def processAlgorithm(self, parameters, context, feedback):
        crs = self.parameterAsCrs(parameters, self.TARGET_CRS, context)
        extent = self.parameterAsExtent(parameters, self.EXTENT, context, crs)
        value = self.parameterAsDouble(parameters, self.NUMBER, context)
        pixelSize = self.parameterAsDouble(parameters, self.PIXEL_SIZE, context)

        outputFile = self.parameterAsOutputLayer(parameters, self.OUTPUT, context)
        outputFormat = QgsRasterFileWriter.driverForExtension(os.path.splitext(outputFile)[1])

        rows = max([math.ceil(extent.height() / pixelSize) + 1, 1.0])
        cols = max([math.ceil(extent.width() / pixelSize) + 1, 1.0])

        writer = QgsRasterFileWriter(outputFile)
        writer.setOutputProviderKey('gdal')
        writer.setOutputFormat(outputFormat)
        provider = writer.createOneBandRaster(Qgis.Float32, cols, rows, extent, crs)
        provider.setNoDataValue(1, -9999)

        data = [value] * cols
        block = QgsRasterBlock(Qgis.Float32, cols, 1)
        block.setData(struct.pack('{}f'.format(len(data)), *data))

        total = 100.0 / rows if rows else 0
        for i in range(rows):
            if feedback.isCanceled():
                break

            provider.writeBlock(block, 1, 0, i)
            feedback.setProgress(int(i * rows))

        provider.setEditable(False)

        return {self.OUTPUT: outputFile}

    def processAlgorithm(self, parameters, context, feedback):
        inp_rast = self.parameterAsRasterLayer(parameters, self.INPUT, context)

        grib_filename = self.parameterAsString(parameters, self.OUTPUT, context)
        if not grib_filename:
            raise QgsProcessingException(self.tr('You need to specify output filename.'))

        idp = inp_rast.dataProvider()
        map_settings = iface.mapCanvas().mapSettings()
        crs = map_settings.destinationCrs()
        outputFormat = QgsRasterFileWriter.driverForExtension('.tif')

        height = inp_rast.height()
        width = inp_rast.width()
        inp_block = idp.block(1, idp.extent(), width, height)

        rfw = QgsRasterFileWriter(grib_filename + '.tif')
        rfw.setOutputProviderKey('gdal')
        rfw.setOutputFormat(outputFormat)
        rdp = rfw.createMultiBandRaster(
            Qgis.Float32,
            width,
            height,
            idp.extent(),
            crs,
            2
        )

        rdp.setEditable(True)
        x_block = QgsRasterBlock(Qgis.Float32, width, height)
        y_block = QgsRasterBlock(Qgis.Float32, width, height)
        diag = 1. / sqrt(2)

        # resulting raster has no NODATA value set, which
        # is not treated correctly in MDAL 0.2.0. See
        # see https://github.com/lutraconsulting/MDAL/issues/104
        # therefore set some small value to overcome the issue
        dir_map = {
            0: (1e-7, 1),
            1: (diag, diag),
            2: (1, 1e-7),
            3: (diag, -diag),
            4: (1e-7, -1),
            5: (-diag, -diag),
            6: (-1, 1e-7),
            7: (-diag, diag),
            255: (0, 0)
        }
        for row in range(height):
            for col in range(width):
                dir_ind = inp_block.value(row, col)
                try:
                    x_val, y_val = dir_map.get(dir_ind, 255)
                except TypeError:
                    x_val, y_val = (0, 0)
                x_block.setValue(row, col, x_val)
                y_block.setValue(row, col, y_val)

        rdp.writeBlock(x_block, 1)
        rdp.writeBlock(y_block, 2)
        rdp.setNoDataValue(1, inp_block.noDataValue())
        rdp.setNoDataValue(2, inp_block.noDataValue())
        rdp.setEditable(False)

        # rewrite the resulting raster as GRIB using GDAL for setting metadata
        res_tif = gdal.Open(grib_filename + '.tif')
        grib_driver = gdal.GetDriverByName('GRIB')
        grib = grib_driver.CreateCopy(grib_filename, res_tif)
        band_names = ('x-flow', 'y-flow')
        for i in range(2):
            band_nr = i + 1
            band_name = band_names[i]
            grib_band = grib.GetRasterBand(band_nr)
            grib_band.SetMetadataItem('grib_comment', band_name)
            grib_band.SetNoDataValue(255)
            grib_band.SetDescription(band_name)
            res_tif_band_array = res_tif.GetRasterBand(band_nr).ReadAsArray()
            grib_band.WriteArray(res_tif_band_array)
            feedback.setProgress(band_nr * 50)
        grib = None
        return {self.OUTPUT: grib_filename}