Firemonkey TCameraComponent quality change when reactivated

问题

I'm building a barcode reader application in Delphi 10.1 Berlin with firemonkey for Android. Based on the CameraComponent sample and using the ZXing library, it was possible to read the barcode.

To initialize the camera, I'm using this code:

procedure TfrmMain.btnOpenReaderClick(Sender: TObject);
begin
  CameraComponent.Active := False;
  CameraComponent.FocusMode := FMX.Media.TFocusMode.ContinuousAutoFocus;
  CameraComponent.Quality := TVideoCaptureQuality.MediumQuality;
  CameraComponent.Active := True;
  CameraComponent.SampleBufferToBitmap(imgCamera.Bitmap, True);
end;

To scan the barcode, I'm running this:

procedure TfrmMain.GetImage;
var
  ReadResult: TReadResult;
begin
  CameraComponent.SampleBufferToBitmap(imgCamera.Bitmap, True);

  if (FScanInProgress) then
    Exit;

  { This code will take every 4 frames. }
  inc(FFrameTake);
  if (FFrameTake mod 4 <> 0) then
    Exit;

  ReadResult := nil;

  ITask(TTask.Create(
    procedure
    begin
      try
        FScanInProgress := True;

        ReadResult := FScanManager.Scan(imgCamera.Bitmap);

        TThread.Synchronize(nil,
          procedure
          begin
          try
            if (ReadResult <> nil) then
            begin
              Label1.Text := ReadResult.text;
              CameraComponent.Active := False;
            end;
          except
            on E: Exception do
              ShowMessage(E.Message);
          end;
        end);
      finally
        ReadResult.Free;
        imgCamera.Bitmap.Free;
        FScanInProgress := false;
      end;
    end)).Start;
end;

After reading the barcode, when I set CameraComponent.Active := True; to start reading a new barcode, the CameraComponent quality is automatically set to high quality, even if the property is set as medium quality when starting the component. This causes the preview of the camera to show at low frame rate. Is there a way to set the default capture setting to medium when reactivating the CameraComponent?

回答1:

Yes you have to setup the camera before you activate it. Like:

CameraComponent1.Quality := TVideoCaptureQuality.MediumQuality;
CameraComponent1.Active := true;

btw: I only stop the camera on Android and not with IOS. That's too slow. I'll close the camera with IOS on application stop. The canvas is not updated anymore then.

procedure TdmGetBarcodeStatus.StopCamera();
begin
    CameraIsActivated := false;
{$IFDEF ANDROID}
    CameraComponent1.Active := false;
{$ENDIF}
end;

Also implement the camera optimization technique in the link provided by Dave. Its speeds up the camera frame rate tremendously.

For a little, I think better scan strategy you can run the image scan progress in a continuous Task.

This is how it can be done:

FParseImagesInProgress is a flag which controls the parsing of the images coming from a TRectangle (RectImage.Fill.Bitmap.Bitmap). Before you stop the camera you set FParseImagesInProgress to false.

procedure TFormCamera.StartParseImageTaskService();
var
    ReadResult: TReadResult;
begin

    if FParseImagesInProgress then
        Exit;

    FParseImagesInProgress := true;

    TTask.Run(
        procedure
        var
            hints: TDictionary<TDecodeHintType, TObject>;
            PossibleFormats: TList<TBarcodeFormat>;
            ScanManager: TScanManager;
            scanBitmap: TBitmap;
        begin
            PossibleFormats := TList<TBarcodeFormat>.Create();
            PossibleFormats.Add(TBarcodeFormat.QR_CODE);

            hints := TDictionary<TDecodeHintType, TObject>.Create();
            hints.Add(TDecodeHintType.POSSIBLE_FORMATS, PossibleFormats);

            ScanManager := TScanManager.Create(TBarcodeFormat.CODE_128, hints);
            scanBitmap := TBitmap.Create();

            try

                while (FParseImagesInProgress) do
                begin

                    ReadResult := nil;

                    try

                        TThread.Synchronize(nil,
                            procedure
                            begin
                                scanBitmap.Assign(RectImage.Fill.Bitmap.Bitmap);
                            end);

                        ReadResult := ScanManager.Scan(scanBitmap);

                    except
                        if Assigned(ReadResult) then
                            FreeAndNil(ReadResult);
                    end;

                    if Assigned(ReadResult) then
                    begin
                        TThread.Synchronize(nil,
                            procedure
                            begin
                                // PlaySound(TATSounds.Good);
                                MarkBarcode(ReadResult, TalphaColors.Deepskyblue);

                                if WasNotLastBarcodeInTimeWindow(ReadResult.Text) then
                                    FBarcodeRequestManager.RequestBarcodeStatus(ReadResult.Text, HotMember, 'myDevice', HotUser,
                                        HotPassword);

                                FLastBarcode := ReadResult.Text;

                            end);

                        FreeAndNil(ReadResult);
                    end;

                    Sleep(MS_BETWEEN_SCAN_FRAMES);

                end; // while

            finally

                if Assigned(scanBitmap) then
                    scanBitmap := nil;

                FreeAndNil(ScanManager);

                if Assigned(PossibleFormats) then
                begin
                    PossibleFormats.Clear;
                    PossibleFormats := nil;
                end;

                if Assigned(ReadResult) then
                    FreeAndNil(ReadResult);

            end;

        end); // end TTask

end;

It is really fast.

Anyway, hope it helps!

来源：https://stackoverflow.com/questions/51830038/firemonkey-tcameracomponent-quality-change-when-reactivated