Changeset 49 for trunk/UGeometric.pas

Timestamp:

Nov 26, 2017, 12:32:16 AM (6 years ago)

Author:

chronos

Message:

• Modified: Use generic object list instead of TObjectList.
• Fixed: Avoid division by zero in line intersection calculation.

File:

• trunk/UGeometric.pas (modified) (3 diffs)

trunk/UGeometric.pas

@@ -19 +19 @@
 function RotatePoint(Center, P: TPoint; Angle: Double): TPoint;
 function RotatePoints(Center: TPoint; P: TPointArray; Angle: Double): TPointArray;
-function LineIntersect(LineAP1, LineAP2, LineBP1, LineBP2: TPoint): TPoint;
+function LineIntersect(LineAP1, LineAP2, LineBP1, LineBP2: TPoint;
+  out Intersection: TPoint): Boolean;
 function ArcTan2Point(Point: TPoint): Float;
 function ArcTanPoint(Point: TPoint): Float;
@@ -100 +101 @@
 end;
 
-function LineIntersect(LineAP1, LineAP2, LineBP1, LineBP2: TPoint): TPoint;
+function LineIntersect(LineAP1, LineAP2, LineBP1, LineBP2: TPoint;
+  out Intersection: TPoint): Boolean;
 Var
   LDetLineA, LDetLineB, LDetDivInv: Double;
   LDiffLA, LDiffLB: TPoint;
+  D: Double;
 begin
+  if (LineAP1 = LineAP2) or (LineBP1 = LineBP2) then begin
+    Result := False;
+    Exit;
+  end;
   LDetLineA := LineAP1.X * LineAP2.Y - LineAP1.Y * LineAP2.X;
   LDetLineB := LineBP1.X * LineBP2.Y - LineBP1.Y * LineBP2.X;
@@ -111 +118 @@
   LDiffLB := SubPoint(LineBP1, LineBP2);
 
-  LDetDivInv := 1 / ((LDiffLA.X * LDiffLB.Y) - (LDiffLA.Y * LDiffLB.X));
+  D := ((LDiffLA.X * LDiffLB.Y) - (LDiffLA.Y * LDiffLB.X));
+  if D = 0 then begin
+    // Parallel lines without intersection
+    Result := False;
+    Exit;
+  end;
+  LDetDivInv := 1 / D;
 
-  Result.X := Trunc(((LDetLineA * LDiffLB.X) - (LDiffLA.X * LDetLineB)) * LDetDivInv);
-  Result.Y := Trunc(((LDetLineA * LDiffLB.Y) - (LDiffLA.Y * LDetLineB)) * LDetDivInv);
+  Intersection.X := Trunc(((LDetLineA * LDiffLB.X) - (LDiffLA.X * LDetLineB)) * LDetDivInv);
+  Intersection.Y := Trunc(((LDetLineA * LDiffLB.Y) - (LDiffLA.Y * LDetLineB)) * LDetDivInv);
+  Result := True;
 end;