winapi - Capturing screenshots with win32api python returns black image

Question

I've used the following code examples to capture a screenshot:

https://stackoverflow.com/a/3260811 https://stackoverflow.com/a/24352388/5858697

When taking a screenshot of Firefox or chrome, they return a blank black image. Capturing a screenshot of notepad works fine. I've done some research on this and I think it's because they're gpu accelerated. Other screenshot libraries work but I need to have it so I can capture a screenshot of an application even if it's not currently visible.

Has anyone solved a similar problem or could someone point me in the right direction? Thank you.

Answer 1

Based on the @Barmak's previous answer, I converted C + + code to python, and now it works.

import win32gui
import win32ui
import win32con
from ctypes import windll
from PIL import Image
import time
import ctypes

hwnd_target = 0x00480362 #Chrome handle be used for test 

left, top, right, bot = win32gui.GetWindowRect(hwnd_target)
w = right - left
h = bot - top

win32gui.SetForegroundWindow(hwnd_target)
time.sleep(1.0)

hdesktop = win32gui.GetDesktopWindow()
hwndDC = win32gui.GetWindowDC(hdesktop)
mfcDC  = win32ui.CreateDCFromHandle(hwndDC)
saveDC = mfcDC.CreateCompatibleDC()

saveBitMap = win32ui.CreateBitmap()
saveBitMap.CreateCompatibleBitmap(mfcDC, w, h)

saveDC.SelectObject(saveBitMap)

result = saveDC.BitBlt((0, 0), (w, h), mfcDC, (left, top), win32con.SRCCOPY)

bmpinfo = saveBitMap.GetInfo()
bmpstr = saveBitMap.GetBitmapBits(True)

im = Image.frombuffer(
    'RGB',
    (bmpinfo['bmWidth'], bmpinfo['bmHeight']),
    bmpstr, 'raw', 'BGRX', 0, 1)

win32gui.DeleteObject(saveBitMap.GetHandle())
saveDC.DeleteDC()
mfcDC.DeleteDC()
win32gui.ReleaseDC(hdesktop, hwndDC)

if result == None:
    #PrintWindow Succeeded
    im.save("test.png")

Please note: Firefox uses Windowless Controls.

If you want to get the handle of Firefox, you may need UI Automation.

For a detailed explanation, please refer to @IInspectable's answer.