🔥 How to Make a Game Like Lost War in Unity 6 | Full Beginner Tutorial (Step-by-Step) - Part 19

🎮 Unity OnTriggerEnter & OnTriggerExit Tutorial Explained | Why Trigger Functions Don’t Work Sometimes | Full Guide by TastyCherryGames 🍒


📘 What We’ll Learn Today

✅ Why OnTriggerEnter might not be called in Unity
✅ The difference between Collider and Trigger Collider
✅ How Unity handles collision detection vs trigger events
✅ What happens when your player passes through an object
✅ Enabling the “Is Trigger” option to fix issues
✅ Understanding OnTriggerEnter(), OnTriggerExit(), and OnTriggerStay()
✅ Logical flow of trigger detection
✅ Debugging tips to test trigger collisions properly
✅ How to set up your Unity scene for testing
✅ Preparing logic adjustments for your next coding session

🎬 Video Overview

In the previous tutorial, we set up two cubes as pass-through objects and placed a character in front of them. Now we’re asking an important question:

🧠 “What will happen if our character passes through one of these objects?”

Will the OnTriggerEnter() function be called?
Or will it not trigger at all?



🧩 The Core Concept – Colliders vs Triggers

By default, when you create a Cube in Unity, it automatically comes with a Box Collider component enabled.
This collider is used for physical interactions — like preventing one object from passing through another.


For trigger-based detection (where you want objects to overlap and trigger an event without colliding physically), you must enable the “Is Trigger” checkbox in the collider component.

When that’s checked, Unity treats the collider as a trigger zone — meaning it will detect overlaps but won’t block the player physically.

Without enabling this option, your OnTriggerEnter() function won’t get called — even though your object has a collider! ⚠️



Let’s recap what happened in the video:

⏯️ When we played the game, our character passed right through the cubes — but nothing appeared in the console.
That’s because both the left wall and right wall cubes didn’t have Is Trigger enabled.

Once we checked that option and hit play again,

🟢 “Started overlapping with Left Wall Q”
and later
🔴 “Trigger ended with Left Wall Q”

That confirmed our OnTriggerEnter() and OnTriggerExit() were finally working!

🔍 The Common Mistake

Many beginners forget that having a collider is not enough to trigger OnTriggerEnter.
It must have Is Trigger enabled, and your player or interacting object must also have a Rigidbody component (for physics-based detection).

This combination ensures Unity recognizes it as a valid trigger event scenario.

So, if your code isn’t firing,
✅ Is your collider set to “Is Trigger”?
✅ Does your moving object have a Rigidbody?
✅ Is the script properly attached to the GameObject with the trigger collider?

⚙️ Behind the Scenes:

When Unity’s physics engine runs, it classifies colliders into two categories:

Solid Colliders: Physical barriers that prevent penetration.

Trigger Colliders: Non-physical zones that fire events when overlapped.

If both colliders are solid, Unity handles them as collisions (using OnCollisionEnter instead of OnTriggerEnter).
If one of them is a trigger, it uses trigger-based detection (OnTriggerEnter, OnTriggerStay, OnTriggerExit).

This distinction is crucial for building portals, pickups, detection zones, checkpoints, and traps in your game.



You can find this in:
Edit → Project Settings → Physics → Layer Collision Matrix

🕹️ Real-World Uses of Triggers

Triggers are used everywhere in game development! Here are a few examples:

🎯 Detecting when a player picks up coins or power-ups
🚪 Opening doors automatically when a character walks near
⚡ Activating traps or hazards when a player enters a region
💥 Detecting bullet hits or explosion zones
🏁 Marking checkpoint zones for saving player progress
📦 Detecting when an item enters a container area
👾 Triggering enemy AI awareness or alarms
🎵 Starting background music or cutscenes
📸 Activating camera changes or post-processing effects
🏆 Tracking achievements or story progress

Triggers make your game feel alive by responding to player interactions in dynamic ways!

🧰 Troubleshooting Checklist

If triggers still don’t behave as expected:
✅ Check that both objects have colliders.
✅ Ensure at least one object has Is Trigger enabled.
✅ Ensure at least one object has a Rigidbody.
✅ Confirm there are no conflicting scripts disabling the collider.
✅ Test using Debug.Log to verify function calls.

🕒 Timestamps

00:00 – Introduction and Recap
00:04 – Revisiting the previous tutorial setup
00:22 – Thinking challenge: What happens when character passes through?
01:00 – Collider defaults explained
01:24 – Demonstrating cube collider behavior
02:01 – Testing without trigger enabled (no output)
02:45 – Enabling “Is Trigger” on both walls
03:06 – Successful detection of overlaps
03:28 – Understanding trigger exit behavior
03:53 – Why OnTriggerExit fires unexpectedly
04:07 – Preparing logic improvements for next tutorial
04:49 – Final thoughts and summary