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I've been looking into using the wx python package on Windows 7. Specifically, I would like to be able to get the image data of a existing window (i.e. not a window opened by the python program). It appears I can do this by getting the window's device context, creating a compatible device context, copying the bitmap, and then using it how I like from there. The problem is that I can't seem to find the way to get the device context (or the handle) of an existing window. I only see ways to get them from windows the python program using wx created. How might I be able to go about doing this? Thank you much!

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2 Answers

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wx may not have a way to do this.

The Windows APIs you need are pretty simple, and you can use them through win32api (or ctypes if you prefer, but that's a lot more work).

First, I don't know how you're planning to identify the window you want. If you have its class and name, you can just FindWindow (or, if it may not be a top-level window, FindWindowEx). If you want to search by something else, you will probably need to call EnumWindow (plus EnumChildWindows recursively, if you're not sure it's a top-level window).

At this point, you can just call wx.Windows.AssociateHandle to attach a wx.Window object to the HWND.

If you can't do that for whatever reason, GetDC gives you a display context for an HWND. You can then create a memory DC, or get the DC for the native window under underlying your wx window, and BitBlt from one to the other.

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AssociateHandle can indeed be used to work with windows created outside of the Python application. –  FogleBird Nov 15 at 1:05
 
@FogleBird: Thanks! Let me edit the answer, because that makes things simpler. –  abarnert Nov 15 at 1:06
 
Ok. I was thinking this might be the case. I was trying to do what you're suggesting, but was running into problems as I am looking for in this question. However, I wasn't getting the solution there and I've been having trouble hunting that down on my own. That was when I found wx and thought it might be a solution. –  golmschenk Nov 15 at 1:07
 
Oh! Maybe the update of using AssociateHandle will work for me. Thanks! –  golmschenk Nov 15 at 1:09
 
Check my code in my answer for that. –  FogleBird Nov 15 at 1:10
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up vote 1 down vote

Just to expand on the other answer, try this code (untested, I'm not on Windows right now)...

# first use FindWindow or FindWindowEx to determine window handle
frame = wx.Frame(None)
frame.AssociateHandle(handle)
dc = wx.ClientDC(frame)
width, height = dc.GetSize()
bitmap = wx.EmptyBitmap(width, height)
mdc = wx.MemoryDC(bitmap)
mdc.Blit(0, 0, width, height, dc, 0, 0)
del mdc
bitmap.SaveFile('output.png', wx.BITMAP_TYPE_PNG)
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Also, check out my code here which draws snowflakes on the desktop - you can also see how to use ctypes to use the FindWindow function. github.com/fogleman/wxSnow/blob/master/wxsnow.py –  FogleBird Nov 15 at 1:17
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