When exiting a pp toward net-zero, we may sometimes run into the issue
of having a "fractional slot" worth of units in allocator limit terms.
This is further nuanced by live orders which are submitted above the
current clearing price which get allocated a size (based on that staged
but non-cleared price) according to their limit size unit which can be
calculated to be less then the size that would have been allocated at
the actual clearing price. In the short term cope with this discrepancy
by simply using a "slot and a half" as the decision point of whether to
exit a slot's worth or the remaining pp's worth of units. In other words
if you can exit 1.5x a slot's worth or less, exit the remaining pp,
otherwise exit a slot's worth. This is a stop gap until we have a better
solution to limiting staged orders to (some range around) the currently
computed clear-able price.
We need a subtask to compute the current pp PnL in real-time but really
only if a pp exists - a spawnable subtask would be ideal for this. Stage
a tick streaming task using a stream bcaster; no actual pnl calc yet.
Since we're going to need subtasks anyway might as well stick the order
mode UI processing loop in a task as well and then just give the whole
thing a ctx mngr api. This'll probably be handy for when we have
auto-strats that need to dynamically use the mode's api as well.
Oh, and move the time -> index mapper to a chart method for now.
Use this method to go through writing all allocator parameters and then
reading all changes back into the order mode pane including updating the
limit and step labels by the fill bar.
Machinery changes:
- add `.limit()` and `.step_sizes()` methods to the allocator to
provide the appropriate data depending on the pp limit size unit (eg.
currency vs. units)
- humanize the label display text such that you have nice suffixes and
a fixed precision
- tweak the fill bar labels to be simpler since the values are now
humanized
- expect `.on_ui_settings_change()` to be called for every slots hotkey
tweak
Turned out to be pretty simple, on every pp update just recompute
the proportion of slots used based on the limit size units.
Don't assign the allocator callback method for alert lines since
there's no size to generate. Move from-existing-pp calculations
into the order pane itself.
Handling the edge cases in this was "fun", namely:
- entering with less then a slot's worth of units to purchase
before hitting the pp limit or, less then a slots worth when exiting
toward a net-zero position.
- round pp msg updates using the symbol tick and lot size digits to
avoid super small (1e-30 lel) positions lingering in the ems (happens
moreso with the paper engine).
- don't expect the next size method to be called for alert level changes
Tyler Goodlet