Expanding standard Polygon class - wpf

Question

I am trying to create a program which can union polygons. I want to create a Polygon class, which can do some operations like Initialize, FindOfOrientation and so on. I am using WPF and with an abstract class - Shape. I want to inherit it and use some properties of this class. But I have problem with Property: "System.Windows.Media.Geometry DefiningGeometry" How should I accomplish this?
class SpecialPolygon: Shape
{
#region Constants
private const int STROKE_THIKNESS = 1; // Толщина линии
private const double OPACITY = 0.5; // Прозрачность
#endregion
int _amountOfVertexes; // Количество сторон полигона
List<Point> _listOfVertexes; // Список всех вершин
List<Stroke> _listOfStrokes; // Список ребер
PointCollection Points { get; set; }
protected override System.Windows.Media.Geometry DefiningGeometry
{
WHAT I SHOULD WRITE IN THIS CASE ???
}
/// <summary>
/// Конструктор с параметрами инициализирует полигон с заданным количеством вершин
/// </summary>
/// <param name="amountOfVertexes">Число вершин</param>
/// <param name="listOfVertexes">Список координат</param>
public SpecialPolygon(int amountOfVertexes, List<Point> listOfVertexes)
{
_amountOfVertexes = amountOfVertexes;
_listOfVertexes = listOfVertexes;
_listOfStrokes = new List<Stroke>();
this.Stroke = System.Windows.Media.Brushes.Black;
this.Fill = System.Windows.Media.Brushes.LightBlue;
this.StrokeThickness = STROKE_THIKNESS;
this.Opacity = OPACITY;
this.Points = new PointCollection();
for (int i = 0; i < _amountOfVertexes; i++)
{
Point a;
a = _listOfVertexes[i];
this.Points.Add(a);
}
// Записываем каждую пару точек в отрезок.(Точка начала отрезка и конца)
for (int i = 0; i < _amountOfVertexes - 1; i++)
{
Stroke stroke = new Stroke(_listOfVertexes[i], _listOfVertexes[i + 1]);
this._listOfStrokes.Add(stroke);
}
// Не забываем записать последний отрезок, соединяющий конец ломанной с её началом
// Таким образом получается полигон
Stroke lastStroke = new Stroke(_listOfVertexes[_amountOfVertexes - 1], _listOfVertexes[0]);
this._listOfStrokes.Add(lastStroke);
}

Answer 1

Rather than going over subject matter in detail that has already been written many times before, I'll just give you a summary and a link to a book that has an excellent section that will answer all of your questions and probably a few that you didn't even have. As #Clemens succinctly said, The DefiningGeometry property would simply return the Geometry that makes up your Shape.
The following example of how to create a Geometry object was taken from the excellent WPF Control Development Unleashed book:
private Geometry GetArcGeometry()
{
Point startPoint = PointAtAngle(Math.Min(StartAngle, EndAngle));
Point endPoint = PointAtAngle(Math.Max(StartAngle, EndAngle));
Size arcSize = new Size(Math.Max(0, (RenderSize.Width –
StrokeThickness)/2),
Math.Max(0, (RenderSize.Height - StrokeThickness)/2));
bool isLargeArc = Math.Abs(EndAngle - StartAngle) 180;
StreamGeometry geom = new StreamGeometry();
using (StreamGeometryContext context = geom.Open())
{
context.BeginFigure(startPoint, false, false);
context.ArcTo(endPoint, arcSize, 0, isLargeArc,
SweepDirection.Counterclockwise, true, false);
}
geom.Transform = new TranslateTransform(StrokeThickness/2,
StrokeThickness/2);
return geom;
}
I'd recommend that you read the Sample: Building a Circular Minute Timer section, starting on page 40, but really, you could do a lot worse than read the whole thing. While I'm suggesting reading material for you, it seems that it might be a good idea for you to read through the various pages of the StackOverflow Help Center... it will help you to get the most out of this website.