Using win32gui.FindWindow() results in black or white screen

Dear, List Members using the FindWindow function from win32gui to find the window handle of a certain window through window name to enable video capture of certain window results in a black screen. Although trying the same code without a window handle to default it to capturing the whole screen results in a successful video capture, the same code however results in a black or white screen when trying to capture a specific window with window handle. How can I solve this?
Code:
This is the main file, main.py
import cv2 as cv
import numpy as np
import os
from time import time
from windowcapture import WindowCapture
# Change the working directory to the folder this script is in.
# Doing this because I'll be putting the files from each video in their own folder on GitHub
os.chdir(os.path.dirname(os.path.abspath(__file__)))
# initialize the WindowCapture class
wincap = WindowCapture('Albion Online Client')
loop_time = time()
while(True):
# get an updated image of the game
screenshot = wincap.get_screenshot()
cv.imshow('Computer Vision', screenshot)
# debug the loop rate
print('FPS {}'.format(1 / (time() - loop_time)))
loop_time = time()
# press 'q' with the output window focused to exit.
# waits 1 ms every loop to process key presses
if cv.waitKey(1) == ord('q'):
cv.destroyAllWindows()
break
print('Done.')
This is the class file which gets imported into main.py, windowcapture.py
import numpy as np
import win32gui, win32ui, win32con
class WindowCapture:
# properties
w = 0
h = 0
hwnd = None
cropped_x = 0
cropped_y = 0
offset_x = 0
offset_y = 0
# constructor
def __init__(self, window_name):
# find the handle for the window we want to capture
self.hwnd = win32gui.FindWindow('UnityWndClass', window_name)
if not self.hwnd:
raise Exception('Window not found: {}'.format(window_name))
# get the window size
window_rect = win32gui.GetWindowRect(self.hwnd)
self.w = window_rect[2] - window_rect[0]
self.h = window_rect[3] - window_rect[1]
# account for the window border and titlebar and cut them off
border_pixels = 8
titlebar_pixels = 30
self.w = self.w - (border_pixels * 2)
self.h = self.h - titlebar_pixels - border_pixels
self.cropped_x = border_pixels
self.cropped_y = titlebar_pixels
# set the cropped coordinates offset so we can translate screenshot
# images into actual screen positions
self.offset_x = window_rect[0] + self.cropped_x
self.offset_y = window_rect[1] + self.cropped_y
def get_screenshot(self):
# get the window image data
wDC = win32gui.GetWindowDC(self.hwnd)
dcObj = win32ui.CreateDCFromHandle(wDC)
cDC = dcObj.CreateCompatibleDC()
dataBitMap = win32ui.CreateBitmap()
dataBitMap.CreateCompatibleBitmap(dcObj, self.w, self.h)
cDC.SelectObject(dataBitMap)
cDC.BitBlt((0, 0), (self.w, self.h), dcObj, (self.cropped_x, self.cropped_y), win32con.SRCCOPY)
# convert the raw data into a format opencv can read
#dataBitMap.SaveBitmapFile(cDC, 'debug.bmp')
signedIntsArray = dataBitMap.GetBitmapBits(True)
img = np.fromstring(signedIntsArray, dtype='uint8')
img.shape = (self.h, self.w, 4)
# free resources
dcObj.DeleteDC()
cDC.DeleteDC()
win32gui.ReleaseDC(self.hwnd, wDC)
win32gui.DeleteObject(dataBitMap.GetHandle())
# drop the alpha channel, or cv.matchTemplate() will throw an error like:
# error: (-215:Assertion failed) (depth == CV_8U || depth == CV_32F) && type == _templ.type()
# && _img.dims() <= 2 in function 'cv::matchTemplate'
img = img[...,:3]
# make image C_CONTIGUOUS to avoid errors that look like:
# File ... in draw_rectangles
# TypeError: an integer is required (got type tuple)
# see the discussion here:
# https://github.com/opencv/opencv/issues/14866#issuecomment-580207109
img = np.ascontiguousarray(img)
return img
# find the name of the window you're interested in.
# once you have it, update window_capture()
# https://stackoverflow.com/questions/55547940/how-to-get-a-list-of-the-name-of-every-open-window
def list_window_names(self):
def winEnumHandler(hwnd, ctx):
if win32gui.IsWindowVisible(hwnd):
print(hex(hwnd), win32gui.GetWindowText(hwnd))
win32gui.EnumWindows(winEnumHandler, None)
# translate a pixel position on a screenshot image to a pixel position on the screen.
# pos = (x, y)
# WARNING: if you move the window being captured after execution is started, this will
# return incorrect coordinates, because the window position is only calculated in
# the __init__ constructor.
def get_screen_position(self, pos):
return (pos[0] + self.offset_x, pos[1] + self.offset_y)
This code was run on a HP Pavilion Gaming Laptop, Model: 15-dk1056wm
This laptop was running a 24 bit depth display
This code was run in a python virtual environment using virtualenv, this virtual environment was running Python 3.8.0 – 32 bit
Code dependencies:
appdirs==1.4.4
distlib==0.3.2
filelock==3.0.12
numpy==1.20.3
opencv-python==4.5.2.52
pywin32==301
six==1.16.0
virtualenv==20.4.7
Sent from<https://go.microsoft.com/fwlink/?LinkId=550986> Mail for Windows 10
Sincerely, A Fellow List Member

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