Python win32ui.error: CreateCompatibleDC failed

Question

I'm trying to capture sceen using win32 for opencv but when i start it gives me an error about the CreateCompatibleDC function.

That's the first time i touch this library so i don't really know how to fix this.

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(None, 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)

That's what i wrote, referring to Learn Code By Gaming video

But when start, here's the error:

File "C:\X\windowcapture.py", line 49, in get_screenshot
        dataBitMap.CreateCompatibleBitmap(dcObj, self.w, self.h)
    win32ui.error: CreateCompatibleDC failed

replacement: `d3dshot`, python module, findable on pypi (pip). you seem to want to capture specific windows though, and I don't think d3dshot can do that. ... ah the video mentions d3dshot already. oh well. — Christoph Rackwitz, Jun 29 '21 at 17:40
does the named window even exist? your post lacks the code that actually runs this code. — Christoph Rackwitz, Jun 29 '21 at 17:46

score 2 · Answer 1 · answered Sep 23 '21 at 05:00

From:

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

To:

border_pixels = 1  # <-- Change this
titlebar_pixels = 10  # <-- Change this
self.w = self.w - border_pixels  # <-- Change this
self.h = self.h - titlebar_pixels - border_pixels
self.cropped_x = border_pixels
self.cropped_y = titlebar_pixels

Libo · Answer 2 · 2022-06-03T08:36:22.070

0

It seems win32gui API cannot creat the bitmap for you programming.

So at very first, you must keep the window that you want capture being active (not minimized or not created) Left that window behind your code window then try again.

edited Jun 03 '22 at 08:36

answered Jun 03 '22 at 08:34

Libo

11
3

score 0 · Answer 3 · answered Jun 06 '22 at 20:48

#ya just confirming what he said is correct and works. Not sure why but it does #lower your fps minorly, unless your on a lower end machine tho not a big #issue:

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
To:

border_pixels = 1  # <-- Change this
titlebar_pixels = 10  # <-- Change this
self.w = self.w - border_pixels  # <-- Change this
self.h = self.h - titlebar_pixels - border_pixels
self.cropped_x = border_pixels
self.cropped_y = titlebar_pixels

Python win32ui.error: CreateCompatibleDC failed

3 Answers3

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