Recently, I wrote pos-tip.el which allows users to easily show tooltip on
arbitrary buffer position (http://www.emacswiki.org/emacs/PosTip). However,
external program xwininfo must be called for calculating the absolute
coordinates in which tooltip is shown because the location of tooltip must
be specified by absolute coordinates, so this program can work only under X
window system.
Some persons say, "We can calculate absolute coordinates by using
`frame-parameter' and `window-pixel-edges'", but it's a mistake.
To calculate absolute coordinates under X window system, users must also
obtain the pixel height of menu-bar and tool-bar and the pixel width of
frame extents, because `window-pixel-edges' returns the location of window
relative to a X window corresponding to `window-id', but `frame-parameter'
returns the location of a X window corresponding to `outer-window-id' or
`parent-id'. That is, these two functions regard the different X windows as
`frame'. Unfortunately, there is no way to obtain the tool-bar height etc.
without calling external programs such as xwininfo.
I also encountered this problem when I wrote scim-bridge.el
(http://www.emacswiki.org/emacs/ScimBridge) because SCIM requires the
clients to send the absolute coordinates of cursor location.
Please implement the functions like `posn-absolute-x-y',
`posn-at-absolute-x-y', and `window-absolute-pixel-edges'.