From e760f2df6b5d0958c458898c566152ed53fc90f5 Mon Sep 17 00:00:00 2001
From: Tim Allen <screwtape@froup.com>
Date: Fri, 15 May 2020 20:47:10 +1000
Subject: [PATCH] Use iTerm2 "synchronised update" sequences around redraws.

In terminals that support it, this sequence causes the terminal to not redraw
*its* output until the application has finished, reducing redraw flickering.

The sequence is defined in:

    https://gitlab.com/gnachman/iterm2/-/wikis/synchronized-updates-spec

...and is apparently also supported by kitty and libVTE.

Fixes #3482.
---
 src/terminal_ui.cc | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/terminal_ui.cc b/src/terminal_ui.cc
index b98e2e55..6b2a5966 100644
--- a/src/terminal_ui.cc
+++ b/src/terminal_ui.cc
@@ -226,6 +226,9 @@ void TerminalUI::Screen::output(bool force)
     if (lines.empty())
         return;
 
+    // iTerm2 "begin synchronised update" sequence
+    printf("\033P=1s\033\\");
+
     struct Change { int keep; int add; int del; };
     Vector<Change> changes{Change{}};
     auto new_hashes = lines | transform([](auto& line) { return hash_value(line.atoms); }) | gather<Vector>();
@@ -293,6 +296,9 @@ void TerminalUI::Screen::output(bool force)
             }
         }
     }
+
+    // iTerm2 "endsynchronised update" sequence
+    printf("\033P=2s\033\\");
 }
 
 constexpr int TerminalUI::default_shift_function_key;