combined with the proposed zero-delay pollKey alternative to waitKey (separate pull request), disabling VSYNC can drastically speed up display of images. I can get close to 1000 fps for a trivial example (see below), whereas with VSYNC it's nailed to 60 fps (for my screen) and with mandatory Sleep() in waitKey it's throttled to a jittery 100 FPS depending on OS scheduler.

I hope I based this on the right branch. it's not a bug fix. I think I managed to retarget this to the master branch.

I took the implementation of the TOPMOST property as a template and tried to emulate the code structure.

please let me know if I can improve or if this isn't the right way to get such code introduced.

#!/usr/bin/env python3
import time
import numpy as np
import cv2 as cv

cv.namedWindow("window", cv.WINDOW_OPENGL)
print("VSYNC is", cv.getWindowProperty("window", cv.WND_PROP_VSYNC))
cv.setWindowProperty("window", cv.WND_PROP_VSYNC, 0)
print("VSYNC is", cv.getWindowProperty("window", cv.WND_PROP_VSYNC))

i = np.eye(60, dtype=np.uint8) * 255 # cheap barber pole
cnt = 0
t0 = t1 = time.perf_counter()
while True:
	t1 = time.perf_counter()
	if t1 - t0 >= 1.0:
		t0 = t1
		print(cnt, "fps")
		cnt = 0
	i = np.roll(i, shift=1, axis=1) # roll by one column
	cv.imshow("window", i)
	cnt += 1
	key = cv.waitKey(1)
	if key in (13, 27): break

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or other license that is incompatible with OpenCV
• The PR is proposed to proper branch
• There is reference to original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

force_builders=Win32,Custom
buildworker:Custom=linux-1,linux-4,linux-6
build_image:Custom=qt:16.04