Mega Code Archive
How to Determine if two segments are intersecting
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Title: How to Determine if two segments are intersecting
function Intersect(const x1, y1, x2, y2, x3, y3, x4, y4: Double): Boolean;
var
UpperX: Double;
UpperY: Double;
LowerX: Double;
LowerY: Double;
Ax: Double;
Bx: Double;
Cx: Double;
Ay: Double;
By: Double;
Cy: Double;
D: Double;
F: Double;
E: Double;
begin
Result := False;
Ax := x2 - x1;
Bx := x3 - x4;
if Ax 0.0 then
begin
LowerX := x2;
UpperX := x1;
end
else
begin
UpperX := x2;
LowerX := x1;
end;
if Bx 0.0 then
begin
if (UpperX ) or (x3 ) then
Exit;
end
else if (Upperx ) or (x4 ) then
Exit;
Ay := y2 - y1;
By := y3 - y4;
if Ay 0.0 then
begin
LowerY := y2;
UpperY := y1;
end
else
begin
UpperY := y2;
LowerY := y1;
end;
if By 0.0 then
begin
if (UpperY ) or (y3 ) then
Exit;
end
else if (UpperY ) or (y4 ) then
Exit;
Cx := x1 - x3;
Cy := y1 - y3;
d := (By * Cx) - (Bx * Cy);
f := (Ay * Bx) - (Ax * By);
if f 0.0 then
begin
if (d 0.0) or (d f) then
Exit;
end
else if (d 0.0) or (d ) then
Exit;
e := (Ax * Cy) - (Ay * Cx);
if f 0.0 then
begin
if (e 0.0) or (e f) then
Exit;
end
else if (e 0.0) or (e ) then
Exit;
Result := True;
(*
Simple method, yet not so accurate for certain situations and a little more
inefficient (roughly 19.5%).
Result := (
((Orientation(x1,y1, x2,y2, x3,y3) * Orientation(x1,y1, x2,y2, x4,y4))
((Orientation(x3,y3, x4,y4, x1,y1) * Orientation(x3,y3, x4,y4, x2,y2))
);
*)
end;
(* End of SegmentIntersect *)
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