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

1 files changed, 25 insertions, 61 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)
+        format_with(writer, "\033[{}H", line + 1);
+
+        ColumnCount pending_move = 0;
+        for (auto& [text, skip, face] : lines[line].atoms)
         {
-            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);
+            if (text.empty() and skip == 0)
+                continue;
 
-            ColumnCount pending_move = 0;
-            for (auto& [text, skip, face] : lines[line++].atoms)
+            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{})
             {
-                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});
+                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;