QR Codes encoded by DelphiZXingQRCode not decodable with ErrorCorrectionLevel > Low

Question

I am using this Delphi-Unit. I am forced to use this old Delphi implementation, so don't ask about that: https://github.com/foxitsoftware/DelphiZXingQRCode

The QRcodes it produces are decoded by any decoders just fine, as long as I keep the error correction level at "Low". If I increase the error correction level, the generated codes can not be decoded by any decoder I tried so far. But I am forced (by a standard) to use an error correction level of Medium, no more no less.

However it is not clear how to increase the error correction level (ecl from now on). I assume it to be hardcoded in the file DelphiZXingQRCode on line 3491: Level.FBits := 1. I found some information on hexnumbers representing ecls, but I can't find it now. But I tried those hexnumbers as bits and the ecl-bits on the QRcode changed accordingly. So I assumed the hexnumbers to be correct (1=Low, 0=Medium, 2=High, 3=Quartile).

Here is an example of a QRcode with Level.FBits := 2, meaning I wanted the ecl to be "High". The content ist "Hello world". The cross image in the middle is part of a standard [sic] I have to implement, so don't ask about that.

Has anyone any idea how to fix this? I tried...well...I tried to understand the code but it's too much. I just can't fix it. If I can't get it fixed by someone else, I will have to...find another solution. Which will be a problem.

Answer 1

Solved. See code below. Method GenerateQRCode() now requires a parameter for the ErrorCorrectionLevel: Integers 0-3. Seems to work. I had to remove some unchanged lines, because the file is too large for StackOverflow. Merge yourself.

    unit DelphiZXingQRCode;

    // ZXing QRCode port to Delphi, by Debenu Pty Ltd
    // www.debenu.com

    // Original copyright notice
    (*
     * Copyright 2008 ZXing authors
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     *      http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     *)

    interface

    type
      TQRCodeEncoding = (qrAuto, qrNumeric, qrAlphanumeric, qrISO88591, qrUTF8NoBOM, qrUTF8BOM);
      T2DBooleanArray = array of array of Boolean;

      TDelphiZXingQRCode = class
      protected
        FData: WideString;
        FRows: Integer;
        FColumns: Integer;
        FEncoding: TQRCodeEncoding;
        FQuietZone: Integer;
        FElements: T2DBooleanArray;
        FErrorCorrectionLevel: integer;
        procedure SetEncoding(NewEncoding: TQRCodeEncoding);
        procedure SetData(const NewData: WideString);
        procedure SetQuietZone(NewQuietZone: Integer);
        procedure SetErrorCorrectionLevel(value: integer);
        function GetIsBlack(Row, Column: Integer): Boolean;
        procedure Update;
      public
        constructor Create;
        property Data: WideString read FData write SetData;
        property Encoding: TQRCodeEncoding read FEncoding write SetEncoding;
        property ErrorCorrectionLevel: integer read fErrorCorrectionLevel write SetErrorCorrectionLevel;
        property QuietZone: Integer read FQuietZone write SetQuietZone;
        property Rows: Integer read FRows;
        property Columns: Integer read FColumns;
        property IsBlack[Row, Column: Integer]: Boolean read GetIsBlack;
      end;

    implementation

    uses
      SysUtils,
      contnrs, Math, Classes;

    type
      TByteArray = array of Byte;
      T2DByteArray = array of array of Byte;
      TIntegerArray = array of Integer;

    // File too large for Stackoverflow: Deleted unchanged lines.

    { TErrorCorrectionLevel }

    procedure TErrorCorrectionLevel.Assign(Source: TErrorCorrectionLevel);
    begin
      Self.fOrdinal := Source.FOrdinal;
    end;

    constructor TErrorCorrectionLevel.Create(ordinalValue: integer);
    begin

      fOrdinal:=0;
      if (ordinalValue >= 0) and (ordinalValue <=3) then
        fOrdinal:=ordinalValue;
    end;

    function TErrorCorrectionLevel.GetBits: integer;
    begin
      if fOrdinal = 0 then  // level L
        result:=1
      else
      if fOrdinal = 1 then  // level M
        result:=0
      else
      if fOrdinal = 2 then  // level Q
        result:=3
      else
      if fOrdinal = 3 then  // level H
        result:=2
      else
        result:=1;
    end;


    // File too large for Stackoverflow: Deleted unchanged lines.

    procedure TDelphiZXingQRCode.SetErrorCorrectionLevel(value: integer);
    begin
      if (value < 0) or (value > 3) then
        raise Exception.Create('invalid error correction value. must be in range 0..3.');

      if value <> fErrorCorrectionLevel then
      begin
        FErrorCorrectionLevel:=value;
        Update;
      end;
    end;

    procedure TDelphiZXingQRCode.SetQuietZone(NewQuietZone: Integer);
    begin
      if ((FQuietZone <> NewQuietZone) and (NewQuietZone >= 0) and (NewQuietZone <= 100)) then
      begin
        FQuietZone := NewQuietZone;
        Update;
      end;
    end;

    procedure TDelphiZXingQRCode.Update;
    begin
      FElements := GenerateQRCode(FData, Ord(FEncoding), FErrorCorrectionLevel);
      FRows := Length(FElements) + FQuietZone * 2;
      FColumns := FRows;
    end;
    end.