Method RayCast

CollisionB2Collision.go:386–441

From Real-time Collision Detection, p179.

(output *B2RayCastOutput, input B2RayCastInput)

// From Real-time Collision Detection, p179.
func (bb B2AABB) RayCast(output *B2RayCastOutput, input B2RayCastInput) bool {
	tmin := -B2_maxFloat
	tmax := B2_maxFloat

	p := input.P1
	d := B2Vec2Sub(input.P2, input.P1)
	absD := B2Vec2Abs(d)

	normal := MakeB2Vec2(0, 0)

	for i := 0; i < 2; i++ {
		if absD.OperatorIndexGet(i) < B2_epsilon {
			// Parallel.
			if p.OperatorIndexGet(i) < bb.LowerBound.OperatorIndexGet(i) || bb.UpperBound.OperatorIndexGet(i) < p.OperatorIndexGet(i) {
				return false
			}
		} else {
			inv_d := 1.0 / d.OperatorIndexGet(i)
			t1 := (bb.LowerBound.OperatorIndexGet(i) - p.OperatorIndexGet(i)) * inv_d
			t2 := (bb.UpperBound.OperatorIndexGet(i) - p.OperatorIndexGet(i)) * inv_d

			// Sign of the normal vector.
			s := -1.0

			if t1 > t2 {
				t1, t2 = t2, t1
				s = 1.0
			}

			// Push the min up
			if t1 > tmin {
				normal.SetZero()
				normal.OperatorIndexSet(i, s)
				tmin = t1
			}

			// Pull the max down
			tmax = math.Min(tmax, t2)

			if tmin > tmax {
				return false
			}
		}
	}

	// Does the ray start inside the box?
	// Does the ray intersect beyond the max fraction?
	if tmin < 0.0 || input.MaxFraction < tmin {
		return false
	}

	// Intersection.
	output.Fraction = tmin
	output.Normal = normal
	return true
}

// Sutherland-Hodgman clipping.