performance: implement growing sparkline

Author: bablokb

adafruit_display_shapes/sparkline.py

@@ -54,18 +54,25 @@ class Sparkline(displayio.Group):
  :param width: Width of the sparkline graph in pixels
  :param height: Height of the sparkline graph in pixels
  :param max_items: Maximum number of values housed in the sparkline
+ :param dyn_xpitch: dynamically change xpitch (True)
  :param y_min: Lower range for the y-axis. Set to None for autorange.
  :param y_max: Upper range for the y-axis. Set to None for autorange.
  :param x: X-position on the screen, in pixels
  :param y: Y-position on the screen, in pixels
  :param color: Line color, the default value is 0xFFFFFF (WHITE)
+
+ Note: If dyn_xpitch is True (default), the sparkline will allways span
+ the complete width. Otherwise, the sparkline will grow when you
+ add values. Once the line has reached the full width, the sparkline
+ will scroll to the left.
  """
 
  def __init__(
  self,
  width: int,
  height: int,
  max_items: int,
+ dyn_xpitch: Optional[bool] = True, # True = dynamic pitch size
  y_min: Optional[int] = None, # None = autoscaling
  y_max: Optional[int] = None, # None = autoscaling
  x: int = 0,
@@ -79,6 +86,9 @@ def __init__(
  self.color = color #
  self._max_items = max_items # maximum number of items in the list
  self._spark_list = [] # list containing the values
+ self.dyn_xpitch = dyn_xpitch
+ if not dyn_xpitch:
+ self._xpitch = (width - 1) / (self._max_items - 1)
  self.y_min = y_min # minimum of y-axis (None: autoscale)
  self.y_max = y_max # maximum of y-axis (None: autoscale)
  self.y_bottom = y_min
@@ -89,6 +99,7 @@ def __init__(
  # updated if autorange
  self._x = x
  self._y = y
+ self._redraw = True # _redraw: redraw primitives
 
  super().__init__(x=x, y=y) # self is a group of lines
 
@@ -98,6 +109,7 @@ def clear_values(self) -> None:
  for _ in range(len(self)): # remove all items from the current group
  self.pop()
  self._spark_list = [] # empty the list
+ self._redraw = True
 
  def add_value(self, value: float, update: bool = True) -> None:
  """Add a value to the sparkline.
@@ -114,7 +126,22 @@ def add_value(self, value: float, update: bool = True) -> None:
  len(self._spark_list) >= self._max_items
  ): # if list is full, remove the first item
  self._spark_list.pop(0)
+ self._redraw = True
  self._spark_list.append(value)
+
+ if self.y_min is None:
+ self._redraw = self._redraw or value < self.y_bottom
+ self.y_bottom = (
+ value if not self.y_bottom else min(value, self.y_bottom)
+ )
+ if self.y_max is None:
+ self._redraw = self._redraw or value > self.y_top
+ self.y_top = value if not self.y_top else max(value, self.y_top)
+
+ # Guard for y_top and y_bottom being the same
+ if self.y_top == self.y_bottom:
+ self.y_bottom *= 0.99
+
  if update:
  self.update()
 
@@ -146,107 +173,109 @@ def _plotline(
  last_value: float,
  x_2: int,
  value: float,
- y_bottom: int,
- y_top: int,
  ) -> None:
 
- y_2 = int(self.height * (y_top - value) / (y_top - y_bottom))
- y_1 = int(self.height * (y_top - last_value) / (y_top - y_bottom))
+ y_2 = int(self.height * (self.y_top - value) / (self.y_top - self.y_bottom))
+ y_1 = int(
+ self.height * (self.y_top - last_value) / (self.y_top - self.y_bottom)
+ )
  self.append(Line(x_1, y_1, x_2, y_2, self.color)) # plot the line
+ self._last = [x_2, value]
 
  # pylint: disable= too-many-branches, too-many-nested-blocks
 
  def update(self) -> None:
  """Update the drawing of the sparkline."""
 
- # get the y range
- if self.y_min is None:
-  self.y_bottom = min(self._spark_list)
- else:
- self.y_bottom = self.y_min
+ # bail out early if we only have a single point
+ n_points = len(self._spark_list)
+ if n_points < 2:
+  self._last = [0, self._spark_list[0]]
+ return
 
- if self.y_max is None:
- self.y_top = max(self._spark_list)
+ if self.dyn_xpitch:
+ # this is a float, only make int when plotting the line
+ xpitch = (self.width - 1) / (n_points - 1)
+ self._redraw = True
  else:
- self.y_top = self.y_max
-
- # Guard for y_top and y_bottom being the same
- if self.y_top == self.y_bottom:
- self.y_bottom -= 10
- self.y_top += 10
-
- if len(self._spark_list) > 2:
- xpitch = (self.width - 1) / (
- len(self._spark_list) - 1
- ) # this is a float, only make int when plotting the line
-
- for _ in range(len(self)): # remove all items from the current group
- self.pop()
-
- for count, value in enumerate(self._spark_list):
- if count == 0:
- pass # don't draw anything for a first point
- else:
- x_2 = int(xpitch * count)
- x_1 = int(xpitch * (count - 1))
-
- if (self.y_bottom <= last_value <= self.y_top) and (
- self.y_bottom <= value <= self.y_top
- ): # both points are in range, plot the line
- self._plotline(
- x_1, last_value, x_2, value, self.y_bottom, self.y_top
- )
-
- else: # at least one point is out of range, clip one or both ends the line
- if ((last_value > self.y_top) and (value > self.y_top)) or (
- (last_value < self.y_bottom) and (value < self.y_bottom)
- ):
- # both points are on the same side out of range: don't draw anything
+ xpitch = self._xpitch
+
+ # only add new segment if redrawing is not necessary
+ if not self._redraw:
+ # end of last line (last point, read as "x(-1)")
+ x_m1 = self._last[0]
+ y_m1 = self._last[1]
+ # end of new line (new point, read as "x(0)")
+ x_0 = int(x_m1 + xpitch)
+ y_0 = self._spark_list[-1]
+ self._plotline(x_m1, y_m1, x_0, y_0)
+ return
+
+ self._redraw = False # reset, since we now redraw everything
+ for _ in range(len(self)): # remove all items from the current group
+ self.pop()
+
+ for count, value in enumerate(self._spark_list):
+ if count == 0:
+ pass # don't draw anything for a first point
+ else:
+ x_2 = int(xpitch * count)
+ x_1 = int(xpitch * (count - 1))
+
+ if (self.y_bottom <= last_value <= self.y_top) and (
+ self.y_bottom <= value <= self.y_top
+ ): # both points are in range, plot the line
+ self._plotline(x_1, last_value, x_2, value)
+
+ else: # at least one point is out of range, clip one or both ends the line
+ if ((last_value > self.y_top) and (value > self.y_top)) or (
+ (last_value < self.y_bottom) and (value < self.y_bottom)
+ ):
+ # both points are on the same side out of range: don't draw anything
+ pass
+ else:
+ xint_bottom = self._xintercept(
+ x_1, last_value, x_2, value, self.y_bottom
+ ) # get possible new x intercept points
+ xint_top = self._xintercept(
+ x_1, last_value, x_2, value, self.y_top
+ ) # on the top and bottom of range
+ if (xint_bottom is None) or (
+ xint_top is None
+ ): # out of range doublecheck
  pass
  else:
- xint_bottom = self._xintercept(
- x_1, last_value, x_2, value, self.y_bottom
- ) # get possible new x intercept points
- xint_top = self._xintercept(
- x_1, last_value, x_2, value, self.y_top
- ) # on the top and bottom of range
-
- if (xint_bottom is None) or (
- xint_top is None
- ): # out of range doublecheck
- pass
- else:
- # Initialize the adjusted values as the baseline
- adj_x_1 = x_1
- adj_last_value = last_value
- adj_x_2 = x_2
- adj_value = value
-
- if value > last_value: # slope is positive
- if xint_bottom >= x_1: # bottom is clipped
- adj_x_1 = xint_bottom
- adj_last_value = self.y_bottom # y_1
- if xint_top <= x_2: # top is clipped
- adj_x_2 = xint_top
- adj_value = self.y_top # y_2
- else: # slope is negative
- if xint_top >= x_1: # top is clipped
- adj_x_1 = xint_top
- adj_last_value = self.y_top # y_1
- if xint_bottom <= x_2: # bottom is clipped
- adj_x_2 = xint_bottom
- adj_value = self.y_bottom # y_2
-
- self._plotline(
- adj_x_1,
- adj_last_value,
- adj_x_2,
- adj_value,
- self.y_bottom,
- self.y_top,
- )
-
- last_value = value # store value for the next iteration
+ # Initialize the adjusted values as the baseline
+ adj_x_1 = x_1
+ adj_last_value = last_value
+ adj_x_2 = x_2
+ adj_value = value
+
+ if value > last_value: # slope is positive
+ if xint_bottom >= x_1: # bottom is clipped
+ adj_x_1 = xint_bottom
+ adj_last_value = self.y_bottom # y_1
+ if xint_top <= x_2: # top is clipped
+ adj_x_2 = xint_top
+ adj_value = self.y_top # y_2
+ else: # slope is negative
+ if xint_top >= x_1: # top is clipped
+ adj_x_1 = xint_top
+ adj_last_value = self.y_top # y_1
+ if xint_bottom <= x_2: # bottom is clipped
+ adj_x_2 = xint_bottom
+ adj_value = self.y_bottom # y_2
+
+ self._plotline(
+ adj_x_1,
+ adj_last_value,
+ adj_x_2,
+ adj_value,
+ self.y_bottom,
+ self.y_top,
+ )
+
+ last_value = value # store value for the next iteration
 
  def values(self) -> List[float]:
  """Returns the values displayed on the sparkline."""