Revamp Displayio and Add grayscale

.pylintrc

@@ -396,4 +396,4 @@ min-public-methods=1
 
 # Exceptions that will emit a warning when being caught. Defaults to
 # "Exception"
-overgeneral-exceptions=Exception
+overgeneral-exceptions=builtins.Exception

displayio/__init__.py

@@ -16,7 +16,7 @@
 * Author(s): Melissa LeBlanc-Williams
 
 """
-
+import threading
 from typing import Union
 from ._fourwire import FourWire
 from ._i2cdisplay import I2CDisplay
@@ -30,19 +30,68 @@
 from ._palette import Palette
 from ._shape import Shape
 from ._tilegrid import TileGrid
-from ._display import displays
 from ._displaybus import _DisplayBus
+from ._constants import CIRCUITPY_DISPLAY_LIMIT
 
 __version__ = "0.0.0+auto.0"
 __repo__ = "https://github.com/adafruit/Adafruit_Blinka_displayio.git"
 
 
+displays = []
+display_buses = []
+
+
+def _background():
+    """Main thread function to loop through all displays and update them"""
+    while True:
+        for display in displays:
+            display._background()  # pylint: disable=protected-access
+
+
 def release_displays() -> None:
     """Releases any actively used displays so their busses and pins can be used again.
 
     Use this once in your code.py if you initialize a display. Place it right before the
     initialization so the display is active as long as possible.
     """
-    for _disp in displays:
-        _disp._release()  # pylint: disable=protected-access
+    for display in displays:
+        display._release()  # pylint: disable=protected-access
     displays.clear()
+
+    for display_bus in display_buses:
+        display_bus.deinit()
+    display_buses.clear()
+
+
+def allocate_display(new_display: Union[Display, EPaperDisplay]) -> None:
+    """Add a display to the displays pool and return the new display"""
+    if len(displays) >= CIRCUITPY_DISPLAY_LIMIT:
+        raise RuntimeError("Too many displays")
+    displays.append(new_display)
+
+
+def allocate_display_bus(new_display_bus: _DisplayBus) -> None:
+    """Add a display bus to the display_buses pool and return the new display bus"""
+    if len(display_buses) >= CIRCUITPY_DISPLAY_LIMIT:
+        raise RuntimeError(
+            "Too many display busses; forgot displayio.release_displays() ?"
+        )
+    display_buses.append(new_display_bus)
+
+
+background_thread = threading.Thread(target=_background, daemon=True)
+
+
+# Start the background thread
+def _start_background():
+    if not background_thread.is_alive():
+        background_thread.start()
+
+
+def _stop_background():
+    if background_thread.is_alive():
+        # Stop the thread
+        background_thread.join()
+
+
+_start_background()

displayio/_area.py

@@ -25,9 +25,9 @@
 
 
 class Area:
-    # pylint: disable=invalid-name,missing-function-docstring
-    """Area Class to represent an area to be updated. Currently not used."""
+    """Area Class to represent an area to be updated."""
 
+    # pylint: disable=invalid-name
     def __init__(self, x1: int = 0, y1: int = 0, x2: int = 0, y2: int = 0):
         self.x1 = x1
         self.y1 = y1
@@ -38,25 +38,29 @@ def __init__(self, x1: int = 0, y1: int = 0, x2: int = 0, y2: int = 0):
     def __str__(self):
         return f"Area TL({self.x1},{self.y1}) BR({self.x2},{self.y2})"
 
-    def _copy_into(self, dst) -> None:
+    def copy_into(self, dst) -> None:
+        """Copy the area into another area."""
         dst.x1 = self.x1
         dst.y1 = self.y1
         dst.x2 = self.x2
         dst.y2 = self.y2
 
-    def _scale(self, scale: int) -> None:
+    def scale(self, scale: int) -> None:
+        """Scale the area by scale."""
         self.x1 *= scale
         self.y1 *= scale
         self.x2 *= scale
         self.y2 *= scale
 
-    def _shift(self, dx: int, dy: int) -> None:
+    def shift(self, dx: int, dy: int) -> None:
+        """Shift the area by dx and dy."""
         self.x1 += dx
         self.y1 += dy
         self.x2 += dx
         self.y2 += dy
 
-    def _compute_overlap(self, other, overlap) -> bool:
+    def compute_overlap(self, other, overlap) -> bool:
+        """Compute the overlap between two areas. Returns True if there is an overlap."""
         a = self
         overlap.x1 = max(a.x1, other.x1)
         overlap.x2 = min(a.x2, other.x2)
@@ -69,22 +73,24 @@ def _compute_overlap(self, other, overlap) -> bool:
 
         return overlap.y1 < overlap.y2
 
-    def _empty(self):
+    def empty(self):
+        """Return True if the area is empty."""
         return (self.x1 == self.x2) or (self.y1 == self.y2)
 
-    def _canon(self):
+    def canon(self):
+        """Make sure the area is in canonical form."""
         if self.x1 > self.x2:
             self.x1, self.x2 = self.x2, self.x1
         if self.y1 > self.y2:
             self.y1, self.y2 = self.y2, self.y1
 
-    def _union(self, other, union):
-        # pylint: disable=protected-access
-        if self._empty():
-            self._copy_into(union)
+    def union(self, other, union):
+        """Combine this area along with another into union"""
+        if self.empty():
+            self.copy_into(union)
             return
-        if other._empty():
-            other._copy_into(union)
+        if other.empty():
+            other.copy_into(union)
             return
 
         union.x1 = min(self.x1, other.x1)
@@ -93,12 +99,15 @@ def _union(self, other, union):
         union.y2 = max(self.y2, other.y2)
 
     def width(self) -> int:
+        """Return the width of the area."""
         return self.x2 - self.x1
 
     def height(self) -> int:
+        """Return the height of the area."""
         return self.y2 - self.y1
 
     def size(self) -> int:
+        """Return the size of the area."""
         return self.width() * self.height()
 
     def __eq__(self, other):
@@ -113,14 +122,15 @@ def __eq__(self, other):
         )
 
     @staticmethod
-    def _transform_within(
+    def transform_within(
         mirror_x: bool,
         mirror_y: bool,
         transpose_xy: bool,
         original: Area,
         whole: Area,
         transformed: Area,
     ):
+        """Transform an area within a larger area."""
         # pylint: disable=too-many-arguments
         # Original and whole must be in the same coordinate space.
         if mirror_x: