base class and quadratic easing functions

Author: semitable

easing-functions/__init__.py renamed to easing_functions/__init__.py

@@ -0,0 +1,45 @@
+
+class EasingBase:
+    limit = (-1, 1)
+
+    def __init__(self, start=0, end=1, duration=1):
+        self.start = start
+        self.end = end
+        self.duration = duration
+
+    @classmethod
+    def func(cls, t):
+        raise NotImplementedError
+
+    def ease(self, alpha):
+        """
+        Interpolate between start and end given an alpha from 0 to duration
+        :param alpha: 0 to duration
+        :return: respective value between start and end
+        """
+        t = self.limit[0] * (1 - alpha) + self.limit[1] * alpha
+        t /=self.duration
+        a = self.func(t)
+        return self.end * a + self.start * (1 - a)
+
+
+"""
+Quadratic easing functions
+"""
+
+
+class QuadEaseInOut(EasingBase):
+    limit = (-1, 1)
+
+    def func(self, t):
+        if t < 0:
+            return (t + 1) ** 2 / (self.limit[1] - self.limit[0])
+        return -(t - 1) ** 2 / (self.limit[1] - self.limit[0]) + 1
+
+
+class QuadEaseIn(QuadEaseInOut):
+    limit = (-1, 0)
+
+
+class QuadEaseOut(QuadEaseInOut):
+    limit = (0, 1)