Win32 HighGUI backend can't turn top-most state off #25833
Description
Verified on Win10 21H2 with OpenCV 4.8.0 (standard build). However, the code remains the same since this was introduced by #14872 (Looks like in milestone 3.4.8, so that corresponds with 4.1.2?) it's going to affect quite a few releases.
The issue can be reproduced using the following Python script:
import cv2
import numpy as np
frame = np.zeros((240, 320, 3), np.uint8)
window = "Test Window"
def show_window(window, frame):
print(cv2.getWindowProperty(window, cv2.WND_PROP_TOPMOST))
while(True):
cv2.imshow(window, frame)
if cv2.waitKey() > 0:
break
cv2.namedWindow(window)
cv2.setWindowProperty(window, cv2.WND_PROP_TOPMOST, 1)
show_window(window, frame)
cv2.setWindowProperty(window, cv2.WND_PROP_TOPMOST, 0)
show_window(window, frame)
It prints
1.0
1.0
and the window remains top-most.
I've gone into details in this StackOverflow answer, and concluded that the problem is in the following line:
opencv/modules/highgui/src/window_w32.cpp
Line 684 in be00247
Based on how I interpret the documentation of SetWindowPos, HWND_TOP is not the right way, it should be HWND_NOTOPMOST.
This can be verified by the following hack:
import cv2
import numpy as np
import win32gui
import win32con
frame = np.zeros((240, 320, 3), np.uint8)
window = "Test Window"
def show_window(window, frame):
print(cv2.getWindowProperty(window, cv2.WND_PROP_TOPMOST))
while(True):
cv2.imshow(window, frame)
if cv2.waitKey() > 0:
break
cv2.namedWindow(window)
cv2.setWindowProperty(window, cv2.WND_PROP_TOPMOST, 1)
show_window(window, frame)
wnd_handle = win32gui.FindWindow(None, window)
win32gui.SetWindowPos(wnd_handle, win32con.HWND_NOTOPMOST, 0, 0, 0, 0, win32con.SWP_NOMOVE + win32con.SWP_NOSIZE);
show_window(window, frame)
The actual fix is trivial, add the missing "NO" and "MOST".