bool b2PolygonShape::RayCast()

in Box2D/Collision/Shapes/b2PolygonShape.cpp [234:304]
46 lines of code
11 McCabe index (conditional complexity)

bool b2PolygonShape::RayCast(b2RayCastOutput* output, const b2RayCastInput& input,
								const b2Transform& xf, int32 childIndex) const
{
	B2_NOT_USED(childIndex);

	// Put the ray into the polygon's frame of reference.
	b2Vec2 p1 = b2MulT(xf.q, input.p1 - xf.p);
	b2Vec2 p2 = b2MulT(xf.q, input.p2 - xf.p);
	b2Vec2 d = p2 - p1;

	float32 lower = 0.0f, upper = input.maxFraction;

	int32 index = -1;

	for (int32 i = 0; i < m_count; ++i)
	{
		// p = p1 + a * d
		// dot(normal, p - v) = 0
		// dot(normal, p1 - v) + a * dot(normal, d) = 0
		float32 numerator = b2Dot(m_normals[i], m_vertices[i] - p1);
		float32 denominator = b2Dot(m_normals[i], d);

		if (denominator == 0.0f)
		{	
			if (numerator < 0.0f)
			{
				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 < 0.0f && numerator < lower * denominator)
			{
				// Increase lower.
				// The segment enters this half-space.
				lower = numerator / denominator;
				index = i;
			}
			else if (denominator > 0.0f && 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(0.0f <= lower && lower <= input.maxFraction);

	if (index >= 0)
	{
		output->fraction = lower;
		output->normal = b2Mul(xf.q, m_normals[index]);
		return true;
	}

	return false;
}