Category: Math
Title: Determine if a 2D point exists within a 2D triangle
Date added: 15.03.2006
Hits: 1225


function PntInTriangle(Px, Py, x1, y1, x2, y2, x3, y3: Double): Boolean;
var
  Or1, Or2, Or3: Double;
begin
  Or1    := Orientation(x1, y1, x2, y2, Px, Py);
  Or2    := Orientation(x2, y2, x3, y3, Px, Py);
  Or3    := Orientation(x3, y3, x1, y1, Px, Py);
  Result := (Or1 = Or2) and (Or2 = Or3);
end;


function Orientation(x1, y1, x2, y2, Px, Py: Double): Integer;
var
  Orin: Double;
begin
  Orin := (x2 - x1) * (py - y1) - (px - x1) * (y2 - y1);
  if Orin > 0.0 then Result := +1  
  else if Orin < 0.0 then Result := -1
  else
    Result := 0;              
end;

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