This code snippet demonstrates how to create a Zigzag indicator based on the Donchian channel values in ProBuilder. The Zigzag indicator is used to filter out market noise and identify significant trends and changes in market prices.

defparam drawonlastbaronly=true
// --- period = 40 // --------------
du = DonchianChannelUp[period]
dd = DonchianChannelDown[period]
mid = DonchianChannelCenter[period]

if high > du then
    ihigh = high
    ihighbar = barindex
endif

if low < dd then
    ilow = low
    ilowbar = barindex
endif

if close crosses over mid then
    $zz[zz] = ilow
    $zzbar[zz] = ilowbar
    $zzdir[zz] = -1
    zz=zz+1
endif

if close crosses under mid then
    $zz[zz] = ihigh
    $zzbar[zz] = ihighbar
    $zzdir[zz] = 1
    zz=zz+1
endif

if islastbarupdate then
    for i = zz-1 downto 0 do
        drawsegment($zzbar[i],$zz[i],$zzbar[i+1],$zz[i+1])
    next
endif

return //du,dd

The code snippet above is structured to calculate and plot a Zigzag indicator using the upper, lower, and center bands of the Donchian channel. Here's a step-by-step explanation:

• Initialization: The drawonlastbaronly parameter is set to true, ensuring that drawing commands are executed only on the last bar update to optimize performance.
• Donchian Channel Calculation: The variables du, dd, and mid are assigned the upper, lower, and center values of the Donchian channel, respectively, for the specified period.
• High and Low Detection: The script checks if the current high is greater than the upper Donchian band (du) or if the current low is less than the lower Donchian band (dd). If true, it records the bar index and the high/low values.
• Zigzag Calculation: The Zigzag points are determined based on the crossing of the close price over or under the mid Donchian band. If the close crosses over, a downward Zigzag point is recorded; if it crosses under, an upward Zigzag point is noted.
• Plotting: If it's the last bar update, the script draws segments between recorded Zigzag points using the drawsegment function, visually representing the Zigzag on the chart.

This implementation helps in visualizing significant price movements, filtering out smaller price changes, and potentially identifying trend reversals.