A gauge needle, of sorts!

py/hexagram/dial.py

@@ -55,6 +55,30 @@ class Dial(Gauge):
 
         cr.stroke()
 
+    def draw_needle(self, cr: cairo.Context, min_radius: float, max_radius: float, value: float):
+        angle = self.min_angle + \
+            ((self.max_angle - self.min_angle) * (value / self.max_value)) \
+            - self.ANGLE_OFFSET - 4 * (math.pi / 180.0)
+
+        angle_start = angle - 4 * (math.pi / 180.0)
+        angle_end   = angle + 4 * (math.pi / 180.0)
+
+        cr.set_source_rgba(1, 1, 1, 0.75)
+
+        cr.move_to(self.x + (min_radius * self.radius) * math.cos(angle_start),
+                   self.y + (min_radius * self.radius) * math.sin(angle_start))
+
+        cr.line_to(self.x + (max_radius * self.radius) * math.cos(angle),
+                   self.y + (max_radius * self.radius) * math.sin(angle))
+
+        cr.line_to(self.x + (max_radius * self.radius) * math.cos(angle_end),
+                   self.y + (max_radius * self.radius) * math.sin(angle_end))
+
+        cr.line_to(self.x + (min_radius * self.radius) * math.cos(angle_end),
+                   self.y + (min_radius * self.radius) * math.sin(angle_end))
+
+        cr.fill()
+
     def draw_bg(self, cr: cairo.Context):
         arc = (self.x,
                self.y,