GraphWithPointer — Ventilator Monitor Waveform Widget

A Flutter CustomPainter widget that mimics the real-time scrolling waveform display found on clinical ventilator monitors. It was built as part of a Flutter + Arduino ventilator project, where continuous sensor data (airway pressure, tidal volume, flow) needs to be rendered as a live, looping waveform — just like a bedside ICU monitor.

The widget accepts a List of data points and a current index (pointer), then renders a scrolling trace that wraps around the screen as new data arrives — replicating the classic "sweeping line" behaviour of medical monitors.

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How It Works

The index value acts as the write head. As your data loop increments index, the widget erases a small block ahead of the pointer and redraws the waveform behind it, creating the illusion of a continuously scrolling signal. All data is automatically scaled to fit the display area based on minY and maxY.

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Parameters

Display customisation

Parameter	Type	Default	Description
backgroundColor	Color	Colors.black	Canvas background color
lineColor	Color	Colors.redAccent	Waveform line color
segmentYColor	Color	Colors.white	Y-axis gridline and label color

Data & scaling

Parameter	Type	Default	Description
dataSet	List	required	The data buffer to render (fixed-length list)
index	int	required	Current write position; drives the sweeping pointer
minY	double	1.0	Minimum expected data value (used for Y scaling)
maxY	double	0.0	Maximum expected data value (used for Y scaling)
totalSegmentY	int	5	Number of horizontal gridline divisions on the Y axis

Tip: Adjusting minY and maxY beyond your actual data range effectively zooms the waveform in or out — useful for emphasising subtle signal variations.

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Basic Usage

// In your state, maintain a fixed-length buffer and a rolling index:
List<double> _pawDataSet = List.filled(150, 0.0);
int _index = 0;

// On each sensor tick, write new data and advance the pointer:
_pawDataSet[_index] = newPressureValue;
_index = (_index + 1) % _pawDataSet.length;

// Pass them to the widget:
GraphWithPointer(
  index: _index,
  dataSet: _pawDataSet,
  minY: 0.0,
  maxY: 80.0,
  totalSegmentY: 5,
  backgroundColor: Colors.black,
  lineColor: Colors.orangeAccent,
  segmentYColor: Colors.white,
)

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Preview

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Notes

• The dataSet list should be pre-allocated to a fixed length (e.g. List.filled(150, 0.0)). The widget does not grow or shrink the buffer.
• shouldRepaint is optimised to only trigger a redraw when index changes, keeping performance smooth during rapid sensor updates.
• For historical/trend review (non-scrolling, with a draggable pointer), see the companion GraphDBWithPointer widget.