How to get only the visible part of a window (Windows, gdi32, user32, etc)

Question

I want to get only the visible part of the window in windows, as a region.

Want to get only the area that is seen by the user. Programmatically, of course. Here is an example. I have the following window composition:

+------------------------------------------+
 |                                          |
 |           +=============+                |
 |           |             |                |
 |           |    A   +--------------------------+
 |           |        |                          |
 |    C      |        |             B            |
 |           |        +--------------------------+
 |           |             |                |
 +-----------|             |----------------+
             |             |
             +-------------+

Let's say that I am interested only in window A. Then what I would need is a handle to a region which would look like this:

          +=============+                
          |             |                
          |    A  +-----+
          |       |                          
          |       |                         
          |       +-----+
          |             |                
          |             |
          |             |
          +-------------+

Alternatively, I should be able to obtain the region of any other window in the following manner.

So far, I used this guide: http://blogs.msdn.com/b/oldnewthing/archive/2003/09/02/54758.aspx

And I agree that GetClipBox returns 0, 1, 2 or 3 if you have, accordingly, 0 -> Error, 1 for NULLREGION(the resulting rgn is invisible to the user), 2 -> SIMPLEREGION, and 3 for COMPLEXREGION. So, far, I need the complex region.

Master Question: But how do I get its coordinates and dimensions ?

(Added Info)

Is it possible to reconstruct a COMPLEXREGION (That was created by the OS, not me) to simple REGIONS of which it is composed. Feng Yuan suggests you can't:

http://www.codeguru.com/forum/archive/index.php/t-126543.html

(Added Info)

So, is there a way to find the region of A and translate it to a PolyPath or a nice geometric figure having the coordinates of its corners ?

I use JNA (Java) , by the way, but a C# or .VB code solving the same problem would be sufficient.

Cheers.

Answer 1

You can enumerate all desktop windows, plus all monitors, and combine their rectangles. I'm not sure if there is a better way.

Note that Windows "lies" about the exact dimensions of windows these days (the Aero window border is slightly bigger than actually reported unless you set a special flag).

Also note that windows can have see-through portions defined by each application (in addition to the see-through window borders you always have under Aero).

You also need to be careful on high-DPI systems where Windows "lies" to your app about coordinates unless you go out of your way to flag it as DPI-aware.

And also note that even an "invisible" window can be visible via the Taskbar, Alt-Tab or Flip3D thumbnails feature of Aero... So, really, on Vista and Windows 7 with DWM enabled, the answer is that your window is potentially always completely visible. :)