public void ComputeCentroidToOut(Vec2[] vs, int count, Vec2 result) { Debug.Assert(count >= 3); result.Set(0.0f, 0.0f); float area = 0.0f; // pRef is the reference point for forming triangles. // It's location doesn't change the result (except for rounding error). Vec2 pRef = pool1; pRef.SetZero(); Vec2 e1 = pool2; Vec2 e2 = pool3; const float inv3 = 1.0f / 3.0f; for (int i = 0; i < count; ++i) { // Triangle vertices. Vec2 p1 = pRef; Vec2 p2 = vs[i]; Vec2 p3 = i + 1 < count ? vs[i + 1] : vs[0]; e1.Set(p2).SubLocal(p1); e2.Set(p3).SubLocal(p1); float D = Vec2.Cross(e1, e2); float triangleArea = 0.5f * D; area += triangleArea; // Area weighted centroid e1.Set(p1).AddLocal(p2).AddLocal(p3).MulLocal(triangleArea * inv3); result.AddLocal(e1); } // Centroid Debug.Assert(area > Settings.EPSILON); result.MulLocal(1.0f / area); }
/// <seealso cref="Joint.GetReactionForce(float, Vec2)"></seealso> public override void GetReactionForce(float inv_dt, Vec2 argOut) { argOut.Set(m_impulse.X, m_impulse.Y); argOut.MulLocal(inv_dt); }