Lazarus Pascal Requires Chilkat v11.7.0+

QR Code Error Correction Levels

See more QR Code Examples

Demonstrates the four QR error-correction levels. L, M, Q and H allow a reader to recover the data when about 7%, 15%, 25% and 30% of the symbol is damaged or covered. More error correction leaves less room for data, so the same text needs a larger symbol at a higher level. The default is M. The example also shows boostErrorCorrection, which raises the level for free when the chosen version has room to spare. Lazarus Pascal

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.JsonArray,
  Chilkat.Formats,
  Chilkat.JsonObject;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  fmt: TFormats;
  json: TJsonObject;
  jsonOut: TJsonObject;
  levels: TJsonArray;
  i: Integer;
  json2: TJsonObject;

begin
  success := False;

  //  This example requires the Chilkat API to have been previously unlocked.
  //  See Global Unlock Sample for sample code.

  fmt := TFormats.Create;
  json := TJsonObject.Create;
  jsonOut := TJsonObject.Create;
  json.UpdateString('payload.text','https://www.chilkatsoft.com/barcode_overview.asp');

  //  Encode the same text at each level.
  levels := TJsonArray.Create;
  levels.Load('["L","M","Q","H"]');

  for i := 0 to 3 do
    begin
      json.UpdateString('encoding.qr.errorCorrection',levels.StringAt(i));
      success := fmt.QrCode('generate',json,jsonOut);
      if (success = False) then
        begin
          WriteLn(fmt.LastErrorText);
          Exit;
        end;
      WriteLn('level ' + levels.StringAt(i) + ': version ' + jsonOut.IntOf('symbols[0].selectedEncoding.version') + ', ' + jsonOut.IntOf('symbols[0].dimensions.modulesWide')
           + ' modules wide');
    end;

  //  The four symbols.  They hold the same text, and the higher the level, the larger the symbol:

  //  

  //  A symbol often has room left over.  boostErrorCorrection uses it: the level is raised
  //  as far as the same version allows, so the symbol is no larger but is more robust.
  json2 := TJsonObject.Create;
  json2.UpdateString('payload.text','https://chilkatsoft.com');
  json2.UpdateString('encoding.qr.errorCorrection','L');
  success := fmt.QrCode('generate',json2,jsonOut);
  if (success = False) then
    begin
      WriteLn(fmt.LastErrorText);
      Exit;
    end;
  WriteLn('level L requested: version ' + jsonOut.IntOf('symbols[0].selectedEncoding.version') + ', level ' + jsonOut.StringOf('symbols[0].selectedEncoding.errorCorrection'));

  json2.UpdateBool('encoding.qr.boostErrorCorrection',True);
  success := fmt.QrCode('generate',json2,jsonOut);
  if (success = False) then
    begin
      WriteLn(fmt.LastErrorText);
      Exit;
    end;
  WriteLn('level L with boost: version ' + jsonOut.IntOf('symbols[0].selectedEncoding.version') + ', level ' + jsonOut.StringOf('symbols[0].selectedEncoding.errorCorrection'));

  //  Level L, and level M reached by the boost.  The two symbols are the same size:

  //  

  //  Sample output:

  //  level L: version 3, 29 modules wide
  //  level M: version 4, 33 modules wide
  //  level Q: version 5, 37 modules wide
  //  level H: version 6, 41 modules wide
  //  level L requested: version 2, level L
  //  level L with boost: version 2, level M


  fmt.Free;
  json.Free;
  jsonOut.Free;
  levels.Free;
  json2.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.