utils.py

import time
import cv2

# An FPS tracker that computes exponentialy moving average FPS
class FPSTracker:

    def __init__(self, ratio=0.5):
        self._last_tick = None
        self._avg_fps = None
        self.ratio = ratio

    def tick(self):
        if self._last_tick is None:
            self._last_tick = time.time()
            return None
        t_new = time.time()
        fps_sample = 1.0 / (t_new - self._last_tick)
        self._avg_fps = self.ratio * fps_sample + (1 - self.ratio) * self._avg_fps if self._avg_fps is not None else fps_sample
        self._last_tick = t_new
        return self.get()

    def get(self):
        return self._avg_fps

# Wrapper for playing a stream with cv2.imshow(). It can accept an image and return keypress info for basic interactivity.
# It also tracks FPS and optionally overlays info onto the stream.
class Displayer:

    def __init__(self, title, width=None, height=None, show_info=True):
        self.title, self.width, self.height = title, width, height
        self.show_info = show_info
        self.fps_tracker = FPSTracker()
        cv2.namedWindow(self.title, cv2.WINDOW_NORMAL)
        if width is not None and height is not None:
            cv2.resizeWindow(self.title, width, height)
    # Update the currently showing frame and return key press char code

    def step(self, image):
        if self.show_info:
            fps_estimate = self.fps_tracker.tick()
            if fps_estimate is not None:
                message = f"{int(fps_estimate)} fps | {self.width}x{self.height}"
                cv2.putText(image, message, (10, 40), cv2.FONT_HERSHEY_SIMPLEX, 1.0, (0, 0, 0))
        cv2.imshow(self.title, image)
        return cv2.waitKey(1) & 0xFF