C / C++ / MFC

16-Jan-04 10:59

Ok, I know how to use the GetPixel function, the only problem is that I must get the DC of an inactive/minimized window. I've tried HDC hdc = ::GetWindowDC(hwnd), HDC hdc = ::GetDC(hwnd), HDC hdc = ::LockWindowUpdate(hwnd), but all of them returns -1 when I call the GetPixel function on any pixel of that DC.

If I can figure this out, it would GREATLY help my project.

Thanks a lot in advance

~Mike

Jörgen Sigvardsson16-Jan-04 12:17

Jörgen Sigvardsson

16-Jan-04 12:17

You can't get pixels from a minimized window. There is no "canvas". Smile | :)

--
Seraphim Shock. Gold for your ears.

__Cerb16-Jan-04 12:22

16-Jan-04 12:22

So in no way I can do this?

Damn, that sucks. With this, my project would have been so great...

Jörgen Sigvardsson16-Jan-04 12:27

Jörgen Sigvardsson

16-Jan-04 12:27

Not to my knowledge, no. The device context mirrors what's shown on screen. If there's nothing on screen, then there are no pixels to grab.

This window you're trying to snatch pixels from.. is it in the same process as your pixel grabbing routine? If it is, you could always make the "source window" double buffered. That is, it keeps a bitmap of itself internally. That way you could access the bitmap for pixels. Otherwise it's a pretty tough job I reckon.

By the way, after GetPixel() returns -1, have you checked the error code? Either call GetLastError() or add the @err pseudo-variable in the watch window in the debugger.

--
Seraphim Shock. Gold for your ears.

__Cerb16-Jan-04 12:31

16-Jan-04 12:31

Well, I have a game window opened and minimized, I'm using ::FindWindow to get its HWND value, I tried all possible ways to get the window's DC, but couldn't.

Would it be possible to get a bitmap or a BitBlt and get the pixel I want from it? If so, how could I do it?

Thanks a lot for your help

~Mike

l a u r e n16-Jan-04 14:07

16-Jan-04 14:07

i think u can send it a wm_paint message and pass a dc in
then it draws to that dc
and u can grab what u like

"there is no spoon"
biz stuff about me

__Cerb16-Jan-04 14:29

16-Jan-04 14:29

Uh? Pass a DC in a WM_PAINT message?

How do you do that?

I doubt it's possible...

~Mike

l a u r e n16-Jan-04 14:34

16-Jan-04 14:34

sorry
brainfreeze

wm_print or wm_printclient

Wink | ;)

"there is no spoon"
biz stuff about me

__Cerb16-Jan-04 14:59

16-Jan-04 14:59

Uh this won't work. Sending a message to a window is not like retrieving a HDC, so it won't return the HDC of the window.

l a u r e n16-Jan-04 15:17

16-Jan-04 15:17

dude
u pass the hdc in as athe wparam and the app _might_ paint on it
if ur lucky
i thought that was what u wanted?

"there is no spoon"
biz stuff about me

__Cerb16-Jan-04 15:20

16-Jan-04 15:20

Whatever, any serious responses please?

Jörgen Sigvardsson17-Jan-04 8:52

Jörgen Sigvardsson

17-Jan-04 8:52

I don't think it'll work with WM_PRINT. HDCs are inprocess handles I believe (not entirely sure about that though). Sending an HDC from one process to another will at best result in nothing. I think the only way is to grab a handle to the window, and then acquire a HDC from that window handle.

--
Seraphim Shock. Gold for your ears.

l a u r e n17-Jan-04 8:59