tower Defense Tutorial - Fixing "Continue" Scene Errors

August 26, 2019

Tower Defense Tutorial Project

Fixing Scene Transition Between Levels When Continuing

I was able to clean up the scene management enough last time that going through the basic starting game scenes all worked well as far as I could tell. I could get from the main intro scene, to the level select screen, to level 1 without any issues. Progressing to level 2 was not working because of some reference with the enemy spawner object, so I will be looking into that.

PROBLEMS

PROBLEM #1

Level 2 does not load after playing Level 1 because of some reference issue for setting the spawn object.

The error was actually that spawnPoint in WaveInformation was not assigned, so I looked into that and saw that there was a public field for drag/dropping the spawn point object into that I just hadn't done in Level 2.

SOLUTION: Just setting this public field with the spawn point allowed the level to work properly.

General Testing

I edited Level 2 a bit more just to make sure the data was all being passed over to the WaveSpawner. I made sure to move the starting spawn point just in case that wasn't being updated and it just worked out visually since they were spawning from the same place as before. I also changed up the map layout and moved the waypoints around to fit this new layout. Running this updated level layout worked as expected, everything was properly updated when opening Level 2.

I had not tested using the Continue button from Level 1 since Level 2 was not working in any capacity until now, so I tried that now. This seemed to open Level 2 fine and ran the level, but it did not end when the last enemies were destroyed. I then tried using the pause menu to retry the level and this gave an error saying the SceneManager tried to SetActive an invalid scene.

Going to Level 2 from the level select menu seems to give no errors. The game ends with the player winning as expected, and the Retry and Menu options from the pause menu both work as intended. Something is being messed up when transferring directly from Level 1 to Level 2 with the Continue button function.

PROBLEM #2

Using the Next level option on the level complete screen is giving some errors. Most notably, the level complete screen does not come up on the next level when the player completes it, and using Retry on the level returns a scene error.

The Retry level error makes sense. The SceneManagerLite holds a reference to an int called currentLevelBuildIndex that is supposed to represent the scene index of the currently loaded level scene. This however is not being properly set when using the NextLevel method, so the RetryLevel method in SceneManagerLite refernces the currentLevelBuildIndex to determine which scene to load, and is actually seing the last level's index here. So what is happening is that it is loading the last level scene, then unloading it, and then trying to set it active. Since it is now unloaded, there is nothing to set active resulting in the error.

I believe the game not ending is as simple as the GameIsOver bool in the LevelManager not being reset. This is initialized on false, and set to true when the level does end. However, going straight from one level to the next never unloads the Base scene which contains the object holding the LevelManager, so that is never reset to false.

Test #1:

Two fold test: Properly set the currentLevelBuildIndex within the NextLevel method (in a way similar to the SelectLevel method); also reset the GameIsOver bool in LevelManager when using the NextLevel method.

Editing the NextLevel method in the SceneManagerLite was simple enough to just add setting the currentLevelBuildIndex to the proper value, but figuring out exactly where to reset the GameIsOver bool was a bit tricky. I wanted to place it somewhere where the reference to the LevelManager fit in cleanly, but it also needed to be somewhere that could set the value after calling a method like RetryLevel or NextLevel from the SceneManagerLite. (RetryLevel may be important for when the game ends from the player losing the level, or if we want to add a retry option even on completeing the current level). Setting it too early might cause issues where the game tried to end again while loading/unloading scenes.

SOLUTION 1: Setting the currentLevelBuildIndex in the NextLevel method of SceneManagerLite fixed problems loading the scene using NextLevel, as well as fixing the menu errors in game. Now using Retry and Menu after loading into a level with NextLevel work properly.

On the other end, I tried to fix the GameIsOver bool by creating a new script called LevelInitializer and placing it on to the LevelInformation object found in level scenes. This script simply attempts to get a reference to the LevelManager (which now has a static method and reference to be gotten) and ensure the LevelManager is properly reset when a level starts. This is done in the new LevelInitializer script's Start method, the thought here being that this should be called anytime a level scene is loaded, which is exactly when we want to ensure the LevelManager is reset. However, the game still was not ending after continuing from level 1 to 2.

Test #2:

I only needed to fix the second part of the problem now, and it seemed to be a rather easy fix. It turns out, since the LevelInformation object I added the LevelInitializer script to wasn't a prefab (it is now thanks to this issue), I only added LevelInitializer to Level 1. So Level 2 did not have this script at all, so it had no way to run the new reset method I created.

SOLUTION 2: I just needed to actually add the LevelInitializer script onto the LevelInformation object in every level scene. Doing this reset the LevelManager as intended so the player can now win when they use the Continue menu option on the level complete screen.

NEXT STEP

The scene management is almost completely finished and looking to work pretty well. The main process to test next will be losing conditions, since I have not checked that in a while. This may have a few kinks that I need to fix out since it has not been through the same testing as winning and progressins, but it should hopefully be some quick easy fixes if any.