open-interest-chart.md

Open interest and funding

OpenInterestChart draws the pair every perpetual futures desk watches: open interest over price in the upper panel, funding in the lower one. Open interest says how much money is in the trade and funding says which side is paying to be there; together with price they separate a rally that is new buying from one that is shorts covering.

OpenInterestChart(
  points: [
    for (final reading in readings)
      OpenInterestPoint(
        time: reading.time,
        openInterest: reading.oi,
        funding: reading.funding,
        price: reading.close,
      ),
  ],
);

The chart fills its constraints. In a box with no height it takes defaultHeight.

Readings

An OpenInterestPoint is a time, the openInterest then, and optionally the funding rate as a fraction — 0.0001 is one basis point — and the price. A non-finite open interest is a gap in the line; a null funding is a time with no reading and gets no bar.

What the pair says

openInterestMoves(points) reads price and interest together at each step and returns one of four cases:

Price	Open interest	OpenInterestMove
Up	Up	newLongs — new money, long
Down	Down	longsClosing — longs closing out
Down	Up	newShorts — new money, short
Up	Down	shortsCovering — shorts buying back

Anything else — a flat step, a missing price, the first reading — is OpenInterestMove.flat. moveLabel(move) is what each is called.

The panels

Open interest is read for its swings, not its level, so the upper panel is scaled to the range the readings actually cover rather than down to zero. The price line over it has its own scale, since it is there to be compared in shape rather than in level.

Funding bars grow off a zero line in the lower panel, the way every exchange draws them: positive funding — longs paying — rises above it, negative funding hangs below. They are scaled to the largest rate either way, which makes one chart's bars incomparable with another's, so pass fundingMax to pin the scale. fundingShare is how much of the height that panel takes.

Layout

layOutOpenInterest(points, size:, ...) is the layout on its own, without a widget. It returns an OpenInterestLayout with the interestRect and fundingRect, the columnX of each reading, the interestPoints, pricePoints and fundingBars — each null where that reading has no value — the two panels' scales, the fundingMax and the zeroY. layout.indexAt(x) finds the nearest reading. progress reveals the readings left to right, for a draw-in animation.

Touch

onTouch is called with a reading and what the pair did there, and with nulls when the touch leaves. A line is drawn down both panels at that reading, and a card shows its open interest, its funding in basis points and the move; tooltipBuilder replaces the card.

Styling

Field	Default
interestColor, interestFillOpacity	A blue line over a faint wash
priceColor, showPrice	A pale price line over the panel
positiveFundingColor, negativeFundingColor	Green below zero, red above
fundingShare, panelGap, barWidth	0.32, 8 and 0.6
showAxis, axisWidth, axisSteps, interestFormatter	The right axis
fundingFormatter	Writes a rate; basis points by default
crosshairColor, zeroLineColor, gridColor	The lines
animationDuration, animationCurve, animateOnMount	The draw-in

semanticLabel is what a screen reader announces for the chart.

See also

• Liquidity map — where that leveraged money gets out
• Cumulative delta — which side is doing the buying