class operator TRectF.Add

[Gustav Schubert 25]

Ha, here at home, today, I needed to do this test:
 

procedure Test;
var
  R1, R2, R3: TRectF;
begin
{
 TRectF from System.Types,
   when calling class operator TRectF.Add in 10.1 Berlin,
     will call class function TRectF.Union,
       which will call UnionRectF(Result, R1, R2),
         which will return Zero if result is Empty. <-- wrong ?

  The c++ code given in the docwiki does not do this. (please check)
 
  https://docwiki.embarcadero.com/Libraries/Alexandria/en/System.Types.TRectF
}

  R1 := TRectF.Create(-1, 0, 1, 0);
  R2 := TRectF.Create(0, -1, 0, 1);
  R3 := R1 + R2; // (0, 0, 0, 0) unexpected

  R1 := TRectF.Create(-1, 0, 1, 0.1);
  R2 := TRectF.Create(0, -1, 0.1, 1);
  R3 := R1 + R2; // (-1, -1, 1, 1) // as expected
end;

 

[mvanrijnen 121]

System.Types, causes this, strange, TRectF not designed to handle negative numbers?:

 

function TRectF.IsEmpty: Boolean;
begin
  Result := (Right <= Left) or (Bottom <= Top);
end;

 

so the next one returns just an empty rect:

function UnionRectF(out Rect: TRectF; const R1, R2: TRectF): Boolean;
var
  tmpRect: TRectF;
begin
  tmpRect := R1;
  if not R2.IsEmpty then
  begin
    if R2.Left < R1.Left then tmpRect.Left := R2.Left;
    if R2.Top < R1.Top then tmpRect.Top := R2.Top;
    if R2.Right > R1.Right then tmpRect.Right := R2.Right;
    if R2.Bottom > R1.Bottom then tmpRect.Bottom := R2.Bottom;
  end;
  Result := not tmpRect.IsEmpty;
  if not Result then
  begin
    tmpRect.Top :=0.0;
    tmpRect.Bottom := 0.0;
    tmpRect.Left := 0.0;
    tmpRect.Right := 0.0;
  end;
  Rect := tmpRect;
end;

 

Edited July 28, 2022 by mvanrijnen

[Uwe Raabe 1879]

5 minutes ago, mvanrijnen said:

TRectF not designed to handle negative numbers?:

That is not the case here. Negative numbers are allowed. In both cases the non-zero borders are ordered correctly.

 

The check for IsEmpty on both rectangles is a logical flaw. A Union of two empty rectangles can result in a non-empty rectangle.

 

@Gustav Schubert

Please file a bug report in QP.

[Gustav Schubert 25]

Thanks for the two good comments above (code context and wording). QP tells me that I do not have permission to create a report, but here are the steps I prepared, please feel free to use them.
 

function Test: Boolean;
var
  P1, P2: TPointF;
  P3, P4: TPointF;
  R1, R2: TRectF;
  ActualResult: TRectF;
  ExpectedResult: TRectF;
begin
  P1 := TPointF.Create(-1, 0);
  P2 := TPointF.Create(1, 0);

  P3 := TPointF.Create(0, -1);
  P4 := TPointF.Create(0, 1);

  { imagine rectangles that hold the two points of a line }
  R1 := TRectF.Create(P1, P2); // horizontal line
  R2 := TRectF.Create(P3, P4); // vertical line

  ActualResult := R1 + R2;
  ExpectedResult := TRectF.Create(-1, -1, 1, 1);

  result := ActualResult = ExpectedResult;
end;

Title: TRect.Add and UnionF problem with Empty rectangles

Description: Class operator Add of TRectF has a problem with Emtpy operands. It will return Zero when it should not. It is understood that the actual problem is the implementation of UnionRectF.
 

[Uwe Raabe 1879]

https://quality.embarcadero.com/browse/RSP-38757