Re: Take a screenshot from within Emacs

[Eli Zaretskii <eliz@gnu.org>]

> From: joakim@verona.se
> Date: Thu, 07 Jul 2016 21:57:41 +0200
> Cc: Emacs developers <emacs-devel@gnu.org>
> 
> I don't think Emacs has the capability to access its internal rendering
> data out of the box.

Actually, it does, sort of.  Take a look at the dump-glyph-matrix
function and the subroutines it calls.  There are also
dump-frame-glyph-matrix (for TTY frames) and dump-tool-bar-row.  They
describe the data structures Emacs uses to draw its windows and
frames.  We could use them to provide some initial testing capability
for the display engine.  The disadvantages of using these functions
are that (a) they currently need Emacs build with GLYPH_DEBUG defined,
and (b) they don't test the terminal-specific parts of the display
engine (in xterm.c, w32term.c, nsterm.m, etc.) that actually write to
the glass.