Give `window-text-pixel-size' optional BUFFER argument.

[This reinstalls commit 1d1162479caf1fdf48564f1486fa84e3cdacaa9b,
which I mistakenly reverted.  --eggert]
* xdisp.c (Fwindow_text_pixel_size): Add optional argument BUFFER.
* display.texi (Size of Displayed Text): Describe optional
argument BUFFER of `window-text-pixel-size'.

2 files changed, 13 insertions, 1 deletions

diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index 2cde2fb6f48..aa4d3200830 100644
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -1,3 +1,8 @@
+2015-02-01  Martin Rudalics  <rudalics@gmx.at>
+
+        * display.texi (Size of Displayed Text): Describe optional
+        argument BUFFER of `window-text-pixel-size'.
+
 2015-01-28  Eli Zaretskii  <eliz@gnu.org>
 
         * searching.texi (Regexp Search): Add a cross-reference to "Syntax
diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index b09b82a6724..10b17a3f389 100644
--- a/doc/lispref/display.texi
+++ b/doc/lispref/display.texi
@@ -1880,7 +1880,7 @@ displayed in a given window.  This function is used by
 @code{fit-frame-to-buffer} (@pxref{Size and Position}) to make a window
 exactly as large as the text it contains.
 
-@defun window-text-pixel-size &optional window from to x-limit y-limit mode-and-header-line
+@defun window-text-pixel-size &optional window from to x-limit y-limit mode-and-header-line buffer
 This function returns the size of the text of @var{window}'s buffer in
 pixels.  @var{window} must be a live window and defaults to the selected
 one.  The return value is a cons of the maximum pixel-width of any text
@@ -1919,6 +1919,13 @@ means to not include the height of the mode- or header-line of
 @code{mode-line} or @code{header-line}, include only the height of that
 line, if present, in the return value.  If it is @code{t}, include the
 height of both, if present, in the return value.
+
+The optional argument @var{buffer} allows to specify an alternate buffer
+whose text size will be calculated.  If @var{buffer} is @code{nil} or
+omitted, then operate on the buffer of @var{window}.  If it is @code{t},
+then operate on the current buffer as if it were displayed in
+@var{window}.  If it specifies a live buffer, then operate on that
+buffer as if it were displayed in @var{window}.
 @end defun