Method RayCast

CollisionB2ShapePolygon.go:275–333

(output *B2RayCastOutput, input B2RayCastInput, xf B2Transform, childIndex int)

}

func (poly B2PolygonShape) RayCast(output *B2RayCastOutput, input B2RayCastInput, xf B2Transform, childIndex int) bool {

	// Put the ray into the polygon's frame of reference.
	p1 := B2RotVec2MulT(xf.Q, B2Vec2Sub(input.P1, xf.P))
	p2 := B2RotVec2MulT(xf.Q, B2Vec2Sub(input.P2, xf.P))
	d := B2Vec2Sub(p2, p1)

	lower := 0.0
	upper := input.MaxFraction

	index := -1

	for i := 0; i < poly.M_count; i++ {
		// p = p1 + a * d
		// dot(normal, p - v) = 0
		// dot(normal, p1 - v) + a * dot(normal, d) = 0
		numerator := B2Vec2Dot(poly.M_normals[i], B2Vec2Sub(poly.M_vertices[i], p1))
		denominator := B2Vec2Dot(poly.M_normals[i], d)

		if denominator == 0.0 {
			if numerator < 0.0 {
				return false
			}
		} else {
			// Note: we want this predicate without division:
			// lower < numerator / denominator, where denominator < 0
			// Since denominator < 0, we have to flip the inequality:
			// lower < numerator / denominator <==> denominator * lower > numerator.
			if denominator < 0.0 && numerator < lower*denominator {
				// Increase lower.
				// The segment enters this half-space.
				lower = numerator / denominator
				index = i
			} else if denominator > 0.0 && numerator < upper*denominator {
				// Decrease upper.
				// The segment exits this half-space.
				upper = numerator / denominator
			}
		}

		// The use of epsilon here causes the assert on lower to trip
		// in some cases. Apparently the use of epsilon was to make edge
		// shapes work, but now those are handled separately.
		//if (upper < lower - b2_epsilon)
		if upper < lower {
			return false
		}
	}

	B2Assert(0.0 <= lower && lower <= input.MaxFraction)

	if index >= 0 {
		output.Fraction = lower
		output.Normal = B2RotVec2Mul(xf.Q, poly.M_normals[index])
		return true
	}

	return false