LineIntersection + InnerBox

{$I SimbaExt/SimbaExt.simba}

{$DEFINE NICEDEBUG}
type TLine = record A,B:TPoint; end;
var bmp:Integer;


function FindIntersection(L1,L2:TLine): TPoint;
var
  D,dx,dy:Extended;
  ax1,ax2,bx1,bx2,ay1,ay2,by1,by2:Int32;
begin
  ax1 := L1.a.x;  ax2 := L1.b.x;
  bx1 := L2.a.x;  bx2 := L2.b.x;
  ay1 := L1.a.y;  ay2 := L1.b.y;
  by1 := L2.a.y;  by2 := L2.b.y;

  D := (ax1-ax2)*(by1-by2) - (ay1-ay2)*(bx1-bx2);
  if D <> 0 then
  begin
    dx := ((bx1-bx2)*(ax1*ay2-ay1*ax2)-(ax1-ax2)*(bx1*by2-by1*bx2))/d;
    dy := ((by1-by2)*(ax1*ay2-ay1*ax2)-(ay1-ay2)*(bx1*by2-by1*bx2))/d;
    Result.x := Round(Dx);
    Result.y := Round(Dy);
  end else
    RaiseException('No Intersection');
end;


function InnerBox(Rect:TPointArray): TBox;
var
  B:TBox; {$IFDEF NICEDEBUG} l:TPointArray; {$ENDIF}
  upper,lower:TPoint;
begin
  B := Rect.Bounds();
  {$IFDEF NICEDEBUG}
  se.TPALine(l,B.ToCoords()[2],B.ToCoords()[0]);
  se.TPALine(l,B.ToCoords()[3],B.ToCoords()[1]);
  DrawTPABitmap(bmp, l, $008800);
  DrawTPABitmap(bmp, EdgeFromBox(B), $555555);
  {$ENDIF}

  if (Rect[1].distanceTo(Rect[2]) > Rect[2].distanceTo(Rect[3])) then
  begin
    upper := FindIntersection([Rect[1],Rect[2]], [B.ToCoords()[0],Rect.Mean()]);
    lower := FindIntersection([Rect[3],Rect[0]], [B.ToCoords()[2],Rect.Mean()]);
    Result := [Upper.x+1,Upper.y+1,Lower.x-1,Lower.y-1];
  end else begin
    upper := FindIntersection([Rect[0],Rect[1]], [B.ToCoords()[1],Rect.Mean()]);
    lower := FindIntersection([Rect[2],Rect[3]], [B.ToCoords()[3],Rect.Mean()]);
    Result := [Lower.x+1,Upper.y+1,Upper.x-1,Lower.y-1];
  end;

  {$IFDEF NICEDEBUG}
  DrawTPABitmap(bmp, se.TPACross(upper,4), $FFFF00);
  DrawTPABitmap(bmp, se.TPACross(lower,4), $00FFFF);
  {$ENDIF}
end;



var i: Integer;
    tpa: TPointArray;
    B:TBox;
begin
  bmp := CreateBitmap(600, 600);
  TPA := FindTPAEdges(TPAFromBox([50,50, Random(100,220),Random(100,220)]));
  TPA := TPA.Rotate(Random(360));

  B := InnerBox(TPA.BoundingBox());

  DrawTPABitmap(bmp, tpa, 255);
  DrawTPABitmap(bmp, EdgeFromBox(B), $FFFFFF);
  DisplayDebugImgWindow(300, 300);
  DrawBitmapDebugImg(bmp);
  FreeBitmap(bmp);
end;