Žarko Gajić: FireMonkey / Mobile (Android, iOS) QR Code Generation Using Delphi XE 5 / DelphiZXingQRCode

The DelphiZXingQRCode unit, ported from ZXing by Debenu, allows to easily add QR Code generation to your Delphi VCL applications.

While the DelphiZXingQRCode was designed to support VCL applications (and be used in newer as well as in older Delphi versions), it can also easily be “upgraded” for Fire Monkey applications – be it desktop or mobile (Android, iOS).

DelphiZXingQRCode -> FireMonkey Support

To FireMonkey-enable the DelphiZXingQRCode unit a few changes to the source code were required.

The unit uses “contnrs” (System.Contnrs.pas) unit which implements TObjectList (used by the unit) and other container like classes. Under FireMonkey for mobile, more specifically under ARC, the classes contained in System.Contnrs.pas cannot be used because they are not ARC compliant.

Equivalent classes are to be found in System.Generics.Collections.pas (ARC compliant) where generics versions of TObjectList is defined.

Therefore, the first change is to replace “uses contnrs, …” with “uses System.Generics.Collections, …”

This also requires to make changes like: from “Blocks: TObjectList;” to “Blocks: TObjectList<TBlockPair>;” – that is to use strongly typed generics list classes.

Further, there are lots of “ansistring” and “widestring” types used for parameters in various functions inside the unit. If you want to go mobile, those are not supported and you should use “string”. More info here: Migrating Delphi Code to Mobile from Desktop.

Therefore, the second change to the unit would be to replace “widestring” with “string” and “ansistring” with “array of byte” (or something else as explained in the article).

Single Pixel Drawing (and Other Canvas Drawing) FireMonkey Style

In the VCL, the TCanvas class allows accessing single pixels through the “Canvas.Pixels()” property. In FireMonkey this is not supported and you have to use the SetPixel property of a TBitmapData instance.

Once the qr code is generated, to convert it to a bitmap image, in FireMonkey:

var
  QRCode: TDelphiZXingQRCode;
  Row, Column: Integer;
  pixelColor : TAlphaColor;
  vBitMapData : TBitmapData;
  rSrc, rDest : TRectF;
  s : widestring;
begin
  QRCode := TDelphiZXingQRCode.Create;
  try
    QRCode.Data := edtText.Text;
    QRCode.Encoding := TQRCodeEncoding(cmbEncoding.ItemIndex);
    QRCode.QuietZone := StrToIntDef(edtQuietZone.Text, 4);
    QRCodeBitmap.SetSize(QRCode.Rows, QRCode.Columns);
    for Row := 0 to QRCode.Rows - 1 do
    begin
      for Column := 0 to QRCode.Columns - 1 do
      begin
        if (QRCode.IsBlack[Row, Column]) then
          pixelColor := TAlphaColors.Black
        else
          pixelColor := TAlphaColors.White;

        if QRCodeBitmap.Map(TMapAccess.maWrite, vBitMapData)  then
        try
          vBitMapData.SetPixel(Column, Row, pixelColor);
        finally
          QRCodeBitmap.Unmap(vBitMapData);
        end;
      end;
    end;
  finally
    QRCode.Free;
  end;

  //refresh image control imgQRCode is a TImage
  {code below}
end;

Note: compare this with the VCL approach of TDelphiZXingQRCode usage.

VCL’s Canvas.StretchDraw to FMX’s Canvas.DrawBitmap

There’s no StrecthDraw in FMX’s Canvas class. There’s DrawBitmap. StretchDraw by default does no antialiasing. FMX does. So I had to play a little until I was able to make it work correctly.

I’ve decided to use TImage and not TPaintBox as I was simply not able to make TPictureBox in FireMonkey draw what I wanted

Using TImage, the code to get/display the generated QR Code is as follows:

  //refresh image. imgQRCode is a TImage

  imgQRCode.Bitmap.SetSize(QRCodeBitmap.Width, QRCodeBitmap.Height);

  rSrc := TRectF.Create(0, 0, QRCodeBitmap.Width, QRCodeBitmap.Height);
  rDest := TRectF.Create(0, 0, imgQRCode.Bitmap.Width, imgQRCode.Bitmap.Height);

  if imgQRCode.Bitmap.Canvas.BeginScene then
  try
    imgQRCode.Bitmap.Canvas.Clear(TAlphaColors.White);

    imgQRCode.Bitmap.Canvas.DrawBitmap(QRCodeBitmap, rSrc, rDest, 1);
  finally
    imgQRCode.Bitmap.Canvas.EndScene;
  end;

Aliasing – Do Not Need It!

By default, in FMX, when using DrawBitmap to resize it, antialiasing is used by default. There are two properties you need to set to ensure a bigger copy of your (small) qr code is drawn pixel-copy-perfect.

begin
  imgQRCode.DisableInterpolation := true;
  imgQRCode.WrapMode := TImageWrapMode.iwStretch;
end;

In a FireMonkey Desktop application, this works as expected.

On FireMonkey Mobile it does not – the resized image is still blurred (antialiasing used).

That’s it. QR Codes generation in FireMonkey – both desktop and mobile!

Download the FMX version of DelphiZXIngQRCode.pas: FMX-DelphiZXIngQRCode

Comments are welcome (even more if you know how to resize a bitmap in FireMonkey on mobile without antialiasing)!