Beginning of eoc8

topics/objects.py

@@ -1,17 +1,82 @@
 from helpers import *
 
 from mobject import Mobject
-from mobject.vectorized_mobject import VGroup
+from mobject.vectorized_mobject import VGroup, VMobject
 from mobject.svg_mobject import SVGMobject
-from mobject.tex_mobject import TextMobject
+from mobject.tex_mobject import TextMobject, TexMobject
 
 from animation import Animation
 from animation.simple_animations import Rotating
 
-from topics.geometry import Circle, Line, Rectangle, Square
+from topics.geometry import Circle, Line, Rectangle, Square, Arc, Polygon
 from topics.three_dimensions import Cube
 
 
+class Speedometer(VMobject):
+    CONFIG = {
+        "arc_angle" : 4*np.pi/3,
+        "num_ticks" : 8,
+        "tick_length" : 0.2,
+        "needle_width" : 0.1,
+        "needle_height" : 0.8,
+        "needle_color" : YELLOW,
+    }
+    def generate_points(self):
+        start_angle = np.pi/2 + self.arc_angle/2
+        end_angle = np.pi/2 - self.arc_angle/2
+        self.add(Arc(
+            start_angle = start_angle,
+            angle = -self.arc_angle
+        ))
+        tick_angle_range = np.linspace(start_angle, end_angle, self.num_ticks)
+        for index, angle in enumerate(tick_angle_range):
+            vect = rotate_vector(RIGHT, angle)
+            tick = Line((1-self.tick_length)*vect, vect)
+            label = TexMobject(str(10*index))
+            label.scale_to_fit_height(self.tick_length)
+            label.shift((1+self.tick_length)*vect)
+            self.add(tick, label)
+
+        needle = Polygon(
+            LEFT, UP, RIGHT,
+            stroke_width = 0,
+            fill_opacity = 1,
+            fill_color = self.needle_color
+        )
+        needle.stretch_to_fit_width(self.needle_width)
+        needle.stretch_to_fit_height(self.needle_height)
+        needle.rotate(start_angle - np.pi/2)
+        self.add(needle)
+        self.needle = needle
+
+        self.center_offset = self.get_center()
+
+    def get_center(self):
+        result = VMobject.get_center(self)
+        if hasattr(self, "center_offset"):
+            result -= self.center_offset
+        return result
+
+    def get_needle_tip(self):
+        return self.needle.get_anchors()[1]
+
+    def get_needle_angle(self):
+        return angle_of_vector(
+            self.get_needle_tip() - self.get_center()
+        )
+
+    def rotate_needle(self, angle):
+        self.needle.rotate(angle, about_point = self.get_center())
+        return self
+
+    def move_needle_to_velocity(self, velocity):
+        max_velocity = 10*(self.num_ticks-1)
+        proportion = float(velocity) / max_velocity
+        start_angle = np.pi/2 + self.arc_angle/2
+        target_angle = start_angle - self.arc_angle * proportion
+        self.rotate_needle(target_angle - self.get_needle_angle())
+        return self
+
 class PartyHat(SVGMobject):
     CONFIG = {
         "file_name" : "party_hat",