From 02ee570c272e93b29621a4dfc2f546c1b8e1bb2b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Tue, 10 Nov 2020 19:20:35 +0100
Subject: [PATCH] =?UTF-8?q?wayland:=20preempt=20render=20scheduling=20in?=
 =?UTF-8?q?=20=E2=80=98configure=E2=80=99=20events?=
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A configure event must be “committed”. In case of resizing, that means
rendering a new frame and committing that surface.

render_resize() will resize the grid and *schedule* a render
refresh. However, if one is already pending, the refresh will take a
very (relatively) long time - until the next frame callback is
received.

This poses a problem when the window is hidden, since in this case,
the frame callback *never* comes. This in turn means we fail to commit
a new surface in response to the ‘configure’ event. And that means the
compositor needs to wait for a transaction timeout before continuing.

The end effect is very slow and jerky window resizing when a hidden
foot window is being resized.

This can happen in tiled compositors, like Sway, where a window can be
tabbed (and thus invisible), but still resized when its container is
resized.

Closes #190
---
 CHANGELOG.md |  2 ++
 wayland.c    | 19 ++++++++++++++-----
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 645b6eeb..468f897d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -68,6 +68,8 @@
   not possible to add a command to these actions when used in mouse
   bindings, making them useless
   (https://codeberg.org/dnkl/foot/issues/183).
+* Resize very slow when window is hidden
+  (https://codeberg.org/dnkl/foot/issues/190).
 
 
 ### Security
diff --git a/wayland.c b/wayland.c
index 37b47f30..b8cd9cd9 100644
--- a/wayland.c
+++ b/wayland.c
@@ -614,17 +614,26 @@ xdg_surface_configure(void *data, struct xdg_surface *xdg_surface,
 
     xdg_surface_ack_configure(xdg_surface, serial);
 
-    /* TODO: check with GNOME and tiling - presumably that didn't work
-     * unless we presented a *new* buffer, hence we used to do a force
-     * resize here */
-    bool resized = render_resize(term, win->configure.width, win->configure.height);
+    if (term->window->frame_callback != NULL) {
+        /*
+         * Preempt render scheduling.
+         *
+         * Each configure event require a corresponding new
+         * surface+commit. Thus we cannot just schedule a pending
+         * refresh if there’s already a frame being rendered.
+         */
+        wl_callback_destroy(term->window->frame_callback);
+        term->window->frame_callback = NULL;
+    }
+
+    bool resized = render_resize(
+        term, win->configure.width, win->configure.height);
 
     if (win->configure.is_activated)
         term_visual_focus_in(term);
     else
         term_visual_focus_out(term);
 
-    /* TODO: remove - shouldn't be necessary with render_resize_force() */
     if (!resized) {
         /*
          * If we didn't resize, we won't be committing a new surface