def trace_roi(hemi, map_proj, closed=True, event_handlers=None, alternate_plots=None, **kw):
if event_handlers is None: event_handlers = {}<EOL>if alternate_plots is None: alternate_plots = []<EOL>if alternate_plots:<EOL><INDENT>pass<EOL><DEDENT>
trace_roi(hemi, map_proj) yields an ROIDrawer object that controls the tracing of lines around
  an ROI in a 2D matplotlib plot. After the ROI has been drawn in the plot, the resulting path
  trace can be obtained via the roi_drawer.trace object.

ROI tracing is very simple: any point in the plot is appended to the path as it is clicked; in
order to eliminate the previous point, hold shift while clicking. To end the path, hold control
while clicking. To abort the path, hold both shift and control while clicking. (Double-clicking
should be equivalent to control-clicking, but this does not work in all setups.) In order to use
the ROI tracing, `%matplotlib notebook` is recommended.

The trace_roi() function accepts all options that can be passed to cortex_plot() as well as the
following options:
  * closed (default: True) specifies whether the path-trace that is constructed should be closed
    (True) or open (False).
  * event_handlers (default: None) specifies additional event handlers (named by key) for the
    ROIDrawer().
  * alternate_plots (default: None) specifies a list of alternate plotting functions that must
    accept the axes as an argument (these are cycled with tab-click). Alternately, these may be
    matplotlib TriMesh objects that are simply made visible.