Re: Redisplay hook

["Clément Pit--Claudel" <clement.pit@gmail.com>]

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On 2016-07-03 03:45, Eli Zaretskii wrote:
>> Cc: emacs-devel@gnu.org
>> From: Clément Pit--Claudel <clement.pit@gmail.com>
>> Date: Sun, 3 Jul 2016 00:36:07 -0400
>>
>> It's true :) I'd like to make screencasts (gifs) by saving a picture of an Emacs window or frame after each redisplay (I tried a number of programs that record screencasts, but they all gave disappointing results; by saving a picture (and a timestamp) after each redisplay, I might get much better results).
> 
> As a temporary measure, try calling your code from the function
> update_end (you will have to modify the C sources for that).

Thanks for the pointer. I applied the attached patch, and it works very nicely. Could we refine it into a proper feature and apply it to master? Or are there reasons against a post-display hook?

> I think such an application needs to hook into the GUI system, not
> into Emacs.  That's because, at least on X, AFAIK Emacs doesn't
> necessarily flush the queue of X commands each time it finishes
> redisplay, so you may be disappointed by the results anyway.

It actually works very nicely :) Out of luck, maybe? In any case, I've uploaded a screencast generated by saving a screenshot at the end of each redisplay cycle to http://web.mit.edu/cpitcla/www/emacs-screencast.gif . Let me know what you think! It behaves nicely wrt, for example, the pulsing of xref-find-definition or the animations of M-x butterfly.

Cheers,
Clément.

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From c9cfc3e17b5bddb3a19951344da8d1c947d56643 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20Pit--Claudel?= <clement.pitclaudel@live.com>
Date: Sun, 3 Jul 2016 19:58:35 -0400
Subject: [PATCH] Add a post_display_hook

---
 src/xterm.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/xterm.c b/src/xterm.c
index 9fb19a1..f8e3ef0 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -1230,8 +1230,11 @@ x_update_end (struct frame *f)
   XFlush (FRAME_X_DISPLAY (f));
   unblock_input ();
 #endif
-}
 
+  block_input ();
+  run_hook(Qpost_redisplay_hook);
+  unblock_input ();
+}
 
 /* This function is called from various places in xdisp.c
    whenever a complete update has been performed.  */
@@ -12739,6 +12742,12 @@ With MS Windows or Nextstep, the value is t.  */);
 #endif
 
   DEFSYM (Qmodifier_value, "modifier-value");
+  DEFSYM (Qpost_redisplay_hook, "post-redisplay-hook");
+
+  DEFVAR_LISP ("post-redisplay-hook", Vpost_redisplay_hook,
+    doc: /* Hook run at end of redisplay.  */);
+  Vpost_redisplay_hook = Qnil;
+
   DEFSYM (Qalt, "alt");
   Fput (Qalt, Qmodifier_value, make_number (alt_modifier));
   DEFSYM (Qhyper, "hyper");
-- 
2.9.0


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