```//----------------------------------------------------------------------- // // Copyright (c) Microsoft Corporation. All rights reserved. // //----------------------------------------------------------------------- using System; using System.Windows; using System.Windows.Media; using System.Collections; using System.Collections.Generic; using System.Collections.ObjectModel; using MS.Utility; using SR=MS.Internal.PresentationCore.SR; using SRID=MS.Internal.PresentationCore.SRID; namespace MS.Internal.Ink { /// /// A helper structure used in StrokeNode and StrokeNodeOperation implementations /// to store endpoints of the quad connecting two nodes of a stroke. /// The vertices of a quad are supposed to be clockwise with points A and D located /// on the begin node and B and C on the end one. /// internal struct Quad { #region Statics private static Quad s_empty = new Quad(new Point(0, 0), new Point(0, 0), new Point(0, 0), new Point(0, 0)); #endregion #region API /// Returns the static object representing an empty (unitialized) quad internal static Quad Empty { get { return s_empty; } } /// Constructor internal Quad(Point a, Point b, Point c, Point d) { _A = a; _B = b; _C = c; _D = d; } /// The A vertex of the quad internal Point A { get { return _A; } set { _A = value; } } /// The B vertex of the quad internal Point B { get { return _B; } set { _B = value; } } /// The C vertex of the quad internal Point C { get { return _C; } set { _C = value; } } /// The D vertex of the quad internal Point D { get { return _D; } set { _D = value; } } // Returns quad's vertex by index where A is of the index 0, B - is 1, etc internal Point this[int index] { get { switch (index) { case 0: return _A; case 1: return _B; case 2: return _C; case 3: return _D; default: throw new IndexOutOfRangeException("index"); } } } /// Tells whether the quad is invalid (empty) internal bool IsEmpty { get { return (_A == _B) && (_C == _D); } } internal void GetPoints(List pointBuffer) { pointBuffer.Add(_A); pointBuffer.Add(_B); pointBuffer.Add(_C); pointBuffer.Add(_D); } /// Returns the bounds of the quad internal Rect Bounds { get { return IsEmpty ? Rect.Empty : Rect.Union(new Rect(_A, _B), new Rect(_C, _D)); } } #endregion #region Fields private Point _A; private Point _B; private Point _C; private Point _D; #endregion } } ```