Fix #130, fix #131, fix #189

This PR implements SnowPi, adds the ability for LEDBoard's to own other
LEDBoards as well as LEDs, and enhances blink so that manually
controlling a LED automatically stops it from blinking (no matter
whether it's blinking itself or a LEDBoard is blinking it).

It also fixes up RGBLED and Motor which I managed to break with the last
PR ...

gpiozero/output_devices.py

@@ -11,7 +11,7 @@ from threading import Lock
 from itertools import repeat, cycle, chain
 
 from .exc import OutputDeviceBadValue, GPIOPinMissing
-from .devices import GPIODevice, CompositeDevice, SourceMixin
+from .devices import GPIODevice, Device, CompositeDevice, SourceMixin
 from .threads import GPIOThread
 
 
@@ -121,6 +121,16 @@ class DigitalOutputDevice(OutputDevice):
         self._blink_thread = None
         super(DigitalOutputDevice, self).__init__(pin, active_high, initial_value)
         self._lock = Lock()
+        self._controller = None
+
+    @property
+    def value(self):
+        return self._read()
+
+    @value.setter
+    def value(self, value):
+        self._stop_blink()
+        self._write(value)
 
     def close(self):
         self._stop_blink()
@@ -174,6 +184,9 @@ class DigitalOutputDevice(OutputDevice):
             self._blink_thread = None
 
     def _stop_blink(self):
+        if self._controller:
+            self._controller._stop_blink(self)
+            self._controller = None
         if self._blink_thread:
             self._blink_thread.stop()
             self._blink_thread = None
@@ -286,6 +299,7 @@ class PWMOutputDevice(OutputDevice):
     """
     def __init__(self, pin=None, active_high=True, initial_value=0, frequency=100):
         self._blink_thread = None
+        self._controller = None
         if not 0 <= initial_value <= 1:
             raise OutputDeviceBadValue("initial_value must be between 0 and 1")
         super(PWMOutputDevice, self).__init__(pin, active_high)
@@ -437,6 +451,9 @@ class PWMOutputDevice(OutputDevice):
         )
 
     def _stop_blink(self):
+        if self._controller:
+            self._controller._stop_blink(self)
+            self._controller = None
         if self._blink_thread:
             self._blink_thread.stop()
             self._blink_thread = None
@@ -508,10 +525,10 @@ def _led_property(index, doc=None):
     return property(getter, setter, doc=doc)
 
 
-class RGBLED(SourceMixin, CompositeDevice):
+class RGBLED(SourceMixin, Device):
     """
-    Extends :class:`CompositeDevice` and represents a full color LED component
-    (composed of red, green, and blue LEDs).
+    Extends :class:`Device` and represents a full color LED component (composed
+    of red, green, and blue LEDs).
 
     Connect the common cathode (longest leg) to a ground pin; connect each of
     the other legs (representing the red, green, and blue anodes) to any GPIO
@@ -556,6 +573,18 @@ class RGBLED(SourceMixin, CompositeDevice):
     green = _led_property(1)
     blue = _led_property(2)
 
+    def close(self):
+        if self._leds:
+            self._stop_blink()
+            for led in self._leds:
+                led.close()
+            self._leds = ()
+        super(RGBLED, self).close()
+
+    @property
+    def closed(self):
+        return bool(self._leds)
+
     @property
     def value(self):
         """
@@ -569,6 +598,7 @@ class RGBLED(SourceMixin, CompositeDevice):
 
     @value.setter
     def value(self, value):
+        self._stop_blink()
         self.red, self.green, self.blue = value
 
     @property
@@ -606,11 +636,6 @@ class RGBLED(SourceMixin, CompositeDevice):
         r, g, b = self.value
         self.value = (1 - r, 1 - g, 1 - b)
 
-    def close(self):
-        self._stop_blink()
-        for led in self._leds:
-            led.close()
-
     def blink(
             self, on_time=1, off_time=1, fade_in_time=0, fade_out_time=0,
             on_color=(1, 1, 1), off_color=(0, 0, 0), n=None, background=True):
@@ -654,7 +679,8 @@ class RGBLED(SourceMixin, CompositeDevice):
             self._blink_thread.join()
             self._blink_thread = None
 
-    def _stop_blink(self):
+    def _stop_blink(self, led=None):
+        # If this is called with a single led, we stop all blinking anyway
         if self._blink_thread:
             self._blink_thread.stop()
             self._blink_thread = None
@@ -687,16 +713,19 @@ class RGBLED(SourceMixin, CompositeDevice):
                 cycle(sequence) if n is None else
                 chain.from_iterable(repeat(sequence, n))
                 )
+        for l in self._leds:
+            l._controller = self
         for value, delay in sequence:
-            self._leds[0].value, self._leds[1].value, self._leds[2].value = value
+            for l, v in zip(self._leds, value):
+                l._write(v)
             if self._blink_thread.stopping.wait(delay):
                 break
 
 
 class Motor(SourceMixin, CompositeDevice):
     """
-    Extends :class:`CompositeDevice` and represents a generic motor connected
-    to a bi-directional motor driver circuit (i.e.  an `H-bridge`_).
+    Extends :class:`CompositeDevice` and represents a generic motor
+    connected to a bi-directional motor driver circuit (i.e.  an `H-bridge`_).
 
     Attach an `H-bridge`_ motor controller to your Pi; connect a power source
     (e.g. a battery pack or the 5V pin) to the controller; connect the outputs
@@ -725,33 +754,9 @@ class Motor(SourceMixin, CompositeDevice):
             raise GPIOPinMissing(
                 'forward and backward pins must be provided'
             )
-        super(Motor, self).__init__()
-        self._forward = PWMOutputDevice(forward)
-        self._backward = PWMOutputDevice(backward)
-
-    def close(self):
-        self._forward.close()
-        self._backward.close()
-
-    @property
-    def closed(self):
-        return self._forward.closed and self._backward.closed
-
-    @property
-    def forward_device(self):
-        """
-        Returns the `PWMOutputDevice` representing the forward pin of the motor
-        controller.
-        """
-        return self._forward
-
-    @property
-    def backward_device(self):
-        """
-        Returns the `PWMOutputDevice` representing the backward pin of the
-        motor controller.
-        """
-        return self._backward
+        super(Motor, self).__init__(
+                forward_device=PWMOutputDevice(forward),
+                backward_device=PWMOutputDevice(backward))
 
     @property
     def value(self):
@@ -759,7 +764,7 @@ class Motor(SourceMixin, CompositeDevice):
         Represents the speed of the motor as a floating point value between -1
         (full speed backward) and 1 (full speed forward).
         """
-        return self._forward.value - self._backward.value
+        return self.forward_device.value - self.backward_device.value
 
     @value.setter
     def value(self, value):
@@ -788,8 +793,8 @@ class Motor(SourceMixin, CompositeDevice):
             The speed at which the motor should turn. Can be any value between
             0 (stopped) and the default 1 (maximum speed).
         """
-        self._backward.off()
-        self._forward.value = speed
+        self.backward_device.off()
+        self.forward_device.value = speed
 
     def backward(self, speed=1):
         """
@@ -799,8 +804,8 @@ class Motor(SourceMixin, CompositeDevice):
             The speed at which the motor should turn. Can be any value between
             0 (stopped) and the default 1 (maximum speed).
         """
-        self._forward.off()
-        self._backward.value = speed
+        self.forward_device.off()
+        self.backward_device.value = speed
 
     def reverse(self):
         """
@@ -814,5 +819,5 @@ class Motor(SourceMixin, CompositeDevice):
         """
         Stop the motor.
         """
-        self._forward.off()
-        self._backward.off()
+        self.forward_device.off()
+        self.backward_device.off()