added a pointer to the knob

knob.py

@@ -1,4 +1,5 @@
 import pygame
+import math
 
 class Knob:
     
@@ -7,7 +8,17 @@ class Knob:
         self.radius = screen.get_width()/20
         self.fill_color = (255,0,255)
         self.position = (screen.get_width()/2, screen.get_height()/2)
+        self.value = 0.1
+
+    def set_value(self, value):
+        self.value = value
+
+    def get_pointer_position(self):
+        x = self.radius * math.cos((self.value * 2 + 0.5) * math.pi) + self.position[0]
+        y = self.radius * math.sin((self.value * 2 + 0.5) * math.pi) + self.position[1]
+        return(x, y)
 
     def display(self):
-        pygame.draw.circle(self.screen, self.fill_color , self.position, self.radius)
+        pygame.draw.circle(self.screen, self.fill_color, self.position, self.radius)
+        pygame.draw.line(self.screen, "black", self.position, self.get_pointer_position(), 3)