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Cumulative delta

Running delta over a session with per-bar buying and selling beneath

CumulativeDeltaChart draws buying less selling as a running total, with each bar's own delta in a panel beneath it, and marks the bars where price and delta disagreed.

CumulativeDeltaChart(
  bars: deltaBarsFromFootprint(footprintBars),
);

It is the companion to the footprint chart: deltaBarsFromFootprint(bars) takes each footprint bar's delta and close, so the same data drives both.

The chart fills its constraints. When the height is unbounded, it uses defaultHeight.

Data

DeltaBar field Description
time When the bar began
delta Buying less selling in that bar
price The close, used to read divergences; null leaves them out
data Arbitrary app data, returned on touch

cumulativeDelta(bars) returns the running total. A delta that is not finite is skipped rather than poisoning everything after it.

Divergences

deltaDivergences(bars, lookback: 10) returns the bars where price made an extreme the cumulative delta did not follow:

  • bearish — price is the highest of the window, the running total is not: the move up was not bought.
  • bullish — price is the lowest of the window, the running total is not: the move down was not sold.

Bars without a price are skipped, as are the first lookback bars, which have no window behind them. The chart marks each one with a small triangle pointing the way it warns; showDivergences: false turns them off, and divergenceLookback sets the window.

Layout

Parameter Description
histogramFraction How much of the height the per-bar panel takes (default 0.3)
panelGap The gap between the two panels
barSpacing Pixels taken off each side of a delta column
min, max Ends of the running total's axis; null reads them off the bars, always including zero
axisWidth, timeAxisHeight, showValueAxis, showTimeAxis The axes
padding Space around the chart

layOutCumulativeDelta(bars, bounds, …) returns the CumulativeDeltaLayout the chart paints — the two panel rects, the line points, the per-bar column rects, the totals and largestDelta — and layout.indexAt(dx) finds the bar nearest a position.

Appearance

Parameter Description
lineColor, lineWidth, fillOpacity The running total and its shading
buyColor, sellColor Columns above and below zero
bearishDivergenceColor, bullishDivergenceColor The divergence marks
gridColor, crosshairColor Grid and crosshair
valueFormatter, timeFormatter, axisLabelStyle Axis label text
tickCount, backgroundColor Ticks and background

Touch

Pointer events are read raw, so the crosshair follows a drag at once. onTouch reports a CumulativeDeltaTouchDetails with the bar's index, the bar itself, the running total there and where it sits, and null when the pointer leaves.

CumulativeDeltaChart(
  bars: bars,
  tooltipBuilder: (context, details) => Card(
    child: Padding(
      padding: const EdgeInsets.all(8),
      child: Text('delta ${details.bar.delta}\n'
          'total ${details.total}'),
    ),
  ),
);

Animation

animationDuration draws the line in from the left; animationCurve eases it and animateOnMount controls whether the first build animates. The chart animates again whenever bars changes identity.