Indicator Buffers & Drawing Styles

Master indicator buffers, drawing modes (line, histogram, arrow, candles), and color customization.

Understanding Buffers and Plots

In MQL5, indicator buffers and plots are separate concepts:

  • Buffers are arrays that store calculated values. Some are drawn on the chart, others are used internally for calculations.
  • Plots are the visual representations. Each plot uses one or more buffers depending on the drawing style.

The number of buffers is always >= the number of plots. For example, a candlestick plot requires 4 buffers (open, high, low, close) but is only 1 plot.

Drawing Styles Reference

MQL5 offers 18 drawing styles. Here are the most commonly used:

DRAW_LINE — A continuous line connecting values. Uses 1 buffer. The most common style for moving averages, channels, and signal lines.

#property indicator_type1 DRAW_LINE
#property indicator_color1 clrDodgerBlue
#property indicator_width1 2
#property indicator_style1 STYLE_SOLID  // SOLID, DASH, DOT, DASHDOT

DRAW_HISTOGRAM — Vertical bars from zero line. Uses 1 buffer. Perfect for oscillator values, volume displays, and momentum bars.

#property indicator_type1 DRAW_HISTOGRAM
#property indicator_color1 clrGreen
#property indicator_width1 3

DRAW_HISTOGRAM2 — Vertical bars between two values. Uses 2 buffers. Great for showing ranges and fill areas.

DRAW_ARROW — Draws symbols at specific points. Uses 1 buffer. Ideal for buy/sell signals, entry/exit markers.

#property indicator_type1 DRAW_ARROW
#property indicator_color1 clrLime
// Set the arrow code in OnInit:
PlotIndexSetInteger(0, PLOT_ARROW, 233);  // up arrow
// Common codes: 233=up arrow, 234=down arrow, 159=dot, 108=star

DRAW_COLOR_LINE — A line that changes color based on conditions. Uses 2 buffers (data + color index). Powerful for showing trend direction with color.

#property indicator_buffers 2
#property indicator_plots   1
#property indicator_type1   DRAW_COLOR_LINE
#property indicator_color1  clrLime,clrRed,clrGray  // up to 64 colors
#property indicator_width1  2

Multi-Color Line Example

A moving average that is green when price is above it and red when below:

#property indicator_chart_window
#property indicator_buffers 2
#property indicator_plots   1
#property indicator_type1   DRAW_COLOR_LINE
#property indicator_color1  clrLime,clrRed
#property indicator_width1  2

input int MAPeriod = 20;

double maBuffer[];
double colorBuffer[];  // 0=green(above), 1=red(below)

int OnInit()
{
    SetIndexBuffer(0, maBuffer, INDICATOR_DATA);
    SetIndexBuffer(1, colorBuffer, INDICATOR_COLOR_INDEX);
    return INIT_SUCCEEDED;
}

int OnCalculate(const int rates_total,
                const int prev_calculated,
                const datetime &time[],
                const double &open[],
                const double &high[],
                const double &low[],
                const double &close[],
                const long &tick_volume[],
                const long &volume[],
                const int &spread[])
{
    int start = (prev_calculated == 0) ? MAPeriod : prev_calculated - 1;

    for(int i = start; i < rates_total; i++)
    {
        // Calculate SMA
        double sum = 0;
        for(int j = 0; j < MAPeriod; j++)
            sum += close[i - j];
        maBuffer[i] = sum / MAPeriod;

        // Set color: 0=green if price above MA, 1=red if below
        colorBuffer[i] = (close[i] >= maBuffer[i]) ? 0 : 1;
    }

    return rates_total;
}

Buy/Sell Signal Arrows

Using DRAW_ARROW to mark entry points:

#property indicator_chart_window
#property indicator_buffers 2
#property indicator_plots   2

#property indicator_type1  DRAW_ARROW
#property indicator_color1 clrLime
#property indicator_width1 2
#property indicator_type2  DRAW_ARROW
#property indicator_color2 clrRed
#property indicator_width2 2

double buySignal[];
double sellSignal[];

int OnInit()
{
    SetIndexBuffer(0, buySignal, INDICATOR_DATA);
    SetIndexBuffer(1, sellSignal, INDICATOR_DATA);

    // Arrow codes: 233=up arrow (buy), 234=down arrow (sell)
    PlotIndexSetInteger(0, PLOT_ARROW, 233);
    PlotIndexSetInteger(1, PLOT_ARROW, 234);

    // Show arrows slightly offset from price
    PlotIndexSetDouble(0, PLOT_EMPTY_VALUE, 0);
    PlotIndexSetDouble(1, PLOT_EMPTY_VALUE, 0);

    return INIT_SUCCEEDED;
}

In your OnCalculate, set buySignal[i] = low[i] - 10*_Point when a buy condition is met (places arrow below the candle), and sellSignal[i] = high[i] + 10*_Point for sells (above the candle). Set to 0 (empty value) when no signal.

Separate Window Indicators

For oscillators and indicators that do not overlay on the price chart:

#property indicator_separate_window    // draw in separate sub-window
#property indicator_minimum 0          // fix Y-axis minimum
#property indicator_maximum 100        // fix Y-axis maximum
#property indicator_level1 30          // horizontal reference line
#property indicator_level2 70          // horizontal reference line
#property indicator_levelcolor clrSilver

Buffer Management Tips

  • Buffers used for drawing must come first, calculation-only buffers last
  • Use INDICATOR_CALCULATIONS for helper buffers that should not appear in the Data Window
  • Use PlotIndexSetDouble(index, PLOT_EMPTY_VALUE, 0) to define what "no data" looks like — the indicator skips drawing at those points
  • Set IndicatorSetString(INDICATOR_SHORTNAME, "Name") so your indicator shows a meaningful name in the chart and Data Window

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