Circle-to-circle collision with Collider.Cast

Hey everyone!

I'm trying to handle circle-to-circle collision with the use of collider.Cast and it got it working properly. But as soon as I have an offset to my collider (either with the transform component, or the offset values on the collider) it goes wrong.

I've tried experimenting with lots of different things, but none seem to do the trick. I have a gif showing the issue here:



The code for the circle displacement calculations is this:

Code (CSharp):

1.     public static Vector2 CalculateCircleDisplacement(CircleCollider2D displacementCircle, CircleCollider2D otherCircle)
2.     {
3.         float displacementPosX = displacementCircle.transform.position.x + displacementCircle.offset.x;
4.         float displacementPosY = displacementCircle.transform.position.y + displacementCircle.offset.y;
5.  
6.         float otherPosX = otherCircle.transform.position.x + otherCircle.offset.x;
7.         float otherPosY = otherCircle.transform.position.y + otherCircle.offset.y;
8.  
9.         float distanceX = displacementPosX - otherPosX;
10.         float distanceY = displacementPosY - otherPosY;
11.  
12.         float sumRadius = displacementCircle.radius + otherCircle.radius;
13.  
14.         float length = Mathf.Sqrt(distanceX * distanceX + distanceY * distanceY);
15.  
16.         if (length == 0.0f)
17.         {
18.             length = 1.0f;
19.         }
20.  
21.         float unitX = distanceX / length;
22.         float unitY = distanceY / length;
23.  
24.         return new Vector2(otherPosX + (sumRadius) * unitX,
25.             otherPosY + (sumRadius) * unitY);
26.     }

Here is the movement code:

Code (CSharp):

1.     private void InternalMove(Vector2 movement)
2.     {
3.         if (settings.DynamicObstacleCollision)
4.         {
5.             if (ColliderCast(movement * Time.fixedDeltaTime, dynamicObstacleFilter, out RaycastHit2D hit))
6.             {
7.                 Vector2 displacement = PhysicsUtils.CalculateCircleDisplacement(bodyCollider, hit.collider as CircleCollider2D);
8.  
9.                 if (showDebug)
10.                 {
11.                     Debug.DrawRay(bodyCollider.transform.position, displacement + movement * Time.fixedDeltaTime, Color.cyan);
12.                 }
13.  
14.                 body.MovePosition(displacement + movement * Time.fixedDeltaTime);
15.                 return;
16.             }
17.         }
18.  
19.         body.MovePosition(body.position + movement * Time.fixedDeltaTime);
20.     }

Also to note, the ColliderCast function works even when the collider is offset. So it has to be something inside the CalculateCircleDisplacement method I would say. But this is the ColliderCast code:

Code (CSharp):

1.     public bool ColliderCast(Vector2 direction, ContactFilter2D filter, out RaycastHit2D hit, Collider2D collider = null)
2.     {
3.         if (collider == null)
4.         {
5.             collider = bodyCollider;
6.         }
7.  
8.         RaycastHit2D[] colliderCastHits = new RaycastHit2D[10];
9.         int numHits = collider.Cast(direction, filter, colliderCastHits, direction.magnitude);
10.  
11.         if (numHits > 0)
12.         {
13.             hit = colliderCastHits[0];
14.             return true;
15.  
16.             float dot = Vector2.Dot(direction.normalized, (hit.transform.position - bodyCollider.transform.position).normalized);
17.             if (dot > 0.0f)
18.             {
19.                 return true;
20.             }
21.         }
22.  
23.         //No collision
24.         hit = new RaycastHit2D();
25.         return false;
26.     }

The movement code is of course run in FixedUpdate.
Any help would gladly be appreciated!

 

Hey, thanks for the very thorough explanation! A lot of stuff I need to tweak and rework I can see.

But, I tried replacing my line of code with yours like this:

Code (CSharp):

1.     private void InternalMove(Vector2 movement)
2.     {
3.         if (settings.DynamicObstacleCollision)
4.         {
5.             if (ColliderCast(movement * Time.fixedDeltaTime, dynamicObstacleFilter, out RaycastHit2D hit))
6.             {
7.                 body.MovePosition(body.position + movement * Time.fixedDeltaTime * hit.fraction);
8.                 return;
9.             }
10.         }
11.  
12.         body.MovePosition(body.position + movement * Time.fixedDeltaTime);
13.     }

That unfortunately didn't work either. Now the "player" circle is just stuck whenever it interacts with the other one:


In regards to this not working with other physics shapes is fine, because all of my units are gonna have circle colliders. The dot product check was mostly just to not collide when the movement is in the opposite direction of the colliders.

Basically what I'm trying to accomplish is getting that "sliding" behaviour when I move directly into the circle.

 

Alright, thanks MelvMay! I'm gonna give those options a try. I got it working currently with the dot product check, but no sliding is occuring because of that. Gonna have to investigate on how to move the body correctly to get the sliding effect.

 

Amazing! Thank you so much for your help! Gonna have a go through that :-D

 

Hey MelvMay!

Thanks for your code. I got a version of a kinematic character controller working in my game now which is awesome.

Now, I'm trying to convert our old "Dodge Roll" code to this new code and I'm having trouble seeing if this is possible with how it's implemented. Previously, we just used the Rigidbody2D.MovePosition(dodgePos), and the dodge pos was fed into the function from an animation curve with a start and end position. This way we would have control over the whole dodge and the easing.

But with this new way (movement logic is pretty much the same as your github example), if we just use MovePosition, we lose the collision logic. I'm having difficulty thinking of a way to have the same control over my dodge roll, but still have the collision as well.

Movement Logic:

Code (CSharp):

1.     private void InternalMove(Vector2 movement)
2.     {
3.         if (movement.sqrMagnitude <= EPSILON)
4.         {
5.             return;
6.         }
7.  
8.         Vector2 startPos = body.position;
9.         Vector2 moveDirection = movement.normalized;
10.  
11.         float distanceRemaining = movement.magnitude * Time.fixedDeltaTime;
12.         int currentIterations = settings.MaxIterations;
13.  
14.         while (currentIterations-- > 0 && distanceRemaining > EPSILON && moveDirection.sqrMagnitude > EPSILON)
15.         {
16.             float distance = distanceRemaining;
17.  
18.             int hitCount = bodyCollider.Cast(moveDirection, settings.MovementFilter, movementHits, distance);
19.  
20.             if (hitCount > 0)
21.             {
22.                 RaycastHit2D hit = movementHits[0];
23.                 ColliderDistance2D colliderDistance = Physics2D.Distance(bodyCollider, hit.collider);
24.  
25.                 if (hit.distance > settings.ContactOffset)
26.                 {
27.                     distance = hit.distance - settings.ContactOffset;
28.                     body.position += moveDirection * distance;
29.                 }
30.                 else if (colliderDistance.isOverlapped)
31.                 {
32.                     distance = colliderDistance.distance;
33.                     body.position += colliderDistance.normal * colliderDistance.distance;
34.                 }
35.                 else
36.                 {
37.                     distance = 0.0f;
38.                 }
39.  
40.                 moveDirection -= hit.normal * Vector2.Dot(moveDirection, hit.normal);
41.             }
42.             else
43.             {
44.                 body.position += moveDirection * distance;
45.             }
46.  
47.             distanceRemaining -= distance;
48.         }
49.  
50.         Vector2 targetPosition = body.position;
51.         body.position = startPos;
52.  
53.         body.MovePosition(targetPosition);
54.     }
55.  
56.     public void SetPosition(Vector2 position)
57.     {
58.         body.MovePosition(position);
59.     }

Dodge Logic:

Code (CSharp):

1.     private IEnumerator IEDash(Vector2 direction, DashSettings settings)
2.     {
3.         dashing = true;
4.  
5.         float timer = 0.0f;
6.         float t;
7.  
8.         Vector2 startPos = body.GetPosition();
9.         Vector2 endPos = startPos + direction.normalized * settings.Distance;
10.  
11.         IMDraw.Line3D(startPos, endPos, Color.yellow, settings.Duration);
12.  
13.         while (timer < settings.Duration)
14.         {
15.             t = settings.Curve.Evaluate(timer / settings.Duration);
16.             Vector2 tPos = Vector2.Lerp(startPos, endPos, t);
17.  
18.             body.SetPosition(tPos);
19.             IMDraw.WireBox3D(tPos, Vector3.one * 0.2f, Color.yellow);
20.  
21.             timer += Time.deltaTime;
22.             yield return null;
23.         }
24.  
25.         //while (timer < settings.Duration)
26.         //{
27.         //    t = settings.Curve.Evaluate(timer / settings.Duration);
28.  
29.         //    Vector2 tPos = Vector2.Lerp(startPos, endPos, t);
30.         //    Vector2 moveDir = tPos - previousPos;
31.  
32.         //    body.Move(moveDir.normalized * 5.0f);
33.  
34.         //    previousPos = tPos;
35.  
36.         //    timer += Time.deltaTime;
37.         //    yield return null;
38.         //}
39.  
40.         dashing = false;
41.         unit.Input.ActivateAllActions(true);
42.         unit.StateMachineController.StateMachine.ChangeState(UnitStates.UnitState.Idle);
43.     }

As you can see, I've also tried with calling Move (which just sets the movement variable that the body uses) from the direction based on current and previous position, but with no luck.

Any pointers on how to handle this?

 

Sorry, I'll try to be more specific.

So, this is a gif of how our dodge roll looks like in-game, working with the code from above:



EDIT: gif dead for some reason? Here's the link: https://i.imgur.com/2SpN1LP.gif

As you can see, no collision is happening because we are just calling the "body.SetPosition(tPos)" on line 18 in the IEDash() IEnumerator.

Do you have any guidance on how we would achieve this same dodge roll, with our custom animation curve, and still have collisions?
Because it seems to me, that when we want that control over our dodge roll, from an animation curve, we have to "break" the physics and set the position directly.

I hope that helped clear up some of the confusion.

 

Haha, I guess I'm just very bad at explaining myself

So, the problem is that the InternalMove method, where all the collision stuff is happening, is passed in a movement vector. A direction, basically.

But when I'm using the IEDash IEnumerator, I'm settings the position directly, meaning I can't use the InternalMove where all the collision checks are.
So I guess my question is just how I would go on about checking for collision, when I'm setting the position directly. The only thing I've thought of is comparing the new position passed in, to the body's current position and check for overlaps etc.

EDIT: The rigidbody has the same settings as yours (bodyType is kinematic, useFullKinematicContacts).
The InternalMove is called with FixedUpdate(), but you're correct the SetPosition() is called from a coroutine which runs in Update I guess.

 

Okay, so I tried implementing the same collision logic as in the InternalMove (just for testing) and that gave me this result:


( https://i.imgur.com/i4sfoOu.gif )

With the code:

Code (CSharp):

1.     private IEnumerator IEDash(Vector2 direction, DashSettings settings)
2.     {
3.         dashing = true;
4.  
5.         float timer = 0.0f;
6.         float t;
7.  
8.         Vector2 startPos = body.GetPosition();
9.         Vector2 endPos = startPos + direction.normalized * settings.Distance;
10.  
11.         IMDraw.Line3D(startPos, endPos, Color.yellow, settings.Duration);
12.  
13.         while (timer < settings.Duration)
14.         {
15.             t = settings.Curve.Evaluate(timer / settings.Duration);
16.             Vector2 tPos = Vector2.Lerp(startPos, endPos, t);
17.  
18.             body.SetPosition(tPos);
19.             IMDraw.WireBox3D(tPos, Vector3.one * 0.2f, Color.yellow);
20.  
21.             timer += Time.deltaTime;
22.             yield return null;
23.         }
24.  
25.         dashing = false;
26.     }

Code (CSharp):

1. public void SetPosition(Vector2 position)
2.     {
3.         Vector2 move = position - body.position;
4.  
5.         IMDraw.WireSphere3D(body.position, bodyCollider.radius, Color.yellow);
6.  
7.         Vector2 startPos = body.position;
8.         Vector2 moveDirection = move.normalized;
9.  
10.         float distanceRemaining = move.magnitude;
11.         int currentIterations = settings.MaxIterations;
12.  
13.         while (currentIterations-- > 0 && distanceRemaining > EPSILON && moveDirection.sqrMagnitude > EPSILON)
14.         {
15.             float distance = distanceRemaining;
16.  
17.             int hitCount = bodyCollider.Cast(moveDirection, settings.MovementFilter, movementHits, distance);
18.  
19.             if (hitCount > 0)
20.             {
21.                 RaycastHit2D hit = movementHits[0];
22.                 ColliderDistance2D colliderDistance = Physics2D.Distance(bodyCollider, hit.collider);
23.  
24.                 if (hit.distance > settings.ContactOffset)
25.                 {
26.                     distance = hit.distance - settings.ContactOffset;
27.                     body.position += moveDirection * distance;
28.                 }
29.                 else if (colliderDistance.isOverlapped)
30.                 {
31.                     distance = colliderDistance.distance;
32.                     body.position += colliderDistance.normal * colliderDistance.distance;
33.                 }
34.                 else
35.                 {
36.                     distance = 0.0f;
37.                 }
38.  
39.                 moveDirection -= hit.normal * Vector2.Dot(moveDirection, hit.normal);
40.                 IMDraw.WireSphere3D(position, bodyCollider.radius, Color.red);
41.  
42.             }
43.             else
44.             {
45.                 body.position += moveDirection * distance;
46.                 IMDraw.WireSphere3D(position, bodyCollider.radius, Color.blue);
47.             }
48.  
49.             distanceRemaining -= distance;
50.         }
51.  
52.         Vector2 targetPosition = body.position;
53.         body.position = startPos;
54.  
55.         body.MovePosition(targetPosition);
56.     }

As you can see, the character snaps around corners, because it's just trying to set the next position between the start and end of the dodge.

I don't have much clue on how to handle this, while still maintaining the "slidyness" when collider with walls etc.

 

Just wanted to say I got it fixed the way I wanted! I'm handling the dodge roll now with the same movement code as before, just with previous position and current position as actual movement.

Thanks again MelvMay.