[amibroker] Custom Backtester Code for Forex Slippage

[ozzyapeman]

Hi. I am hoping anyone out there can check this code and perhaps give me
some pointers on how to do the actual scaling up and down of the exit
prices?

To mimic a more realistic backtesting model for trading Forex, I want to
scale the backtester's exit prices down 2 pips if a Sell and up 2 pips
if a Cover. My actual trade system has a 1-bar trade delay so not sure
how that affects the below code.  I added a generic trade system to the
below code for the sake of simplicity.

Is this the correct approach? Or do I need to add some custom metrics?
I'm not too sure if this approach is the right way. And I'm still
missing the meat and potatoes - in the two "ADD CODE HERE" sections:

// Custom Backtester Code to add Slippage to Forex trades
//
// We Sell and Cover on Open.
// But we want actual Sell prices to be slipped down by 2 pips and
// actual Cover prices to be slipped up by 2 pips.

// First we need to enable custom backtest procedure AND
// tell AmiBroker to use current formula

SetCustomBacktestProc("");

// Now custom-backtest procedure follows

if( Status("action") == actionPortfolio )
{
     bo = GetBacktesterObject();

     bo.Backtest(1); // run default backtest procedure

//  iterate through closed trades first

    for( trade = bo.GetFirstTrade(); trade; trade = bo.GetNextTrade() )
    {
           if( sig.IsLong() AND sig.IsExit() )  //check if the signal is
a Sell of a Long position
          {
             // ADD CODE HERE: NEED TO REDUCE THE SELL EXIT PRICE BY
0.0002
           }

        if( NOT sig.IsLong() AND sig.IsExit() )  //check if the signal is
a Cover of a Short position
          {
             // ADD CODE HERE: NEED TO INCREASE THE COVER EXIT PRICE BY
0.0002
           }
    }
}

// your trading system here

fast = Optimize( "fast", 12, 5, 20, 1  );
slow = Optimize( "slow", 26, 10, 25, 1  );
Buy=Cross( MACD( fast,slow ),Signal( fast,slow ) );
Sell=Cross( Signal( fast,slow ),MACD( fast,slow ) );
BuyPrice = SellPrice = ShortPrice = CoverPrice = Open;