From 233a909160e6e590e6947f9dbfcaa9d0e3c57729 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Mon, 16 Mar 2020 17:05:44 +0100
Subject: [PATCH] term: ptmx: don't enqueue extra frame render when app sync
 updates have been changed

Track whether app-sync updates were enabled or disabled while handling
the current chunk of PTMX data.

This fixes and issue where we called render_refresh() unnecessarily
under (at least) the following conditions:

* Application sent "BSU <data> ESU" in the *same* chunk. In this case
  we never saw that app sync was enabled and triggered delayed
  rendering as usual.

* Application sent ESU. While we had noticed app sync updates being
  enabled in earlier PTMX reads, when it was disabled *in the current*
  PTMX read, we treated it as if it had not been enabled at all.

  This caused us to trigger delayed rendering.

  Now we call render_refresh() directly from ESU, and detect the "flip
  off" case in PTMX read and avoid triggering a delayed rendering.

The end result of all this is that each key press (for e.g. scrolling
in a pager application) went from two frames being rendered, to a
single frame.
---
 terminal.c | 14 ++++++++++++--
 terminal.h |  1 +
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/terminal.c b/terminal.c
index 552b8d2a..bd55c41a 100644
--- a/terminal.c
+++ b/terminal.c
@@ -153,6 +153,8 @@ fdm_ptmx(struct fdm *fdm, int fd, int events, void *data)
     /* Prevent blinking while typing */
     term_cursor_blink_restart(term);
 
+    term->render.app_sync_updates.flipped = false;
+
     uint8_t buf[24 * 1024];
     ssize_t count = sizeof(buf);
 
@@ -198,8 +200,11 @@ fdm_ptmx(struct fdm *fdm, int fd, int events, void *data)
      * has any effect when the renderer is idle.
      */
     if (term->window->frame_callback == NULL) {
-        if (term->render.app_sync_updates.enabled)
-            term->render.refresh.grid = true;
+        if (term->render.app_sync_updates.enabled ||
+            term->render.app_sync_updates.flipped)
+        {
+            ;
+        }
 
         else {
             /* First timeout - reset each time we receive input. */
@@ -2032,6 +2037,9 @@ term_spawn_new(const struct terminal *term)
 void
 term_enable_app_sync_updates(struct terminal *term)
 {
+    if (!term->render.app_sync_updates.enabled)
+        term->render.app_sync_updates.flipped = true;
+
     term->render.app_sync_updates.enabled = true;
 
     if (timerfd_settime(
@@ -2057,6 +2065,8 @@ term_disable_app_sync_updates(struct terminal *term)
         return;
 
     term->render.app_sync_updates.enabled = false;
+    term->render.app_sync_updates.flipped = true;
+    render_refresh(term);
 
     /* Reset timers */
     timerfd_settime(
diff --git a/terminal.h b/terminal.h
index 67785399..3685c0d7 100644
--- a/terminal.h
+++ b/terminal.h
@@ -350,6 +350,7 @@ struct terminal {
         struct {
             bool enabled;
             int timer_fd;
+            bool flipped;
         } app_sync_updates;
 
         /* Render threads + synchronization primitives */