How to draw a line between two pivots

A pivot high is a bar whose high is above the highs of the bars around it. You know it only after the next bar closes, so test one bar back, on a closed bar: high[1] > high[2] and high[1] > high is true on the bar after the pivot. On a forming bar high still moves, so the test can pass and later fail; barstate.isconfirmed waits for the close. Keep the last pivot’s bar and price in static variables, and when the next pivot comes draw a line from the old one to it. line.new is a drawing, so it may sit inside an if.

//@lipi=2
indicator("Line between swing highs", overlay=true)
static int lastIndex = -1
static float lastHigh = 0.0
isPivot = high[1] > high[2] and high[1] > high
if barstate.isconfirmed and isPivot {
    if lastIndex >= 0 {
        line.new(lastIndex, lastHigh, bar_index - 1, high[1], color=color.red)
    }
    lastIndex := bar_index - 1
    lastHigh := high[1]
}

The pivot is on bar bar_index - 1, so that is the x of the line’s end. A bar index is what line.new takes by default.
On the first bars high[2] is na, the comparison is na, and an if on na does not run.
A pivot low is the mirror: low[1] < low[2] and low[1] < low.
Each line is a drawing, and a script keeps 50 of each kind unless max_lines_count says more (see Lines, labels, boxes and polylines and Limits).

For a wider test, with several bars on each side, talib.highest and talib.lowest give the extremes of a window. See Referencing previous bars for what high[1] reads.

Manual

Use Lipi with AI

Reference

How to draw a line between two pivots