disable subpixel antialiasing for TextBlkItem rendering, close #919

        self.repainting = True

        font_size = self.layout.max_font_size(to_px=True)

        img_array = None

        target_map = QPixmap(self.boundingRect().size().toSize())

        target_map.fill(Qt.GlobalColor.transparent)

        painter = QPainter(target_map)

            return self.scale()

    def paint(self, painter: QPainter, option: QStyleOptionGraphicsItem, widget: QWidget) -> None:

        # subpixel antialiasing is enabled for super().paint upon drawing on some non-transparent background https://github.com/dmMaze/BallonsTranslator/issues/919

        # which can be avoided by calling super().paint first, but it results in disappeared background in editting mode

        # so the checking logic lies here

        if self.is_editting():

            self._draw_accessories(painter)

        option.state = QStyle.State_None

        super().paint(painter, option, widget)

        if not self.is_editting():

            painter.setCompositionMode(QPainter.CompositionMode.CompositionMode_DestinationOver)

            self._draw_accessories(painter)

            painter.setCompositionMode(QPainter.CompositionMode.CompositionMode_SourceOver)

    def _draw_accessories(self, painter: QPainter):

        br = self.boundingRect()

        painter.save()

        if self.background_pixmap is not None:

            painter.setRenderHint(QPainter.RenderHint.SmoothPixmapTransform)

            painter.drawPixmap(br.toRect(), self.background_pixmap)

            painter.drawRect(self.unpadRect(br))

        painter.restore()

        option.state = QStyle.State_None

        super().paint(painter, option, widget)

    def startEdit(self, pos: QPointF = None) -> None:

        self.pre_editing = False