Our first major UI "mode" (yes kinda like the modes in emacs) that has
handles to a client side order book api, line and arrow editors, and
interacts with a spawned `emsd` (the EMS daemon actor).
Buncha cleaning and fixes in here for various thingers as well.
Since the "crosshair" is growing more and more UX implementation details
it probably makes sense to call it what it is; a python level mouse
abstraction. Add 2 internal sets: `_hovered` for allowing mouse hovered
objects to register themselves to other cursor aware components, and
`_trackers` for allowing scene items to "track" cursor movements via
a `on_tracked_source()` callback.
Support tracking the mouse cursor using a new `on_tracked_sources()`
callback method. Make hovered highlight a bit thicker and highlight when
click-dragged. Add a delete method for removing from the scene along
with label.
Leverages `QGraphicsItem.cacheMode` to speed up interactivity via
less `.paint()` calls (on mouse interaction) and redraws of the
underlying path when there are no transformations (other then a shift).
In order to keep the "flat bar on new time period" UX, a couple special
methods have to be triggered to get a redraw of the pixel buffer when
appending new data.
Use `QPainterPath.controlPointRect()` over `.boundingRect()` since
supposedly it's a lot faster. Drop all use of `QPicture` (since it seems
to conflict with the pixel buffer stuff?) and it doesn't give any
measurable speedup when drawing the "last bar" lines.
Oh, and add some profiling for now.
Tyler Goodlet
goodboy