Collision Avoidance using Raycasts in C# Code Snippet


I just add some pretty good code for collision avoidance in Space Warfare… Most code ideas I found around the nets about collision avoidance use the same block of Unity Javascript. Well, Javascript is taking a back seat in Unity pretty soon and I don’t really use it. I thought other folks might like the same code snippet in C#. Here it is!


//subtract AI thing’s position from waypoint, player, whatever it is going towards…

Vector3 target = targetYouAreFollowing.position – transform.position;

//normalize it to get direction
target = target.normalized;

//now make a new raycast hit
//and draw a line from the AI out some distance in the ‘forward direction

RaycastHit hit;

if(Physics.Raycast(transform.position, transform.forward, out hit, 800f)){

//check that its not hitting itself
//then add the normalised hit direction to your direction plus some repulsion force -in my case // 400f

if(hit.transform != transform){
Debug.DrawLine(transform.position, hit.point,;

target +=hit.normal * 400f;


//now make two more raycasts out to the left and right to make the cornering more accurate and reducing collisions more

Vector3 leftR = transform.position;
Vector3 rightR = transform.position;

leftR.x -= 2;
rightR.x +=2;

if(Physics.Raycast(leftR, transform.forward, out hit, 800f)){
if(hit.transform != transform){
Debug.DrawLine(leftR, hit.point,;
target +=hit.normal * 400f;

if(Physics.Raycast(rightR, transform.forward, out hit, 800f)){
if(hit.transform != transform){
Debug.DrawLine(rightR, hit.point,;

target +=hit.normal * 400f;


// then set the look rotation toward this new target based on the collisions

Quaternion torotation = Quaternion.LookRotation(target);

//then slerp the rotation
transform.rotation = Quaternion.Slerp(transform.rotation, torotation, Time.deltaTime * 100f);

//finally add some propulsion to move the object forward based on this rotation
//mine is a little more complicated than below but you hopefully get the idea…

transform.position += transform.forward *20f *Time.deltaTime;


Thanks to and for explaining the concept to me. If any readers are having trouble, check those sources… My numbers for distance and repulsion are based on spaceship moving at high speeds. The examples show slow moving spheres so their numbers might work better.

Next I will be adding a case where if all three raycasts hit you need to move one way or another. Otherwise, everything cancels out just about and ships still crash into stuff and explode. I kinda want that to happen a little bit so that you can feel like you are in a good asteroid chase scene, but not so much that it is over in seconds…