MT4: How to plot existing data under the price chart as an indicator?

Question

I have some COT data that I want to plot under the main price window as an indicator. The COT data are external data, i.e. independent of the prices. So one can not write it like a traditional indicator calculated from the prices. Since I have all the data needed, I don't need to do any calculation. I only need to convert the date and time so that it aligns with the price chart. I will figure out how to do it later. Now, if we ignore the alignment, what I want to ask is how could I plot the data under the price chart? Thanks!

Answer 1

Alternative A:

Use the MT4-GUI tools and plot the data programmatically right into the MT4.Graph or using the screen-layout-plane of GUI-objects, independent of the underlying live-[TimeDOMAIN,PriceDOMAIN]-graphing, both using Expert Advisor-type of MQL4-code. We use this approach most often for all the tasks, that would normally land as a Custom Indicator-type of MQL4-code, as the New-MQL4.56789 code-execution engine has reduced the achievable performance for all ( yes, ALL ) Custom Indicator code-units' execution into a single, thus both RealTime-sensitive and potentially blocking, thread.

Using this alternative, you retain the full freedom of the code-design and may benefit a lot from pre-computing & pre-setting the GUI-objects inside OnInit(){...} section, before entering the trading-loop. This also minimises the latency costs associated with a need to update the GUI-scene from inside an OnTick(){...} event-loop.

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Alternative B:

One may also opt to do a similar job using an independent Script-type of MQL4-code unit, as the COT data are weekly announced and thus static per-se.

Launching Script is a step, that can happen whenever feasible and this implementation model may also enjoy some ex-post modification tools, that could be run from another Expert Advisor or another Script MQL4-code, for the sake for some ex-post live-GUI-scene modification/maintenance.

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Alternative C:

If one indeed insists to do so, the GUI-composition might be assembled inside a rather special-purpose live-calculated Custom Indicator-type of MQL4-code.

This approach but has to carefully deploy the GUI-composition into the Custom Indicator OnInit(){...} section and avoid any risk of blocking a flow of execution inside the above said critical section of OnCalculate(){...}.

Buffer-mapped, register-based Custom Indicator data & graphing tools are rather rigid for more advanced purposes, that do not strictly follow the hard-wired logic of a code, responding just to a stream of MarketEvent-s, which may, but need not, happen at once, but is being arranged by a sort of mini-batches, so as to process the whole depth of the DataStore in a segmented ( thus less-blocking ) processing approach.

Building the GUI-scene inside the OnInit() section of the Custom Indicator, one may still benefit from distributed processing, if external data source is to be read and/or any similar type inter-platform communications ( be it for a messaging or a signalling purpose ).

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My choice would be the [A]

Mapping { Date, Time } onto a MQL4-datetime is trivial, MQL4 used to use since its beginning datetime as int seconds elapsed since 1970-01-01,00:00:00.000 - so simple, so easy.

Answer 2

declare the indicator buffer:

double ExtBufferCOT[];

assign indexes of buffers

SetIndexStyle(  0, DRAW_LINE    );
SetIndexBuffer( 0, ExtBufferCOT );

in the OnCalculate() function - make sure it is time to check the levels again ( I think you do not need to update them every tick, right? Maybe once a day or once a week) and then read the file that you have ( we do not have example of file so senseless to describe how to do that here ), convert elements of the file, using StrToTime() and StrToDouble() the last step - get last N lines from your file, and map them to the indicator buffers:

double       value;
datetime     time;                      // - your values from file are here

int          shift  = iBarShift( _Symbol, 0, time );
ExtBufferCOT[shift] = value;            /* probably need to fill buffer
                                           of next candles too
                                           if your chart timeframe
                                           is smaller then frequency
                                           of observations in the file
                                           */