ScalableText

scalable_text.dart

class ScalableText extends StatefulWidget {
  const ScalableText(
    this.text, {
    required this.fontSize,
    this.onTextScaled,
    Key? key,
  }) : super(key: key);

  final TextSpan text;
  final double fontSize;
  final ValueSetter<double>? onTextScaled;

  @override
  State<ScalableText> createState() => _ScalableTextState();
}

class _ScalableTextState extends State<ScalableText> {
  double _fontSize = 30.0;
  double _baseFontSize = 30.0;
  double _fontScale = 1;
  double _baseFontScale = 1;

  @override
  void initState() {
    _baseFontSize = widget.fontSize;
    _fontSize = _baseFontSize;
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onScaleStart: (ScaleStartDetails details) {
        _baseFontScale = _fontScale;
      },
      onScaleUpdate: (ScaleUpdateDetails scaleUpdateDetails) {
        // don't update the UI if the scale didn't change
        if (scaleUpdateDetails.scale == 1.0) {
          return;
        }
        _fontScale =
            (_baseFontScale * scaleUpdateDetails.scale).clamp(0.5, 5.0);
        setState(() {
          _fontSize = _fontScale * _baseFontSize;
        });
      },
      onScaleEnd: (ScaleEndDetails details) {
        // don't update the UI if the font size didn't change
        if (_fontScale == _baseFontScale) {
          return;
        }
        widget.onTextScaled?.call(_fontSize);
      },
      child: MongolText.rich(
        widget.text,
        style: TextStyle(fontSize: _fontSize),
      ),
    );
  }
}