DMXGetWindowAttributes − determine back-end window attributes
When calling DMXGetWindowAttributes(), window specifies the window ID of a window on the Xdmx(1) server and available_count specifies the length of attr.
The number of screens for which information is available will be returned in screen_count and information about those screen will be returned in attr. If screen_count is less than available_count, then information for all of the screens will be returned. Otherwise, information for the first available_count screens will be returned.
The DMXWindowAttributes structure is:
XRectangle pos, vis;
For each back-end X server that displays a portion of window, this structure contains the physical screen containing that portion, the window ID on the back-end X server of the window containing that portion, the position and dimensions of the window on the back-end (pos, in screen coordinates), and the visible area of the window on the back-end (vis, in window-relative coordinates -- all zeros if the window is not visible on the backend).
To obtain more information about the physical screen use the DMXGetScreenAttributes(3) call.
Note that DMX allows multiple back-end windows to overlap in their view of the DMX logical window. Further, a logical window does not have to be completely covered by back-end windows -- there may be gaps.
As an example, consider a 500x500 window that spans the top two 1024x768 back-end displays (A and B) of a 2048x1536 DMX display composed of 4 1024x768 back-end displays arranged in a cube:
In this case, the DMXGetWindowAttributes call would return the following information for the 500x500 window:
500x500 window at 1024-250,0 (relative to back end)
with 250x500 visible at 0,0 (relative to window origin)
500x500 window at -250,0 (relative to back end)
with 250x500 visible at 250,0 (relative to window origin)
display C: 500x500 window at 1024-250,-768 with 0x0 visible at 0,0
display D: 500x500 window at -250,-768 with 0x0 visible at 0,0
DMXGetWindowAttributes() returns True unless there is a protocol error.
DMXGetWindowAttributes() can generate BadWindow and BadAlloc errors.
Because this call transports a great deal of information over the wire, please call DMXGetScreenCount(3) first, and make sure attr is sufficiently large.
On a particular back-end server, it is possible that the associated window has not yet been mapped because the XMapWindow(3) call that will eventually map the window had been buffered by Xlib’s normal buffering system. To avoid this race condition, please call DMXSync(3) before communicating directly with the back-end X server.
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