Mega Code Archive
How to Determine if a 2D point exists within a 2D triangle
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Title: How to Determine if a 2D point exists within a 2D triangle
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;
(* End Of PntInTriangle *)
function Orientation(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 0.0 then Result := -1 (* Orientaion is to the left-hand side *)
else
Result := 0; (* Orientaion is neutral if result is 0 *)
end;
(* End Of Orientation *)
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