void b2PolygonShape::Set()

in Box2D/Collision/Shapes/b2PolygonShape.cpp [120:216]

• 74 lines of code
• 18 McCabe index (conditional complexity)

void b2PolygonShape::Set(const b2Vec2* vertices, int32 count)
{
	b2Assert(3 <= count && count <= b2_maxPolygonVertices);
	if (count < 3)
	{
		SetAsBox(1.0f, 1.0f);
		return;
	}
	
	int32 n = b2Min(count, b2_maxPolygonVertices);

	// Copy vertices into local buffer
	b2Vec2 ps[b2_maxPolygonVertices];
	for (int32 i = 0; i < n; ++i)
	{
		ps[i] = vertices[i];
	}

	// Create the convex hull using the Gift wrapping algorithm
	// http://en.wikipedia.org/wiki/Gift_wrapping_algorithm

	// Find the right most point on the hull
	int32 i0 = 0;
	float32 x0 = ps[0].x;
	for (int32 i = 1; i < count; ++i)
	{
		float32 x = ps[i].x;
		if (x > x0 || (x == x0 && ps[i].y < ps[i0].y))
		{
			i0 = i;
			x0 = x;
		}
	}

	int32 hull[b2_maxPolygonVertices];
	int32 m = 0;
	int32 ih = i0;

	for (;;)
	{
		hull[m] = ih;

		int32 ie = 0;
		for (int32 j = 1; j < n; ++j)
		{
			if (ie == ih)
			{
				ie = j;
				continue;
			}

			b2Vec2 r = ps[ie] - ps[hull[m]];
			b2Vec2 v = ps[j] - ps[hull[m]];
			float32 c = b2Cross(r, v);
			if (c < 0.0f)
			{
				ie = j;
			}

			// Collinearity check
			if (c == 0.0f && v.LengthSquared() > r.LengthSquared())
			{
				ie = j;
			}
		}

		++m;
		ih = ie;

		if (ie == i0)
		{
			break;
		}
	}
	
	m_count = m;

	// Copy vertices.
	for (int32 i = 0; i < m; ++i)
	{
		m_vertices[i] = ps[hull[i]];
	}

	// Compute normals. Ensure the edges have non-zero length.
	for (int32 i = 0; i < m; ++i)
	{
		int32 i1 = i;
		int32 i2 = i + 1 < m ? i + 1 : 0;
		b2Vec2 edge = m_vertices[i2] - m_vertices[i1];
		b2Assert(edge.LengthSquared() > b2_epsilon * b2_epsilon);
		m_normals[i] = b2Cross(edge, 1.0f);
		m_normals[i].Normalize();
	}

	// Compute the polygon centroid.
	m_centroid = ComputeCentroid(m_vertices, m);
}