fixes #264

Author: prjemian

CHANGES.rst

@@ -6,6 +6,9 @@ Change History
 
 :1.1.16:  expected by *tba* : 
 
+    * `#264 <https://github.com/prjemian/spec2nexus/issues/264>`_
+       Limit number of traces shown on a plot - use a FIFO
+
 :1.1.15:  expected by *2019-11-21* : bug fixes, adds asyn record support
 
     * `#259 <https://github.com/prjemian/spec2nexus/issues/259>`_

apstools/utils.py

@@ -3,6 +3,7 @@
 
 .. autosummary::
    
+   ~becplot_prune_fifo
    ~cleanupText
    ~command_list_as_table
    ~connect_pvlist
@@ -76,6 +77,45 @@
 class ExcelReadError(xlrd.XLRDError): ...
 
 
+def becplot_prune_fifo(n, y, x):
+    """
+    find the plot with axes x and y and replot with only the last *n* lines
+
+    Note: this is not a bluesky plan.  Call it as normal Python function.
+
+    EXAMPLE::
+
+        becplot_prune_fifo(1, noisy, m1)
+
+    PARAMETERS
+    
+    n : int
+        number of plots to keep
+    
+    y : object
+        ophyd Signal object on dependent (y) axis
+    
+    x : object
+        ophyd Signal object on independent (x) axis
+    
+    Assumes object `bec` (instance of BestEffortCallback) is defined.
+    """
+    global bec
+    for liveplot in bec._live_plots.values():
+        lp = liveplot.get(y.name)
+        if lp is None:
+            logging.debug(f"no LivePlot with name {y.name}")
+            continue
+        if lp.x != x.name or lp.y != y.name:
+            logging.debug(f"no LivePlot with axes ('{x.name}', '{y.name}')")
+            continue
+        if len(lp.ax.lines) > n:
+            logging.debug(f"limiting LivePlot({y.name}) to {n} traces")
+            lp.ax.lines = lp.ax.lines[-n:]
+            lp.update_plot()
+
+
+
 def cleanupText(text):
     """
     convert text so it can be used as a dictionary key