Merge pull request #22172 from bfredl/cells

perf(ui): mitigate redraw latency regression from TUI refactor

src/nvim/api/ui.c

@@ -202,6 +202,7 @@ void nvim_ui_attach(uint64_t channel_id, Integer width, Integer height, Dictiona
   data->flushed_events = false;
   data->ncalls_pos = NULL;
   data->ncalls = 0;
+  data->ncells_pending = 0;
   data->buf_wptr = data->buf;
   data->temp_buf = NULL;
   data->wildmenu_active = false;
@@ -854,18 +855,25 @@ void remote_ui_raw_line(UI *ui, Integer grid, Integer row, Integer startcol, Int
             mpack_uint(buf, repeat);
           }
         }
+        data->ncells_pending += MIN(repeat, 2);
         last_hl = attrs[i];
         repeat = 0;
       }
     }
     if (endcol < clearcol) {
       nelem++;
+      data->ncells_pending += 1;
       mpack_array(buf, 3);
       mpack_str(buf, " ");
       mpack_uint(buf, (uint32_t)clearattr);
       mpack_uint(buf, (uint32_t)(clearcol - endcol));
     }
     mpack_w2(&lenpos, nelem);
+
+    if (data->ncells_pending > 500) {
+      // pass of cells to UI to let it start processing them
+      remote_ui_flush_buf(ui);
+    }
   } else {
     for (int i = 0; i < endcol - startcol; i++) {
       remote_ui_cursor_goto(ui, row, startcol + i);
@@ -917,6 +925,8 @@ void remote_ui_flush_buf(UI *ui)
   // we have sent events to the client, but possibly not yet the final "flush"
   // event.
   data->flushed_events = true;
+
+  data->ncells_pending = 0;
 }
 
 /// An intentional flush (vsync) when Nvim is finished redrawing the screen

src/nvim/option_defs.h

@@ -630,6 +630,8 @@ EXTERN unsigned rdb_flags;
 #define RDB_NOTHROTTLE         0x002
 #define RDB_INVALID            0x004
 #define RDB_NODELTA            0x008
+#define RDB_LINE               0x010
+#define RDB_FLUSH              0x020
 
 EXTERN long p_rdt;            // 'redrawtime'
 EXTERN long p_re;             // 'regexpengine'

src/nvim/optionstr.c

@@ -125,7 +125,8 @@ static char *(p_spo_values[]) = { "camel", "noplainbuffer", NULL };
 static char *(p_icm_values[]) = { "nosplit", "split", NULL };
 static char *(p_jop_values[]) = { "stack", "view", NULL };
 static char *(p_tpf_values[]) = { "BS", "HT", "FF", "ESC", "DEL", "C0", "C1", NULL };
-static char *(p_rdb_values[]) = { "compositor", "nothrottle", "invalid", "nodelta", NULL };
+static char *(p_rdb_values[]) = { "compositor", "nothrottle", "invalid", "nodelta", "line",
+                                  "flush", NULL };
 static char *(p_sloc_values[]) = { "last", "statusline", "tabline", NULL };
 
 /// All possible flags for 'shm'.

src/nvim/ui.c

@@ -419,7 +419,7 @@ void ui_line(ScreenGrid *grid, int row, int startcol, int endcol, int clearcol,
                    (const sattr_T *)grid->attrs + off);
 
   // 'writedelay': flush & delay each time.
-  if (p_wd && !(rdb_flags & RDB_COMPOSITOR)) {
+  if (p_wd && (rdb_flags & RDB_LINE)) {
     // If 'writedelay' is active, set the cursor to indicate what was drawn.
     ui_call_grid_cursor_goto(grid->handle, row,
                              MIN(clearcol, (int)grid->cols - 1));
@@ -510,6 +510,10 @@ void ui_flush(void)
     pending_has_mouse = has_mouse;
   }
   ui_call_flush();
+
+  if (p_wd && (rdb_flags & RDB_FLUSH)) {
+    os_microdelay((uint64_t)labs(p_wd) * 1000U, true);
+  }
 }
 
 /// Check if 'mouse' is active for the current mode

src/nvim/ui.h

@@ -79,6 +79,8 @@ typedef struct {
   uint32_t ncalls;  ///< number of calls made to the current event (plus one for the name!)
   bool flushed_events;  ///< events where sent to client without "flush" event
 
+  size_t ncells_pending;  ///< total number of cells since last buffer flush
+
   int hl_id;  // Current highlight for legacy put event.
   Integer cursor_row, cursor_col;  // Intended visible cursor position.