【MQL4】ストキャスティクスの%Kと%Dがクロスした瞬間だけ矢印表示するインジケーターの作り方について解説してみた

//+------------------------------------------------------------------+
//|                                  StochasticCrossArrowIndicator.mq4 |
//|                     Copyright 2026, FX-EA System Project Creator |
//|                        https://creator.fx-ea-system-project.com/ |
//+------------------------------------------------------------------+
#property copyright "Copyright 2026, FX-EA System Project Creator"
#property link      "https://creator.fx-ea-system-project.com/"
#property version   "1.00"
#property strict
#property indicator_chart_window
#property indicator_buffers 2

input int  Kperiod       = 5;
input int  Dperiod       = 3;
input int  Slowing       = 3;
input int  PriceField    = 0;      // 0=Low/High基準、1=Close/Close基準
input bool FilterByZone  = false;  // trueなら買われすぎ・売られすぎ領域内のみ検知
input double OversoldLevel   = 20.0;
input double OverboughtLevel = 80.0;

double UpArrowBuffer[];
double DownArrowBuffer[];

int OnInit()
  {
   SetIndexBuffer(0, UpArrowBuffer);
   SetIndexStyle(0, DRAW_ARROW, STYLE_SOLID, 2, clrDodgerBlue);
   SetIndexArrow(0, 233);

   SetIndexBuffer(1, DownArrowBuffer);
   SetIndexStyle(1, DRAW_ARROW, STYLE_SOLID, 2, clrOrangeRed);
   SetIndexArrow(1, 234);

   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) ? prev_calculated - 1 : 1;

   for(int i = start; i < rates_total; i++)
     {
      int shift = rates_total - 1 - i;

      double kNow  = iStochastic(NULL, 0, Kperiod, Dperiod, Slowing, MODE_SMA, PriceField, MODE_MAIN, shift);
      double dNow  = iStochastic(NULL, 0, Kperiod, Dperiod, Slowing, MODE_SMA, PriceField, MODE_SIGNAL, shift);
      double kPrev = iStochastic(NULL, 0, Kperiod, Dperiod, Slowing, MODE_SMA, PriceField, MODE_MAIN, shift + 1);
      double dPrev = iStochastic(NULL, 0, Kperiod, Dperiod, Slowing, MODE_SMA, PriceField, MODE_SIGNAL, shift + 1);

      UpArrowBuffer[i]   = EMPTY_VALUE;
      DownArrowBuffer[i] = EMPTY_VALUE;

      bool crossUp   = (kPrev <= dPrev && kNow > dNow);
      bool crossDown = (kPrev >= dPrev && kNow < dNow);

      if(FilterByZone)
        {
         if(crossUp && kNow > OversoldLevel)
            crossUp = false;
         if(crossDown && kNow < OverboughtLevel)
            crossDown = false;
        }

      if(crossUp)
        {
         UpArrowBuffer[i] = low[i] - 10 * _Point;
        }
      else if(crossDown)
        {
         DownArrowBuffer[i] = high[i] + 10 * _Point;
        }
     }

   return(rates_total);
  }