perf(mouse): only generate <MouseMove> for a new cell positon (#31103)

Problem: Can receive dozens of <MouseMove> events for same cell position. #30965
Solution: Leverage check_multiclick() to detect if cell position is unchanged.

src/nvim/os/input.c

@@ -290,8 +290,9 @@ size_t input_enqueue(String keys)
       = trans_special(&ptr, (size_t)(end - ptr), (char *)buf, FSK_KEYCODE, true, NULL);
 
     if (new_size) {
-      new_size = handle_mouse_event(&ptr, buf, new_size);
+      if ((new_size = handle_mouse_event(&ptr, buf, new_size))) {
         input_enqueue_raw((char *)buf, new_size);
+      }
       continue;
     }
 
@@ -326,7 +327,7 @@ size_t input_enqueue(String keys)
   return rv;
 }
 
-static uint8_t check_multiclick(int code, int grid, int row, int col)
+static uint8_t check_multiclick(int code, int grid, int row, int col, bool *skip_event)
 {
   static int orig_num_clicks = 0;
   static int orig_mouse_code = 0;
@@ -335,24 +336,29 @@ static uint8_t check_multiclick(int code, int grid, int row, int col)
   static int orig_mouse_row = 0;
   static uint64_t orig_mouse_time = 0;  // time of previous mouse click
 
-  if ((code >= KE_MOUSEDOWN && code <= KE_MOUSERIGHT) || code == KE_MOUSEMOVE) {
+  if (code >= KE_MOUSEDOWN && code <= KE_MOUSERIGHT) {
     return 0;
   }
 
-  // For click events the number of clicks is updated.
+  bool no_move = orig_mouse_grid == grid && orig_mouse_col == col && orig_mouse_row == row;
-  if (code == KE_LEFTMOUSE || code == KE_RIGHTMOUSE || code == KE_MIDDLEMOUSE
+
+  if (code == KE_MOUSEMOVE) {
+    if (no_move) {
+      *skip_event = true;
+      return 0;
+    }
+  } else if (code == KE_LEFTMOUSE || code == KE_RIGHTMOUSE || code == KE_MIDDLEMOUSE
              || code == KE_X1MOUSE || code == KE_X2MOUSE) {
+    // For click events the number of clicks is updated.
     uint64_t mouse_time = os_hrtime();    // time of current mouse click (ns)
     // compute the time elapsed since the previous mouse click and
     // convert p_mouse from ms to ns
     uint64_t timediff = mouse_time - orig_mouse_time;
     uint64_t mouset = (uint64_t)p_mouset * 1000000;
     if (code == orig_mouse_code
+        && no_move
         && timediff < mouset
-        && orig_num_clicks != 4
+        && orig_num_clicks != 4) {
-        && orig_mouse_grid == grid
-        && orig_mouse_col == col
-        && orig_mouse_row == row) {
       orig_num_clicks++;
     } else {
       orig_num_clicks = 1;
@@ -367,6 +373,7 @@ static uint8_t check_multiclick(int code, int grid, int row, int col)
   orig_mouse_row = row;
 
   uint8_t modifiers = 0;
+  if (code != KE_MOUSEMOVE) {
     if (orig_num_clicks == 2) {
       modifiers |= MOD_MASK_2CLICK;
     } else if (orig_num_clicks == 3) {
@@ -374,6 +381,7 @@ static uint8_t check_multiclick(int code, int grid, int row, int col)
     } else if (orig_num_clicks == 4) {
       modifiers |= MOD_MASK_4CLICK;
     }
+  }
   return modifiers;
 }
 
@@ -421,8 +429,12 @@ static unsigned handle_mouse_event(const char **ptr, uint8_t *buf, unsigned bufs
     *ptr += advance;
   }
 
+  bool skip_event = false;
   uint8_t modifiers = check_multiclick(mouse_code, mouse_grid,
-                                       mouse_row, mouse_col);
+                                       mouse_row, mouse_col, &skip_event);
+  if (skip_event) {
+    return 0;
+  }
 
   if (modifiers) {
     if (buf[1] != KS_MODIFIER) {
@@ -443,7 +455,11 @@ static unsigned handle_mouse_event(const char **ptr, uint8_t *buf, unsigned bufs
 
 void input_enqueue_mouse(int code, uint8_t modifier, int grid, int row, int col)
 {
-  modifier |= check_multiclick(code, grid, row, col);
+  bool skip_event = false;
+  modifier |= check_multiclick(code, grid, row, col, &skip_event);
+  if (skip_event) {
+    return;
+  }
   uint8_t buf[7];
   uint8_t *p = buf;
   if (modifier) {

test/functional/ui/mouse_spec.lua

@@ -1908,19 +1908,33 @@ describe('ui/mouse/input', function()
     eq(0, api.nvim_get_var('mouse_up2'))
   end)
 
-  it('<MouseMove> is not translated into multiclicks and can be mapped', function()
+  it('<MouseMove> to different locations can be mapped', function()
     api.nvim_set_var('mouse_move', 0)
     api.nvim_set_var('mouse_move2', 0)
     command('nnoremap <MouseMove> <Cmd>let g:mouse_move += 1<CR>')
     command('nnoremap <2-MouseMove> <Cmd>let g:mouse_move2 += 1<CR>')
-    feed('<MouseMove><0,0>')
+    feed('<MouseMove><1,0>')
-    feed('<MouseMove><0,0>')
+    feed('<MouseMove><2,0>')
-    api.nvim_input_mouse('move', '', '', 0, 0, 0)
+    api.nvim_input_mouse('move', '', '', 0, 0, 3)
-    api.nvim_input_mouse('move', '', '', 0, 0, 0)
+    api.nvim_input_mouse('move', '', '', 0, 0, 4)
     eq(4, api.nvim_get_var('mouse_move'))
     eq(0, api.nvim_get_var('mouse_move2'))
   end)
 
+  it('<MouseMove> to same location does not generate events #31103', function()
+    api.nvim_input_mouse('move', '', '', 0, 0, 3)
+    api.nvim_set_var('mouse_move', 0)
+    api.nvim_set_var('mouse_move2', 0)
+    command('nnoremap <MouseMove> <Cmd>let g:mouse_move += 1<CR>')
+    command('nnoremap <2-MouseMove> <Cmd>let g:mouse_move2 += 1<CR>')
+    feed('<MouseMove><3,0>')
+    feed('<MouseMove><3,0>')
+    api.nvim_input_mouse('move', '', '', 0, 0, 3)
+    api.nvim_input_mouse('move', '', '', 0, 0, 3)
+    eq(0, api.nvim_get_var('mouse_move'))
+    eq(0, api.nvim_get_var('mouse_move2'))
+  end)
+
   it('feeding <MouseMove> in Normal mode does not use uninitialized memory #19480', function()
     feed('<MouseMove>')
     n.poke_eventloop()