Raw rotary encoder support

kmk/common/rotary_encoder.py

@@ -0,0 +1,57 @@
+from kmk.common.pins import PULL_UP
+
+
+class RotaryEncoder:
+    # Please don't ask. I don't know. All I know is bit_value
+    # works as expected. Here be dragons, etc. etc.
+    MIN_VALUE = False + 1 << 1 | True + 1
+    MAX_VALUE = True + 1 << 1 | True + 1
+
+    def __init__(self, pos_pin, neg_pin):
+        self.pos_pin = pos_pin
+        self.neg_pin = neg_pin
+
+        self.pos_pin.switch_to_input(pull=PULL_UP)
+        self.neg_pin.switch_to_input(pull=PULL_UP)
+
+        self.prev_bit_value = self.bit_value()
+
+    def value(self):
+        return (self.pos_pin.value(), self.neg_pin.value())
+
+    def bit_value(self):
+        '''
+        Returns 2, 3, 5, or 6 based on the state of the rotary encoder's two
+        bits. This is a total hack but it does what we need pretty efficiently.
+        Shrug.
+        '''
+        return self.pos_pin.value() + 1 << 1 | self.neg_pin.value() + 1
+
+    def direction(self):
+        '''
+        Compares the current rotary position against the last seen position.
+
+        Returns True if we're rotating "positively", False if we're rotating "negatively",
+        and None if no change could safely be detected for any reason (usually this
+        means the encoder itself did not change)
+        '''
+        new_value = self.bit_value()
+        rolling_under = self.prev_bit_value == self.MIN_VALUE and new_value == self.MAX_VALUE
+        rolling_over = self.prev_bit_value == self.MAX_VALUE and new_value == self.MIN_VALUE
+        increasing = new_value > self.prev_bit_value
+        decreasing = new_value < self.prev_bit_value
+        self.prev_bit_value = new_value
+
+        if rolling_over:
+            return True
+        elif rolling_under:
+            return False
+
+        if increasing:
+            return True
+        if decreasing:
+            return False
+
+        # Either no change, or not a type of change we can safely detect,
+        # so safely do nothing
+        return None