Handling Player Vehicle Collision Detection In Unity

Detecting Vehicle Collisions

Defining collision layers and tags for vehicles and environment objects is an essential first step for collision detection. These allow efficient filtering so that vehicles only detect collisions with certain objects. Attach collider and rigidbody components to vehicle and object gameobjects to enable Unity’s physics engine to detect and respond to collisions.

Box colliders approximate a vehicle’s shape to detect collisions while rigidbodies allow the vehicle to interact realistically with physics forces. Configure the rigidbody’s collision detection mode to continuous or discrete for specific tradeoffs between accuracy and performance. Finally, implement the OnCollisionEnter callback to trigger custom logic when collisions occur.

Define Collision Layers and Tags

Collision layers provide a filtering mechanism to specify which objects can collide with each other. For a vehicle, typical layers include “Player”, “Enemy”, “Environment”, etc. Similarly, collision tags classify objects with string labels like “Obstacle” or “Powerup”.

First, define layers under Edit > Project Settings > Physics to create categorical divisions. Then assign vehicle and object gameobjects appropriate layers and tags based on their collision needs.

Attach Colliders and Rigidbodies

Physical colliders define an object’s shape for collision detection. Simple primitives like box, sphere or capsule colliders approximate most vehicles. Mesh colliders can model more complex shapes. Attach colliders efficiently sized to vehicles to balance accuracy and performance.

Additionally, rigidbodies handle physics interactions, allowing vehicles to move realistically. Vehicles require rigidbodies set to specific modes like “Kinematic” for direct motion control. Configure mass, drag and collision detection to produce desired movement when collisions occur.

Configure Collision Detection Settings

The rigidbody’s Collision Detection Mode impacts physics performance and accuracy. The “Discrete” mode detects fast-moving collisions between fixed timestep updates while “Continuous” dynamically casts colliders every frame, improving accuracy but with a performance cost.

Other relevant settings include Collision Detection quality, solver iteration count, and constraints. Tune these variables to balance realistic vehicle collision behavior with efficient performance for your projects.

Use OnCollisionEnter Callback

The OnCollisionEnter method sends a callback when a collision first occurs between two objects with configured colliders/rigidbodies. Within this function, get references to both collision gameobjects using Collision.gameObject and Collision.contacts to access specific collision details.

This allows executing custom vehicle collision logic like applying physics forces, triggering particle effects, modifying stats, or playing audio. Useful information includes collision impulse, contact point normal, and relative velocity of the collision.

Determining Collision Details

When a vehicle collision occurs, key details like the objects involved, speed/force, contact zone, and direction help determine appropriate responses. Get references to colliding gameobjects and extract their unity layer, tag, and other component information to identify vehicle vs environment objects.

Use impulse and relative velocity of collision contacts to gauge force. Cycle through all contact points to determine the collision surface normal and locate which part of the vehicle was hit. These details feed into spawning impact effects and modifying vehicle states.

Get References to Colliding Gameobjects

Within OnCollisionEnter, the Collision parameter provides the other Collider’s GameObject reference via Collision.gameObject. With this, use GetComponent to access necessary components like attached Rigidbody, VehicleController script, Collider shapes, etc.

These references allow checking object tags/layers, parent-child hierarchies, executing public component methods, and meeting other collision response needs.

Check Tags/Layers of Colliding Objects

A vehicle may collide with many types of gameobjects. Use Unity tags and layers to categorize them, e.g. environment objects as “Obstacles” on the “Level” layer. When a collision occurs, check Collision.gameObject layer and tag properties to verify object types.

For example, apply extra collision force for objects tagged “Powerup” or ignore collisions completely with ones assigned to “NoCollision” layer. This filters appropriate responses.

Calculate Impulse/Force of Collision

The impulse applied to the vehicle helps determine collision consequences. Get the accumulated impulse via Collision.impulse, calculate individual contact point impulses, or integrate Collision.relativeVelocity over time to approximate force intensity.

Alternatively, trigger effects based on Collision.relativeVelocity magnitude directly. Inspect variables like Rigidbody.velocityChange to help calculate force vectors.

Use the derived intensity variables to spawn proportional particle systems, apply physics impulses, deduct health percentages, or inform audio pitch/volumes.

Determine Collision Side/Location

Cycle through Collision.contacts array to gather details on all contact points. The ContactPoint normal establishes collision direction, while position indicates the surface area hit.

For example, a front collision normal points towards the vehicle with a lower position.y value. Calculate averages over all contacts to approximate the impact zone and side.

This distinction helps spawn appropriate damage effects to vehicle sections. Front collisions might reduce health and speed while a side collision could apply a spin impulse.

Responding to Collisions

With collision details available, game logic can execute appropriate effects. Use sound and particle systems to convey impact intensity through volume and quantity. Apply physics impulses for knockback effects.

Modify vehicle properties like health, speed stats to represent damage. Detect collisions with special trigger colliders to initiate power-ups, explosions or other gameplay outcomes not dependent on physics.

Play Sound Effects

Collision audio feedback adds realism and satisfaction. Simple collision triggers can enable single sound effects on impact. For more depth, use collision details to drive parameters.

Increase audio source volume and pitch based on collision force. Randomize SFX clips selected from an array to add variety over multiple impacts. Finally, set oneshot clips on the colliding objects themselves for spatialized sound.

Create Particle Effects

Visual fx like sparks, smoke, and debris help sell the collision intensity. Spawn one-shot particle systems on contact points or as children of vehicle objects to move along.

Scale emission rates and lifetimes based on characteristics like Collision.relativeVelocity for proportional intensity. Emit in the collision normal direction to align particles with the impact zone.

Apply Physics Impulses

For realistic vehicle reactions, directly manipulate rigidbody physics with scripts. Impulses like Collision.impulse produce instant velocity changes while AddForce applies sustained acceleration.

Raycast vehicle controllers allow modifying torque/power for spinouts. Integrate velocity changes over time to mimic mass displacement. Enable engine simulation for RPMS-based torque math.

This physics manipulation paired with vehicle sound and visual effects heightens realism following collisions.

Modify Vehicle Properties

Aside from direct physics reactions, update internal vehicle state from impacts. Reduce structural integrity points representing “health” based on collision magnitude to eventually destroy the vehicle.

Tune friction curves on vehicle controllers to simulate loose components or disabled wheels. Increase mass properties over time from accumulated debris. Reset power levels on electric vehicles to represent battery drainage.

This ties collision consequences to overall gameplay progression beyond the immediate physics simulation.

Check for Trigger Volumes

In special gameplay scenarios, detect collisions with invisible trigger colliders without associated rigidbodies. For example, initiate explosions when colliding with a mine trigger volume.

Or use triggers to detect entry into a powerup volume for temporarily boosting vehicle capabilities. No actual physics reaction occurs but game logic still executes.

This provides additional flexibility over just rigidbody collisions in designing gameplay systems.

Optimizing Collision Performance

Complex games with many colliding objects and vehicles require optimized configurations for efficient performance. Fortunately, various collision detection settings, physics modification and general best practices help.

Use discrete mode for fewer overall checks at a physics cost. Reduce collider complexity with simpler primitives over high polygon meshes when possible. Filter contacts between objects that don’t need per-frame updates.

Finally, object pooling minimizes allocation / deallocation from one-shot effects by reusing instantiated elements.

Use Discrete Collision Detection

The Discrete Collision Detection setting makes the physics engine evaluate collisions only at fixed intervals instead of continuously. This reduces overall checks for better performance at the cost of less accuracy.

Discrete mode works best for fast vehicles that move large distances within a single physics update. Fine-tune the Physics.stepsPerSecond to check more/less frequently if needed.

Adjust Physics Steps Per Frame

The fixed timestep Physics.fixedDeltaTime controls how frequently the physics engine updates per frame. The default 50 Hz works for most games but faster updates like 100+ Hz better handle fast vehicles at the expense of processing.

For slower gameplay, reduced steps like 30 Hz minimizes computation. Find the optimal balance through testing for your vehicle top speeds and device capabilities.

Simplify Collider and Rigidbody Shapes

Complex mesh colliders with many vertices are accurate for collision but inefficient to check. Simplify vehicles with approximated primitive shapes like boxes, spheres and capsules when reasonable.

Similarly, setting rigidbodies to kinematic or static when objects don’t move reduces processing. Enable only when necessary for active vehicles.

Filter Collision Contacts

The Collision Matrix panel under Physics Settings allows disabling contacts between specific gameobject layers, keeping vehicles from processing unnecessary collisions.

For example, ignore trigger volumes or distant background objects. Selective ignoring optimizes scene queries so vehicles detect only relevant objects.

Pool Collision Effect Objects

Spawned particles, sound clips and other collision effects are often one-shot elements enabled briefly before destruction. This churn allocates and deallocates substantial memory.

Instead, pool pre-loaded effect objects to instantiate copies from on collision, disabling them once finished for later reuse without destroying. This avoids repeated memory churn.

Example Collision Detection Script

This script demonstrates detecting a vehicle collision within a trigger volume, extracting key details like contact impulse and reacting with sound effects and debug logs.

Attach to vehicle with appropriate layer setup. Edit public fields to set collision sound clips, volume levels, etc. View debug logs for contact specifics on collisions.

Show Commented Code Sample

//Existence implies attached to vehicle gameobject
public class VehicleCollisionDetector : MonoBehaviour {

    //Adjust to preferred layers
    public LayerMask collisionMask;  

    public AudioClip[] crashClips;

    void OnCollisionEnter(Collision col) {
    
        //Only detect collisions with trigger volumes   
        if(col.gameObject.layer == LayerMask.NameToLayer("Trigger")) {

            //Get impulse force of collision
            float impactSpeed = col.impulse.magnitude;    

            //Calculate volume based on speed 
            float volume = Mathf.Clamp01(impactSpeed / 10.0f)

            //Pick random clip to play
            int randomIndex = Random.Range(0, crashClips.Length);
                
            AudioSource.PlayClipAtPoint(crashClips[randomIndex], transform.position, volume);

            //Print contact details 
            foreach(ContactPoint contact in col.contacts) {
                Debug.Log("Contact Point Details: " + contact.point + ", " + contact.normal + ", Relative Velocity: " + contact.relativeVelocity);
            }   
        }
    }
}  

Detect Collision with Trigger Volume

Check for a collision between the player vehicle layer and objects set to trigger volumes using bitmask layers instead of comparing string tags.

Triggers with no rigidbody allow collision callbacks without physics reactions – perfect for entering special areas.

Get Collision Impulse and Print

The ContactPoint includes useful collision details like impulse magnitude and relative velocity used here to parameterize sound volume.

Printing all ContactPoint data logs the actual collision direction, location, and force data.

Play Collision Sound Effect

Randomly choose a crash sound clip to add variety on each collision.

Use the calculated impulse speed to drive sound volume for proportional intensity based on collision force.