Fixed ellipse after writing some tests to identify the problem

chris_ellipse_exploration/ellipse.py

@@ -17,6 +17,7 @@ def ellipse(rx, ry, num_points, points_to_draw=None):
     for i in range(points_to_draw or num_points):
         φi = get_angle(rx, ry, num_points, i)
         di = get_distance(rx, ry, num_points, i)
+        print(i, φi, di)
         left(φi)
         forward(di)
     left(-π/2)
@@ -79,9 +80,10 @@ def project_onto_basis(vec, basis):
     is perpendicular (vec_b). 
     """
     v0, v1 = vec
-    b0, b1 = basis
-    len_a = dot(vec, basis)
-    vec_a = (len_a * v0, len_a * v1)
+    unit_basis = normalize(basis)
+    b0, b1 = unit_basis
+    len_a = dot(vec, unit_basis)
+    vec_a = (len_a * b0, len_a * b1)
     vec_b = get_vector(vec_a, vec)
     return vec_a, vec_b
 
@@ -93,6 +95,13 @@ def dot(vec0, vec1):
     x1, y1 = vec1
     return x0 * x1 + y0 * y1
 
+def normalize(vec):
+    """Scales vec to magnitude 1.
+    """
+    x, y = vec
+    len_vec = mag(vec)
+    return x / len_vec, y / len_vec
+
 def mag(vec):
     """Returns the magnitude, or length, of a vector.
     We can simplify the familiar formula sqrt(x*x + y*y)

chris_ellipse_exploration/ellipse_test.py

@@ -1,5 +0,0 @@
-from ellipse import ellipse
-
-ellipse(100, 200, 1024)
-
-input()

chris_ellipse_exploration/tests.py

@@ -0,0 +1,24 @@
+# To run these tests run: python -m unittest tests
+
+from unittest import TestCase
+from ellipse import *
+from math import sqrt
+
+class TestEllipseFunctions(TestCase):
+    def test_normalize(self):
+        observed = normalize((0, 1))
+        expected = (0, 1)
+        self.assertEqual(observed, expected)
+
+        observed = normalize((2, 0))
+        expected = (1, 0)
+        self.assertEqual(observed, expected)
+
+        observed = normalize((1, 1))
+        expected = (1/sqrt(2), 1/sqrt(2))
+        self.assertEqual(observed, expected)
+
+    def test_project_onto_basis(self):
+        observed = project_onto_basis((4, 3), (4, 0))
+        expected = ((4, 0), (0, 3))
+        self.assertEqual(observed, expected)