From b3a1017a264cfea7e9ae1a374208e9b02efbda5a Mon Sep 17 00:00:00 2001
From: Maxime Coste <mawww@kakoune.org>
Date: Thu, 9 Sep 2021 08:59:26 +1000
Subject: [PATCH] Remove scrolling detection/optimization in terminal output

Just validate if line changed or not. This should avoid flickering
on terminals such as the linux console that eagerly redraw on line
deletions. Unfortunately this means drawing will use more data and
might add a bit of latency on slow links.

Fixes #4317
Fixes #4320
---
 src/terminal_ui.cc | 88 ++++++++++++++--------------------------------
 1 file changed, 26 insertions(+), 62 deletions(-)

diff --git a/src/terminal_ui.cc b/src/terminal_ui.cc
index 67b21e7f..e9519cce 100644
--- a/src/terminal_ui.cc
+++ b/src/terminal_ui.cc
@@ -286,7 +286,7 @@ void TerminalUI::Screen::output(bool force, bool synchronized, Writer& writer)
 
     // iTerm2 "begin synchronized update" sequence
     if (synchronized)
-        writer.write("\033P=1s\033\\");
+        writer.write("\033[?2026h");
 
     if (force)
     {
@@ -299,77 +299,41 @@ void TerminalUI::Screen::output(bool force, bool synchronized, Writer& writer)
         return (hash_value(line.atoms) << 1) | 1; // ensure non-zero
     };
 
-    struct Change { int keep; int add; int del; };
-    Vector<Change> changes{Change{}};
-    auto new_hashes = ArrayView{lines.get(), (size_t)size.line} | transform(hash_line);
-    for_each_diff(hashes.get(), (int)size.line,
-                  new_hashes.begin(), (int)size.line,
-                  [&changes](DiffOp op, int len) mutable {
-        switch (op)
-        {
-            case DiffOp::Keep:
-                changes.push_back({len, 0, 0});
-                break;
-            case DiffOp::Add:
-                changes.back().add += len;
-                break;
-            case DiffOp::Remove:
-                changes.back().del += len;
-                break;
-        }
-    });
-    std::copy(new_hashes.begin(), new_hashes.end(), hashes.get());
-
-    int line = 0;
-    for (auto& change : changes)
+    for (int line = 0; line < (int)size.line; ++line)
     {
-        line += change.keep;
-        if (int del = change.del - change.add; del > 0)
-        {
-            format_with(writer, "\033[{}H\033[{}M", line + 1, del);
-            line -= del;
-        }
-        line += change.del;
-    }
+        auto hash = hash_line(lines[line]); 
+        if (hash == hashes[line])
+            continue;
+        hashes[line] = hash;
 
-    line = 0;
-    for (auto& change : changes)
-    {
-        line += change.keep;
-        for (int i = 0; i < change.add; ++i)
-        {
-            if (int add = change.add - change.del; i == 0 and add > 0)
-                format_with(writer, "\033[{}H\033[{}L", line + 1, add);
-            else
-                format_with(writer, "\033[{}H", line + 1);
+        format_with(writer, "\033[{}H", line + 1);
 
-            ColumnCount pending_move = 0;
-            for (auto& [text, skip, face] : lines[line++].atoms)
+        ColumnCount pending_move = 0;
+        for (auto& [text, skip, face] : lines[line].atoms)
+        {
+            if (text.empty() and skip == 0)
+                continue;
+
+            if (pending_move != 0)
             {
-                if (text.empty() and skip == 0)
-                    continue;
-
-                if (pending_move != 0)
-                {
-                    format_with(writer, "\033[{}C", (int)pending_move);
-                    pending_move = 0;
-                }
-                set_face(face, writer);
-                writer.write(text);
-                if (skip > 3 and face.attributes == Attribute{})
-                {
-                    writer.write("\033[K");
-                    pending_move = skip;
-                }
-                else if (skip > 0)
-                    writer.write(String{' ', skip});
+                format_with(writer, "\033[{}C", (int)pending_move);
+                pending_move = 0;
             }
+            set_face(face, writer);
+            writer.write(text);
+            if (skip > 3 and face.attributes == Attribute{})
+            {
+                writer.write("\033[K");
+                pending_move = skip;
+            }
+            else if (skip > 0)
+                writer.write(String{' ', skip});
         }
     }
 
     // iTerm2 "end synchronized update" sequence
     if (synchronized)
-        writer.write("\033P=2s\033\\");
+        writer.write("\033[?2026l");
 }
 
 constexpr int TerminalUI::default_shift_function_key;