How to get the Y value where line intersects with the Y axis

Hi Lucas,

@ the Community: see original question Price Indicators on Y-Axis with full codepen and background on the
requirement

The workflow to get the latest Y-value in the viewport as line intersects the viewport edge is as follows, (in pseudocode):

// 1. Get xMax = xAxis.visibleRange.max 
// 2. FindIndex: xMaxIndex = findIndexOf(xMax, dataSeries.getNativeXValues())
// 3. Get yValue = dataSeries.getNativeYValues().get(xMaxIndex);
// 4. Determine yValueOutsideViewport = xMaxIndex < dataSeries.count()

In SciChart.js code the only thing which is tricky is FindIndex. We wrote a helper function to FindIndex fast to do this (which we plan to include on dataSeries soon).

See question Add custom annotation with fixed x1 value and dynamically changed y1 value with the series data in a real time updated chart. This describes how to place an annotation Y1 at specific y datapoint which corresponds to an x-value.

Adapting the code for your situation, you’d do this:

const findIndex = (dataSeries, xValue) => {
    return wasmContext.NumberUtil.FindIndex(dataSeries.getNativeXValues(), 
         xValue, 
         wasmContext.SCRTFindIndexSearchMode.Nearest, 
         isDataSorted);
};

const xIndex = findIndex(xyDataSeries, xAxis.visibleRange.max); 
const yValue = xyDataSeries.getNativeYValues().get(xIndex);
annotation.y1 = yValue;

Putting this all together, the SeriesValueModifier code has been updated. I’ve done this in the original Codepen linked to on the Price Indicators on Y-Axis forum question.

BTW: If you have a feature request for us to add this functionality into core SciChart, let us know your exact and complete requirements.

Best regards
Andrew

Thank you very much, Andrew, for the explanation and examples!
So much helpful, as always