[GT] Re: BuySellArrows.pm Trigger Prices

[Chia-liang Kao <clkao AT clkao.org>]

Jon.

2009/11/12 Jon Edwards <fornews
AT
hotmail.com>:
> Using graphic.pl and specifying the below add line for BuySellArrows.pm I
> get the arrows as expected.
> What I'd also like to see is the price at which that was triggered; in this
> case it would be when those EMAs cross. Looking at the code I'm having
> trouble trying to understand a couple of things.

If you have a S:Generic-based trigger, the signal is always determined
at the end of the bar, and drawing the arrow near the CLOSE of the bar
should be close enough.  What you describe might be more interesting
if you have a ChannelBreakout based trigger, where the triggering
price might not be the end of the bar, and to show this on the chart
you'll need to modify BuySellArrow to accept another price data source
and render the arrows accordingly, which is slightly complicated.
(this answers (2))

> 1) The basic flow from BuySellArrows.pm to invoking e.g. CrossOverUp.pm.
> Does BuySellArrows.pm invoke Generic.pm which in turn invokes CrossOverUp.pm
> ? I'm just not seeing this flow yet.

IIRC all the graph objects are expecting some kind of DataSource, in
this cause it's the system's signal, which is a generic crossoverup
signal.

> 2) There seems to be 2 main structures passed around :Â self and calc.
> CrossOverUp.pm seems to use calc for determining the trigger/arrow price but
> how to get that known in BuySellArrows.pm
>
> --add=BuySellArrows(Systems::Generic {S::Generic::CrossOverUp {I:EMA 3}
> {I:EMA 7}} {S::Generic::CrossOverDown {I:EMA 3} {I:EMA 7}} )
>
> Thank you,
> Jon
>
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