Match MC bezier interpolation for degenerate cases

Don't preform handle scaling and clamping
Add tests for keyframe interpolation

src/aaf2/interpolation.py

@@ -147,26 +147,29 @@ def scale_handle(p0, p1, p2):
     y = (p1[1] - p0[1]) * (p2[0] - p0[0]) / (p1[0] - p0[0])
     return [p2[0], p0[1] + y]
 
-def bezier_interpolate(p0, p1, p2, p3, x):
+def bezier_interpolate(p0, p1, p2, p3, x, scale_handles=False):
 
     # degenerate cases 1
     # p0 is after p3
     if p0[0] >= p3[0]:
-        return p[1]
-
-    # degenerate cases 2
-    # p1 after p3 or before p0
-    if p1[0] > p3[0]:
-        p1 = scale_handle(p0, p1, p3)
-    elif p1[0] < p0[0]:
-        p1 = [p0[0], p1[1]]
-
-    # degenerate cases 3
-    # p2 before p0 or after p3
-    if p2[0] < p0[0]:
-        p2 = scale_handle(p3, p2, p0)
-    elif p2[0] > p3[0]:
-        p2 = [p3[0], p2[1]]
+        return p0[1]
+
+    # Media Composer doesn't perform any scaling or clamping of handles
+    # if their x positions are out not between p0.x and p3.x.
+    if scale_handles:
+        # degenerate cases 2
+        # p1 after p3 or before p0
+        if p1[0] > p3[0]:
+            p1 = scale_handle(p0, p1, p3)
+        elif p1[0] < p0[0]:
+            p1 = [p0[0], p1[1]]
+
+        # degenerate cases 3
+        # p2 before p0 or after p3
+        if p2[0] < p0[0]:
+            p2 = scale_handle(p3, p2, p0)
+        elif p2[0] > p3[0]:
+            p2 = [p3[0], p2[1]]
 
     # offset points so x is the x axis
     pa = p0[0] - x

tests/test_interpolation.py

@@ -0,0 +1,102 @@
+from __future__ import (
+    unicode_literals,
+    absolute_import,
+    print_function,
+    division,
+    )
+import os
+import aaf2
+import common
+import unittest
+
+KEYFRAME_VALUE_MARGIN_OF_ERROR = .1
+
+
+class TestKeyframeInterpolation(unittest.TestCase):
+    def test_normal_bezier(self):
+        file = os.path.join(common.test_files_dir(), 'keyframes/normal_bezier.aaf')
+        # these values are transcribed by hand from media composer
+        expected_result = {
+            0: 0.0,
+            1: 147.50,
+            2: 257.19,
+            3: 343.74,
+            4: 413.91,
+            5: 471.47,
+            6: 518.72,
+            7: 557.20,
+            8: 587.92,
+            9: 611.60,
+            10: 628.70,
+            11: 639.51,
+            12: 644.18,
+            13: 642.68,
+            14: 634.87,
+            15: 620.42,
+            16: 598.80,
+            17: 569.19,
+            18: 530.32,
+            19: 480.22,
+            20: 415.59,
+            21: 330.32,
+            22: 210.33,
+            23: 0.0,
+        }
+        with aaf2.open(file) as f:
+            # Grab the Y position parameter from this AAF
+            op_group = next(f.content.compositionmobs()).slots[8].segment.components[1]
+            param_y_pos = next(
+                param for param in op_group.parameters
+                if isinstance(param, aaf2.misc.VaryingValue)
+                and param.name == "DVE_POS_Y_U"
+            )
+            self.compare_interpolated_values(param_y_pos, expected_result)
+
+    def test_handle_past_last_keyframe(self):
+        file = os.path.join(common.test_files_dir(), 'keyframes/bezier_handle_past_last_keyframe.aaf')
+        # these values are transcribed by hand from media composer
+        expected_result = {
+            0: 0.0,
+            1: 40.2,
+            2: 79.92,
+            3: 119.09,
+            4: 157.63,
+            5: 195.45,
+            6: 232.43,
+            7: 268.39,
+            8: 303.14,
+            9: 336.38,
+            10: 367.72,
+            11: 396.57,
+            12: 422.01,
+            13: 442.48,
+            14: 454.99,
+            15: 452.45,
+            16: 409.92,
+            17: 227.30,
+            18: 107.82,
+            19: 55.0,
+            20: 26.25,
+            21: 10.24,
+            22: 2.3,
+            23: 0.0,
+        }
+        with aaf2.open(file) as f:
+            # Grab the Y position parameter from this AAF
+            op_group = next(f.content.compositionmobs()).slots[8].segment.components[1]
+            param_y_pos = next(
+                param for param in op_group.parameters
+                if isinstance(param, aaf2.misc.VaryingValue)
+                and param.name == "DVE_POS_Y_U"
+            )
+            self.compare_interpolated_values(param_y_pos, expected_result)
+
+    def compare_interpolated_values(self, parameter, expected_values):
+        # Generate the interpolated values
+        for frame_num, expected_value in expected_values.items():
+            actual_value = parameter.value_at(frame_num)
+            difference = abs(actual_value - expected_value)
+            assert difference < KEYFRAME_VALUE_MARGIN_OF_ERROR, \
+                "Expected value of {:.02f} for frame {} but got {:.02f}. Difference: {:.02f}".format(
+                    expected_value, frame_num, actual_value, difference
+                )