grabWindow with hwnd return black screen

Question

Why does grabwindow return black screen? Is a valid window and I do not receive any errors.

pix = QPixmap.grabWindow(hwnd)

And that way it works perfectly!

pix = QPixmap.grabWindow(QApplication.desktop().winId())

Below the complete source code:

def __init__(self):
    serverProtocol.RDCServerProtocol.__init__(self)
    self._array = QByteArray()
    self._buffer = QBuffer(self._array)
    self._buffer.open(QIODevice.WriteOnly)

def _makeFramebuffer(self, width, height):
    pix = QPixmap.grabWindow(197526) # Google Chrome Window
    pix = pix.scaled(width, height)
    if width >= self._maxWidth or height >= self._maxHeight:
        width = self._maxWidth
        height = self._maxHeight
    pix.save(self._buffer, 'jpeg')
    pixData = self._buffer.data()
    self._array.clear()
    self._buffer.close()
    return "%s" % pixData

I need to capture only the google window, but a black screen appears =/

Thank!

@rodrigosillos How do you get the hwnd (197526)?, what is your OS? — eyllanesc, May 23 '18 at 03:29
Is your chrome window maximised and visible at the time your code calls `grabWindow`? — three_pineapples, May 23 '18 at 04:17
@three_pineapples But I can close the window of the chrome even not visible — rodrigosillos, May 23 '18 at 04:29
@three_pineapples Can not capture the window if it is not visible? — rodrigosillos, May 23 '18 at 04:31
@eyllanesc https://stackoverflow.com/questions/14653168/get-hwnd-of-each-window — rodrigosillos, May 23 '18 at 04:43
No, I don't think you can grab it for minimised windows (at least using that method). The [C++ Qt Docs](http://doc.qt.io/archives/qt-4.8/qpixmap.html#grabWindow) say "The grabWindow() function grabs pixels from the screen, not from the window, i.e. if there is another window partially or entirely over the one you grab, you get pixels from the overlying window, too. The mouse cursor is generally not grabbed." By extension I assume that means minimised windows will return nothing. — three_pineapples, May 23 '18 at 06:27
@three_pineapples So I need to change the method. Instead of grab up the pixels, I grab the window screen. Right? — rodrigosillos, May 23 '18 at 13:16
@three_pineapples Even with the google chrome window visible I can not grab the pixels, a black screen is displayed =( — rodrigosillos, May 23 '18 at 13:33
@three_pineapples I can not find a method to replace grabWindow. A method that, instead of grab the screen, grab only the pixels of a specific window. — rodrigosillos, May 24 '18 at 17:55
I doubt one exists. You're basically asking to inject yourself into the painting event of another program and to read the buffer into which the painting occurs. I doubt there is a general way of doing that for a program. — three_pineapples, May 24 '18 at 22:26
@three_pineapples Understood! In fact I wanted to lock the server screen and continue to operate in the background. it is possible? Thank! — rodrigosillos, May 24 '18 at 22:32
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/171731/discussion-between-rodrigosillos-and-three-pineapples). — rodrigosillos, May 25 '18 at 00:29

grabWindow with hwnd return black screen

0 Answers0