selectively update lines in add_values

`add_values` would repeatedly call `update` for each line where a value was added, and `update` calls `_draw` which re-draws _all_ lines each time it is called.

By keeping track of lines that need to be updated and only calling `update` once at the end of `add_values`, we avoid $(n-1)^2$ spurious line re-draws.

Author: Karel-Kroeze

adafruit_display_shapes/multisparkline.py

@@ -172,8 +172,10 @@ def add_values(self, values: List[float], update: bool = True) -> None:
         call the update()-method
         """
 
+        lines_to_update = []
         for i, value in enumerate(values):
             if value is not None:
+                lines_to_update.append(i)
                 top = self.y_tops[i]
                 bottom = self.y_bottoms[i]
                 if (
@@ -195,8 +197,8 @@ def add_values(self, values: List[float], update: bool = True) -> None:
                 self.y_tops[i] = top
                 self.y_bottoms[i] = bottom
 
-                if update:
-                    self.update_line(i)
+        if update and lines_to_update:
+            self.update_line(lines_to_update)
 
     def _add_point(
         self,