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# C# - Vom Polygonzug zum Rohr

Veröffentlicht von am 12/9/2013
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Aus einer Liste, deren Punkte ein Polygonzug definieren, wird eine neue Liste von Punkten erstellt, die einfach der Methode Graphics.DrawLines(...) übergeben werden muss. Und schwupp wird ein Rohr gezeichnet :)

Aufgerufen werden muss nur die Methode "GetTubePath".
```internal static List<PointF> GetTubePath(List<PointF> Points, int move)
{
List<PointF> output = new List<PointF>();
PointF p11, p12, p21, p22 = PointF.Empty, intercept;
double ang1, ang2;
Direction dir1, dir2;

if (Points.Count == 2)
{
ang1 = AngelCalc(Points[0], Points[1]);
dir1 = Forward(Points[0], Points[1]);
p11 = MovePoint(Points[0], ang1 + (int)dir1, move);
p22 = MovePoint(Points[1], ang1 + (int)dir1, move);

}
else
{
for (int i = 0; i < Points.Count - 2; i++)
{
ang1 = AngelCalc(Points[i], Points[i + 1]);
dir1 = Forward(Points[i], Points[i + 1]);
p11 = MovePoint(Points[i], ang1 + (int)dir1, move);
p12 = MovePoint(Points[i + 1], ang1 + (int)dir1, move);

ang2 = AngelCalc(Points[i + 1], Points[i + 2]);
dir2 = Forward(Points[i + 1], Points[i + 2]);
p21 = MovePoint(Points[i + 1], ang2 + (int)dir2, move);
p22 = MovePoint(Points[i + 2], ang2 + (int)dir2, move);

if (i == 0)
else
{
intercept = GetIntersectPoint(p11, p12, p21, p22);
}
}
}
return output;
}

internal static PointF MovePoint(PointF p, double α, int move)
{
PointF point = new PointF();
point.X = p.X + (float)(Math.Cos(α * Math.PI / 180) * move);
point.Y = p.Y + (float)(Math.Sin(α * Math.PI / 180) * move);
return point;
}

internal enum Direction { Forward = 90, Backward = 270 }

internal static Direction Forward(PointF p1, PointF p2)
{
if (p2.X > p1.X) return Direction.Forward;
else return Direction.Backward;
}

internal static PointF GetIntersectPoint(PointF P1, PointF P2, PointF B1, PointF B2)
{
PointF intersect = new PointF();
float numerator = -P1.Y + B1.Y - ((B1.X - P1.X) * (P2.Y - P1.Y) / (P2.X - P1.X)),

denominator = ((B2.X - B1.X) / (P2.X - P1.X)) * (P2.Y - P1.Y) - (B2.Y - B1.Y);

float fraction = numerator / denominator ;
intersect.X = B1.X + fraction * (B2.X - B1.X);
intersect.Y = B1.Y + fraction * (B2.Y - B1.Y);
return intersect;
}

internal static double AngelCalc(PointF P1, PointF P2)
{
if (P1.X > P2.X) return AngelCalc(P2, P1);

float dy = P2.Y - P1.Y;
float dx = P2.X - P1.X;

if (dx == 0 && dy != 0)
{
if (P1.Y < P2.Y)
return 90f;
else
return 270f;
}
if (dy == 0 && dx != 0)
{
if (P1.X < P2.X)
return 0f;
else
return 180f;
}
double ang2 = Math.Atan((dy) / (dx)) * (180 / Math.PI);

return ang2 ;
}
```
Abgelegt unter Polygon, zeichnen, Winkel, Linie, Schnittpunkt, Rohr.

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