Get drop shadow dimensions of window

Question

I need to know the drop shadow dimensions of a window. I tried receiving values via the GetSystemMetrics WinAPI function, but I could not find the parameter to pass over. Any idea on how I can get this value globally (or for a single window handle)? I know that the width of a drop shadow depends on the window type (dialog/normal/and so on). Ibwould implement this functionality using C#, but C++ would also be fine.

Answer 1

There is a way using the DWM API to figure out the size of the drop shadow, however, it does not work until the window is visible.

In previous versions of Windows, there was the Client Rect, and the Window Rect. But ever since Vista came out, there has been a third Rect for a window called the Extended Frame Bounds. The third rect is larger than the Client Rect and smaller than the Window Rect, and excludes the area taken up by the drop shadow.

Call DwmGetWindowAttribute(hwnd, DWMWA_EXTENDED_FRAME_BOUNDS, &rect, sizeof(RECT)) to read the Extended Frame Bounds rect. This function is from <dwmapi.h>, and is not available in Windows XP or earlier.

Note that if you call this before the window has been shown, you will get incorrect results.

EDIT:

Note that Extended Frame Bounds are in physical pixel coordinates, and are not affected by the Scaling features of Windows. You may need to convert back to virtual coordinates, or convert the virtual coordinates to physical coordinates to make them match.

Answer 2

As far as I know there is no way of obtaining that information. Programs such as WindowClippings solve it by taking a screenshot and cropping to the shadow dimensions afterwards.