ui(raylib): constant spinner rotation speed

Previously, the spinner rotation would start slow and ramp up as the
reported FPS increased. With this change the spinner speed remains
constant, and the implementation is simpler.

system/ui/spinner.py

@@ -9,7 +9,7 @@ from openpilot.system.ui.lib.application import gui_app
 # Constants
 PROGRESS_BAR_WIDTH = 1000
 PROGRESS_BAR_HEIGHT = 20
-ROTATION_TIME_SECONDS = 1.0  # Time for one full circle
+DEGREES_PER_SECOND = 360.0  # one full rotation per second
 MARGIN = 200
 TEXTURE_SIZE = 360
 FONT_SIZE = 80
@@ -43,10 +43,8 @@ class Spinner:
     spinner_origin = rl.Vector2(TEXTURE_SIZE / 2.0, TEXTURE_SIZE / 2.0)
     comma_position = rl.Vector2(center.x - TEXTURE_SIZE / 2.0, center.y - TEXTURE_SIZE / 2.0)
 
-    fps = rl.get_fps()
-    if fps > 0:
-      degrees_per_frame = 360.0 / (ROTATION_TIME_SECONDS * fps)
-      self._rotation = (self._rotation + degrees_per_frame) % 360.0
+    delta_time = rl.get_frame_time()
+    self._rotation = (self._rotation + DEGREES_PER_SECOND * delta_time) % 360.0
 
     # Draw rotating spinner and static comma logo
     rl.draw_texture_pro(self._spinner_texture, rl.Rectangle(0, 0, TEXTURE_SIZE, TEXTURE_SIZE),