Mega Code Archive
Determine if a point exists within a triangle
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Title: Determine if a point exists within a triangle?
function PointInTriangle(const Px, Py, x1, y1, x2, y2, x3, y3: Double): Boolean;
var
Or1: Integer;
Or2: Integer;
Or3: Integer;
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);
if (Or1 = Or2) and (Or2 = Or3) then
Result := True
else if Or1 = 0 then
Result := (Or2 = 0) or (Or3 = 0)
else if Or2 = 0 then
Result := (Or1 = 0) or (Or3 = 0)
else if Or3 = 0 then
Result := (Or2 = 0) or (Or1 = 0)
else
Result := False;
end;
(* End of PointInTriangle *)
function Orientation(const x1, y1, x2, y2, Px, Py: Double): Integer;
var
Orin: Double;
begin
(* Linear determinant of the 3 points *)
Orin := (x2 - x1) * (py - y1) - (px - x1) * (y2 - y1);
if Orin 0.0 then
Result := +1 (* Orientaion is to the right-hand side *)
else if Orin then
Result := -1 (* Orientaion is to the left-hand side *)
else
Result := 0; (* Orientaion is neutral aka collinear *)
end;
(* End of Orientation *)
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