Arrow normal direction bug fix

bell.py

@@ -126,13 +126,10 @@ class DirectionOfPolarization(FilterScene):
         )
 
     def continual_update(self):
+        reference_angle = self.reference_line.get_angle()
+        self.em_wave.rotation = reference_angle
         FilterScene.continual_update(self)
-        wave = self.em_wave.mobject
-        angle = self.reference_line.get_angle()
-        wave.rotate(
-            angle, self.em_wave.propogation_direction,
-            about_point = self.em_wave.start_point,
-        )
+        vect_groups = [self.em_wave.E_vects, self.em_wave.M_vects]
         if self.apply_filter:
             filters = sorted(
                 self.pol_filters,
@@ -143,7 +140,7 @@ class DirectionOfPolarization(FilterScene):
             )
             for pol_filter in filters:
                 filter_x = pol_filter.get_center()[0]
-                for vect_group, angle in (self.em_wave.E_vects, 0), (self.em_wave.M_vects, -np.pi/2):
+                for vect_group, angle in zip(vect_groups, [0, -np.pi/2]):
                     proj_vect = rotate_vector(
                         OUT, pol_filter.filter_angle + angle, RIGHT,
                     )
@@ -156,6 +153,8 @@ class DirectionOfPolarization(FilterScene):
                         if start[0] > filter_x:
                             vect.apply_matrix(proj_matrix)
                             vect.shift(start - vect.get_start())
+                            vect.set_tip_points(vect.tip)
+                            vect.set_rectangular_stem_points()
 
 class PhotonPassesCompletelyOrNotAtAll(DirectionOfPolarization):
     CONFIG = {
@@ -410,11 +409,11 @@ class SecondVideoWrapper(Scene):
 class BasicsOfPolarization(DirectionOfPolarization):
     def construct(self):
         self.show_continual_wave()
-        self.show_photons()
+        # self.show_photons()
 
     def show_continual_wave(self):
         em_wave = self.em_wave
-        em_wave.M_vects.set_fill(opacity = 0.5)
+        # em_wave.M_vects.set_fill(opacity = 0.25)
 
         title = TextMobject("Waves in the ``electromagnetic field''")
         title.to_edge(UP)
@@ -1088,5 +1087,6 @@ class VennDiagramProofByContradiction(Scene):
 
 
 
+
 
 

topics/geometry.py

@@ -231,7 +231,8 @@ class Arrow(Line):
         tbp1, tbp2 = tip_base_points
         perp_vect = tbp2 - tbp1
         tip_base_width = np.linalg.norm(perp_vect)
-        perp_vect /= tip_base_width
+        if tip_base_width > 0:
+            perp_vect /= tip_base_width
         width = min(
             self.rectangular_stem_width,
             self.max_stem_width_to_tip_width_ratio*tip_base_width,
@@ -283,8 +284,8 @@ class Arrow(Line):
         return self
 
     def get_normal_vector(self):
-        p1, p2, p3 = self.tip.get_anchors()
-        result = np.cross(p2 - p1, p3 - p2)
+        p0, p1, p2 = self.tip.get_anchors()
+        result = np.cross(p2 - p1, p1 - p0)
         norm = np.linalg.norm(result)
         if norm == 0:
             return self.normal_vector
@@ -306,7 +307,7 @@ class Arrow(Line):
 
     def put_start_and_end_on(self, *args, **kwargs):
         Line.put_start_and_end_on(self, *args, **kwargs)
-        self.set_tip_points(self.tip)
+        self.set_tip_points(self.tip, preserve_normal = False)
         self.set_rectangular_stem_points()
 
     def scale(self, scale_factor, **kwargs):

waves.py

@@ -117,10 +117,13 @@ class EMWave(ContinualAnimationGroup):
     }
     def __init__(self, **kwargs):
         digest_config(self, kwargs)
-        self.matrix_transform = np.dot(
-            z_to_vector(self.propogation_direction),
-            np.linalg.inv(z_to_vector(RIGHT)),
-        )
+        if not all(self.propogation_direction == RIGHT):
+            self.matrix_transform = np.dot(
+                z_to_vector(self.propogation_direction),
+                np.linalg.inv(z_to_vector(RIGHT)),
+            )
+        else:
+            self.matrix_transform = None
 
         vector_oscillations = []
         self.E_vects = VGroup()
@@ -161,7 +164,8 @@ class EMWave(ContinualAnimationGroup):
     def update_mobject(self, dt):
         ContinualAnimationGroup.update_mobject(self, dt)
         self.mobject.rotate(self.rotation, RIGHT)
-        self.mobject.apply_matrix(self.matrix_transform)
+        if self.matrix_transform:
+            self.mobject.apply_matrix(self.matrix_transform)
         self.mobject.shift(self.start_point)
 
 class WavePacket(Animation):