Swept AABB Collisions C#

gistfile1.txt

        public static bool TestAABBSweep(Vector2 extents1, Vector2 centre1, Vector2 velocity1, Vector2 extents2, Vector2 centre2, Vector2 velocity2, out float t0, out float t1)
        {
            var aabb1 = new AABB(centre1, extents1);
            var aabb2 = new AABB(centre2, extents2);
            
            //Check if the boxes are currently overlapping
            if (aabb1.Overlaps(aabb2))
            {
                t0 = t1 = 0;
                return true;
            }

            //The problem is solved in A's frame of reference so get relative velocity (in normalized time)
            var relativeVelocity = velocity2 - velocity1;

            //First and last time of overlap along each axis
            var firstOverlapTime = new Vector2(float.MinValue);
            var lastOverlapTime = new Vector2(float.MaxValue);
            
            var overlapX = false;
            var overlapY = false;

            //Find the first possible times of overlap...
            if (relativeVelocity.X < 0)
            {
                if (aabb1.MinX < aabb2.MaxX)
                {
                    overlapX = true;
                    firstOverlapTime.X = (aabb1.MaxX - aabb2.MinX) / relativeVelocity.X;
                }
            }
            else if (relativeVelocity.X > 0)
            {
                if (aabb2.MinX < aabb1.MaxX)
                {
                    overlapX = true;
                    firstOverlapTime.X = (aabb1.MinX - aabb2.MaxX) / relativeVelocity.X;
                }
            }
            else if (aabb1.MinX <= aabb2.MaxX && aabb1.MaxX >= aabb2.MinX)
            {
                overlapX = true;
                firstOverlapTime.X = 0.0f;
                lastOverlapTime.X = 1.0f;
            }

            if (relativeVelocity.Y < 0)
            {
                if (aabb1.MinY < aabb2.MaxY)
                {
                    overlapY = true;
                    firstOverlapTime.Y = (aabb1.MaxY - aabb2.MinY) / relativeVelocity.Y;
                }
            }
            else if (relativeVelocity.Y > 0)
            {
                if (aabb2.MinY < aabb1.MaxY)
                {
                    overlapY = true;
                    firstOverlapTime.Y = (aabb1.MinY - aabb2.MaxY) / relativeVelocity.Y;
                }
            }
            else if (aabb1.MinY <= aabb2.MaxY && aabb1.MaxY >= aabb2.MinY)
            {
                overlapY = true;
                firstOverlapTime.Y = 0.0f;
                lastOverlapTime.Y = 1.0f;
            }

            //...and the last possible time of overlap
            if (aabb2.MaxX > aabb1.MinX && relativeVelocity.X < 0)
                lastOverlapTime.X = (aabb1.MinX - aabb2.MaxX) / relativeVelocity.X;
            else if (aabb1.MaxX > aabb2.MinX && relativeVelocity.X > 0)
                lastOverlapTime.X = (aabb1.MaxX - aabb2.MinX) / relativeVelocity.X;

            if (aabb2.MaxY > aabb1.MinY && relativeVelocity.Y < 0)
                lastOverlapTime.Y = (aabb1.MinY - aabb2.MaxY) / relativeVelocity.Y;
            else if (aabb1.MaxY > aabb2.MinY && relativeVelocity.Y > 0)
                lastOverlapTime.Y = (aabb1.MaxY - aabb2.MinY) / relativeVelocity.Y;

            if (overlapX == false || overlapY == false)
            {
                t0 = t1 = 0;
                return false;
            }

            //Possible first time of overlap is the largest of the axis values
            t0 = Math.Max(firstOverlapTime.X, firstOverlapTime.Y);

            //So then the possible last time of overlap is the smallest of the overlaps values
            t1 = Math.Min(lastOverlapTime.X, lastOverlapTime.Y);

            //They could have only collided if the first time of overlap occurred before the last time of overlap
            return t0 >= 0 && t0 <= 1 && t0 <= t1;
        }