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procedure viereck(Bit: TBitmap; A,B,C,D: TPoint);
var
 x,y,x2,y2: integer;
 Bit2: TBitmap;
 Line, Line2: PRGBTriple;
begin
 Bit2 := TBitmap.Create;
 Bit2.Assign(Bit);
 Bit.Width:= max(C.X,D.X)-min(A.x,B.x);
 Bit.Height:= max(max(C.Y,D.Y), max(A.Y,B.Y));
 Bit.Canvas.FillRect(rect(0,0,Bit.Width,Bit.Height));
 for y:=0 to Bit2.Height-1 do begin
  Line:=Bit2.ScanLine[y];
  for x:=0 to Bit2.Width-1 do begin
   y2:=round((((A.Y*(1-x/Bit2.Width)+(D.Y*x/Bit2.Width)))*(1-y/Bit2.Height)) +
   (((B.Y*(1-x/Bit2.Width)+(C.Y*x/Bit2.Width)))*(y/Bit2.Height)));
   x2:=round((((A.X*(1-y/Bit2.Height)+(B.X*y/Bit2.Height)))*(1-x/Bit2.Width))+(((D.X*(1-y/ Bit2.Height)+(C.X*y/Bit2.Height)))*(x/Bit2.Width)));
   if (y2<0)or(y2>=Bit.Height)or(x2<0)or(x2>=Bit.Width) then break;
    Line2:=Bit.ScanLine[y2];
   inc(line2,x2);
   Line2^:=Line^;
   inc(line);
  end;
 end;
end;