Ninjascipt and Alerts evaluation

Desktop SDK - Add Ons
1

I’m looking for a way to evaluate an Alert, one condition at a time, for a given time and instrument value (not the current bar value, but a range of values)

Under NinjaTrader.NinjaScript.DrawingTools.Polygon I’m seeing the function:

IsAlertConditionTrue(AlertConditionItem conditionitem, Condition condition, ChartAlertValue[] values, ChartControl chartControl, ChartScale chartScale)

Are there any examples on how to use this function? Is this the right function for what I’m trying to do?

Any help would be appreciated, thanks

2

No, I would not use Polygon.IsAlertConditionTrue() as a general-purpose evaluator for an arbitrary time/price range.

That method is part of the drawing-tool alert contract. The built-in Polygon implementation only exposes CrossInside and CrossOutside. It converts each ChartAlertValue from time/value coordinates into chart pixels, checks whether that point is inside the polygon, and then uses the supplied values to detect a crossing. So the array is there for the alert engine’s transition test, not as a general historical range-query API.

For your case I would separate the two jobs:

  1. Build an ordered set of samples for the instrument and time range you want to evaluate.
  2. Run a pure predicate against each sample, for example IsInsidePolygon(time, price).
  3. Compare consecutive results if you need a cross rather than a simple inside/outside result.
  4. Trigger Alert() only when the state changes in the direction you care about.

If you are building your own DrawingTool, then overriding GetValidAlertConditions() and IsAlertConditionTrue() is the right integration point. If this is an indicator, strategy or AddOn, calling Polygon’s override directly is the wrong layer because it depends on ChartControl, ChartScale, panel coordinates and the alert engine’s expected value history.

If you share whether the range is a set of historical bars, tick data, or chart mouse coordinates, the clean implementation differs slightly.

3

I would be evaluating chart mouse coordinates for IsInsidePolygon()

4

If the inputs are chart mouse coordinates, stay in chart-pixel space for the hit test.

Convert the mouse point and every polygon anchor into the same panel coordinates. Then run the point-in-polygon test on those X/Y values. Do not convert the mouse price back into a historical series first.

The important checks are:

  • use the polygon’s own ChartPanel and ChartScale;
  • account for the panel’s X/Y offsets;
  • reject the test while anchors or scale are unavailable;
  • decide explicitly whether a point on an edge counts as inside;
  • recompute after zoom, scroll or scale changes.

I would keep this as a small pure function such as IsInsidePolygon(Point mouse, IReadOnlyList vertices) and keep ChartControl/ChartScale conversion outside it. That makes edge, vertex, inside and outside cases easy to test.

Four useful cases are: center point inside, point outside, point exactly on an edge, and the same data point after a chart zoom. The last case proves the coordinate conversion is refreshed instead of using stale pixels.