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Overlays

Any chart series can carry analytical overlays. You give the chart a mask and the window lengths; it computes the values, styles them separately from the series, and clips them to whatever range the chart is showing.

Revenue with SMA, EMA and Bollinger Bands

Adding them with the series​

var mask := DVChart.OVL_SMA | DVChart.OVL_EMA | DVChart.OVL_BBANDS
var idx := chart.add_series_with_overlays("Revenue", values, mask, 5, 9, 6, 2.0)
#                                          name      values  mask  sma ema bb  k

Or afterwards​

var idx := chart.add_series("Revenue", values)
chart.set_series_overlays(idx, DVChart.OVL_SMA | DVChart.OVL_EMA)
chart.set_series_sma_window(idx, 5)      # simple moving average, 5 samples
chart.set_series_ema_window(idx, 9)      # exponential, alpha = 2 / (w + 1)
chart.set_series_bbands_params(idx, 6, 2.0)   # window, k standard deviations

Styling​

Overlays are drawn in their own colours so they read against the series:

chart.set_series_sma_style(idx, Color(0.34, 0.71, 0.91), 2.0)
chart.set_series_ema_style(idx, Color(0.0, 0.62, 0.45), 2.0)
chart.set_series_bbands_style(idx,
	Color(0.94, 0.89, 0.26),          # band lines
	Color(0.94, 0.89, 0.26, 0.10),    # fill between them
	1.5)                              # line width

Notes​

  • The mask is a bitwise OR of OVL_SMA, OVL_EMA and OVL_BBANDS; pass 0 to turn every overlay off for that series.
  • Windows are in samples, not pixels.
  • Overlays honour set_index_range(): they are computed on the series and then clipped to the visible window, so panning a long series does not recompute them.
  • Each series has its own overlays — you can put bands on revenue and leave cost bare.