Firemonkey bitmap scaling without Aliasing on Android

per Ivan Revelli
in Android, Articoli, Delphi, Programmazione
on Aprile 11, 2016

With Delphi , to the Seattle version , when you scale a bitmap image to enlarge using the command “Canvas.DrawBitmap(OiginalBitmap, RectF(0, 0, OiginalBitmap.Width, OiginalBitmap.Height), RectF(0, 0, Width, Height), 1, False);” the interpolation cant be disabled.

A way to eliminate the problem is to manually scale the bitmap directly creating an image pixel by pixel . To do this you need to get canvas.scale and create an image with the native resolution of the Android device .

This helped me for example to generate qrcode on the display of my Android devices that were as sharp as possible, i use the DelphiZXingQRCode to generate the qrcode in the original format.

To draw the qrcode generated from the library I have implemented the following procedure:


procedure TForm2.genQrCodeToImage(DestImage: TImage; ContentText: String);

var

  Local_Row: Integer;

  Local_Column: Integer;

  vPixelB: Integer;

  vPixelW: Integer;

  QRCode: TDelphiZXingQRCode;

  QRCodeBitmap: TBitmapData;

  Row: Integer;

  bmp: FMX.Graphics.TBitmap;

  Column: Integer;

  ms: TMemoryStream;

  bmp2: FMX.Graphics.TBitmap;

  DestW: Int64;

  DestH: Int64;

  pixW: Int64;

  pixH: Int64;

  j: Integer;

  currentRow: Int64;

  k: Int64;

  currentCol: Int64;

begin

  { TODO :

    Inserire nell’url http due parametri :

    1) computer name

    2) servizio di remoting }
  ms := nil;

  bmp := nil;

  bmp2 := nil;
  DestW := round(DestImage.Width  * Canvas.Scale);

  DestH := round(DestImage.Height  * Canvas.Scale);
  DestImage.Bitmap.SetSize(DestW, DestH);

  DestImage.scale.X := 1;

  DestImage.scale.Y := 1;

  vPixelB := TAlphaColorRec.Black;

  // determine colour to use

  vPixelW := TAlphaColorRec.White;

  // determine colour to use

  QRCode := TDelphiZXingQRCode.Create;

  try
    QRCode.Data := ContentText;
    QRCode.Encoding := TQRCodeEncoding(0);

    QRCode.QuietZone := 4;

    bmp := FMX.Graphics.TBitmap.Create;
    bmp.SetSize(DestW,DestH);
    pixW := Trunc(DestW / QRCode.Columns);

    pixH := Trunc(DestH / QRCode.Rows);
    if bmp.Map(TMapAccess.maReadWrite, QRCodeBitmap) then

    begin

      // QRCodeBitmap.SetSize(QRCode.Rows, QRCode.Columns);

      for Local_Row := 0 to QRCode.Rows – 1 do

      begin

        currentRow := (pixH * Local_Row);

        j := 0;

        while J < pixH do
         Begin
          if J > 0 then

           currentRow := currentRow + 1;

          J := J + 1;

          for Local_Column := 0 to QRCode.Columns – 1 do

            begin

              currentCol := (PixW * Local_Column);

              k := 0;

              while K < pixW do
               Begin
                if k > 0 then

                 currentCol := currentCol + 1;

                k := k+1;
                if (QRCode.IsBlack[Local_Row, Local_Column]) then

                begin

                  QRCodeBitmap.SetPixel(currentRow, currentCol, vPixelB);

                end

                else

                begin

                  QRCodeBitmap.SetPixel(currentRow, CurrentCol, vPixelW);

                end;

               End;

            end;

         End;

      end;

      bmp.Unmap(QRCodeBitmap);

    end;

  finally

    QRCode.Free;

  end;

  ms := TMemoryStream.Create;

  bmp.SaveToStream(ms);

  ms.Position := 0;
  DestImage.Bitmap.LoadFromStream(ms);

  try

    if ms <> nil then

      ms.Free;

    if bmp <> nil then

      bmp.Free;

    if bmp2 <> nil then

      bmp2.Free;

  except
  end;

end;