Merge pull request #172 from waveform80/led-board-pwm-blink

Re: #94 and #161

gpiozero/boards.py

@@ -11,7 +11,7 @@ except ImportError:
 
 from time import sleep
 from collections import namedtuple
-from itertools import repeat
+from itertools import repeat, cycle, chain
 
 from .exc import InputDeviceError, OutputDeviceError
 from .input_devices import Button
@@ -102,18 +102,30 @@ class LEDBoard(SourceMixin, CompositeDevice):
         for led in self.leds:
             led.toggle()
 
-    def blink(self, on_time=1, off_time=1, n=None, background=True):
+    def blink(
+            self, on_time=1, off_time=1, fade_in_time=0, fade_out_time=0,
+            n=None, background=True):
         """
         Make all the LEDs turn on and off repeatedly.
 
         :param float on_time:
-            Number of seconds on
+            Number of seconds on. Defaults to 1 second.
 
         :param float off_time:
-            Number of seconds off
+            Number of seconds off. Defaults to 1 second.
+
+        :param float fade_in_time:
+            Number of seconds to spend fading in. Defaults to 0. Must be 0 if
+            ``pwm`` was ``False`` when the class was constructed
+            (:exc:`ValueError` will be raised if not).
+
+        :param float fade_out_time:
+            Number of seconds to spend fading out. Defaults to 0. Must be 0 if
+            ``pwm`` was ``False`` when the class was constructed
+            (:exc:`ValueError` will be raised if not).
 
         :param int n:
-            Number of times to blink; ``None`` means forever
+            Number of times to blink; ``None`` (the default) means forever.
 
         :param bool background:
             If ``True``, start a background thread to continue blinking and
@@ -121,9 +133,15 @@ class LEDBoard(SourceMixin, CompositeDevice):
             finished (warning: the default value of *n* will result in this
             method never returning).
         """
+        if isinstance(self.leds[0], LED):
+            if fade_in_time:
+                raise ValueError('fade_in_time must be 0 with non-PWM LEDs')
+            if fade_out_time:
+                raise ValueError('fade_out_time must be 0 with non-PWM LEDs')
         self._stop_blink()
         self._blink_thread = GPIOThread(
-            target=self._blink_leds, args=(on_time, off_time, n)
+            target=self._blink_leds,
+            args=(on_time, off_time, fade_in_time, fade_out_time, n)
         )
         self._blink_thread.start()
         if not background:
@@ -135,17 +153,29 @@ class LEDBoard(SourceMixin, CompositeDevice):
             self._blink_thread.stop()
             self._blink_thread = None
 
-    def _blink_leds(self, on_time, off_time, n):
-        iterable = repeat(0) if n is None else repeat(0, n)
-        for i in iterable:
+    def _blink_leds(self, on_time, off_time, fade_in_time, fade_out_time, n, fps=50):
+        sequence = []
+        if fade_in_time > 0:
+            sequence += [
+                (i * (1 / fps) / fade_in_time, 1 / fps)
+                for i in range(int(fps * fade_in_time))
+                ]
+        sequence.append((1, on_time))
+        if fade_out_time > 0:
+            sequence += [
+                (1 - (i * (1 / fps) / fade_out_time), 1 / fps)
+                for i in range(int(fps * fade_out_time))
+                ]
+        sequence.append((0, off_time))
+        sequence = (
+                cycle(sequence) if n is None else
+                chain.from_iterable(repeat(sequence, n))
+                )
+        for value, delay in sequence:
             for led in self.leds:
-                led.on()
-            if self._blink_thread.stopping.wait(on_time):
-                break            
-            for led in self.leds:
-                led.off()
-            if self._blink_thread.stopping.wait(off_time):
-                break            
+                led.value = value
+            if self._blink_thread.stopping.wait(delay):
+                break
 
 
 class PiLiter(LEDBoard):