Send individual grids to UIs with event "grid_resize"

The grids get allocated a handle (very naive at the moment) and these
handles are sent with every event to the external UIs.  Works for one
window at the moment.

Use neovim/python-gui#36 to test. It currently creates separate windows
for each grid. `:sp` seems to work, but `:vs` crashes.

src/nvim/api/ui.c

@@ -270,6 +270,10 @@ static void remote_ui_grid_resize(UI *ui, Integer grid,
   Array args = ARRAY_DICT_INIT;
   if (ui->ui_ext[kUINewgrid]) {
     ADD(args, INTEGER_OBJ(grid));
+  } else if (grid != 1) {
+    // calling grid_resize with a grid other than the global when
+    // the remote ui is not managing grids should not send the event
+    return;
   }
   ADD(args, INTEGER_OBJ(width));
   ADD(args, INTEGER_OBJ(height));

src/nvim/screen.c

@@ -128,6 +128,14 @@ StlClickDefinition *tab_page_click_defs = NULL;
 
 long tab_page_click_defs_size = 0;
 
+/// The last handle that was assigned to a ScreenGrid. 1 is reserved for
+/// the default_grid.
+/// TODO(utkarshme): Numbers can be recycled after grid destruction.
+static int last_handle = 1;
+
+/// Whether to call "ui_call_grid_resize" in win_grid_alloc
+static int send_grid_resize;
+
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "screen.c.generated.h"
 #endif
@@ -422,6 +430,7 @@ void update_screen(int type)
       win_redr_status(wp);
     }
   }
+  send_grid_resize = false;
   end_search_hl();
   // May need to redraw the popup menu.
   if (pum_drawn()) {
@@ -654,7 +663,7 @@ static void win_update(win_T *wp)
 
   type = wp->w_redr_type;
 
-  window_grid_alloc(wp, false);
+  win_grid_alloc(wp, false);
 
   if (type == NOT_VALID) {
     wp->w_redr_status = TRUE;
@@ -2221,7 +2230,7 @@ win_line (
   row = startrow;
 
   // allocate window grid if not already
-  window_grid_alloc(wp, true);
+  win_grid_alloc(wp, true);
 
   /*
    * To speed up the loop below, set extra_check when there is linebreak,
@@ -5831,18 +5840,28 @@ int screen_valid(int doclear)
 /// (re)allocate a window grid if size changed
 /// If "doclear" is true, clear the screen if resized.
 // TODO(utkarshme): Think of a better name, place
-void window_grid_alloc(win_T *wp, int doclear)
+void win_grid_alloc(win_T *wp, int doclear)
 {
-  if (wp->w_grid.ScreenLines != NULL
-      && wp->w_grid.Rows == wp->w_height
-      && wp->w_grid.Columns == wp->w_width) {
-    return;
-  }
+  if (wp->w_grid.ScreenLines == NULL
+      || wp->w_grid.Rows != wp->w_height
+      || wp->w_grid.Columns != wp->w_width) {
+    grid_alloc(&wp->w_grid, wp->w_height, wp->w_width, doclear);
+
+    // only assign a grid handle if not already
+    if (wp->w_grid.handle == 0) {
+      wp->w_grid.handle = ++last_handle;
+    }
+
+    wp->w_grid.OffsetRow = wp->w_winrow;
+    wp->w_grid.OffsetColumn = wp->w_wincol;
 
-  grid_alloc(&wp->w_grid, wp->w_height, wp->w_width, doclear);
+    wp->w_grid.was_resized = true;
+  }
 
-  wp->w_grid.OffsetRow = wp->w_winrow;
-  wp->w_grid.OffsetColumn = wp->w_wincol;
+  if (send_grid_resize || wp->w_grid.was_resized) {
+    ui_call_grid_resize(wp->w_grid.handle, wp->w_grid.Columns, wp->w_grid.Rows);
+    wp->w_grid.was_resized = false;
+  }
 }
 
 /*
@@ -5936,6 +5955,7 @@ void screenalloc(bool doclear)
 
   default_grid.OffsetRow = 0;
   default_grid.OffsetColumn = 0;
+  default_grid.handle = 1;
 
   must_redraw = CLEAR;          /* need to clear the screen later */
   if (doclear)
@@ -5960,7 +5980,7 @@ void screenalloc(bool doclear)
 void grid_alloc(ScreenGrid *grid, int rows, int columns, bool copy)
 {
   int new_row, old_row;
-  ScreenGrid new = { 0 };
+  ScreenGrid new = *grid;
 
   size_t ncells = (size_t)((rows+1) * columns);
   new.ScreenLines = xmalloc(ncells * sizeof(schar_T));
@@ -6247,7 +6267,7 @@ int grid_ins_lines(ScreenGrid *grid, int row, int line_count, int end,
     }
   }
 
-  ui_call_grid_scroll(1, row, end, col, col+width, -line_count, 0);
+  ui_call_grid_scroll(grid->handle, row, end, col, col+width, -line_count, 0);
 
   return OK;
 }
@@ -6299,7 +6319,7 @@ int grid_del_lines(ScreenGrid *grid, int row, int line_count, int end,
     }
   }
 
-  ui_call_grid_scroll(1, row, end, col, col+width, line_count, 0);
+  ui_call_grid_scroll(grid->handle, row, end, col, col+width, line_count, 0);
 
   return OK;
 }
@@ -7052,6 +7072,8 @@ void screen_resize(int width, int height)
   default_grid.Rows = screen_Rows;
   default_grid.Columns = screen_Columns;
 
+  send_grid_resize = true;
+
   /* The window layout used to be adjusted here, but it now happens in
    * screenalloc() (also invoked from screenclear()).  That is because the
    * "busy" check above may skip this, but not screenalloc(). */

src/nvim/types.h

@@ -39,6 +39,8 @@ typedef struct {
   // offsets for the grid relative to the screen
   int OffsetRow;
   int OffsetColumn;
+
+  int was_resized;
 } ScreenGrid;
 
 #endif  // NVIM_TYPES_H

src/nvim/ui.c

@@ -317,10 +317,13 @@ void ui_set_ext_option(UI *ui, UIExtension ext, bool active)
 void ui_line(ScreenGrid *grid, int row, int startcol, int endcol, int clearcol, int clearattr)
 {
   size_t off = grid->LineOffset[row] + (size_t)startcol;
-  UI_CALL(raw_line, 1, grid->OffsetRow + row, grid->OffsetColumn + startcol,
-          grid->OffsetColumn + endcol, grid->OffsetColumn + clearcol,
-          clearattr, (const schar_T *)grid->ScreenLines + off,
-          (const schar_T *)grid->ScreenAttrs + off);
+  int row_off = ui_is_external(kUIMultigrid) ? 0 : grid->OffsetRow;
+  int col_off = ui_is_external(kUIMultigrid) ? 0 : grid->OffsetColumn;
+
+  UI_CALL(raw_line, grid->handle, row_off + row, col_off + startcol,
+          col_off + endcol, col_off + clearcol, clearattr,
+          (const schar_T *)grid->ScreenLines + off,
+          (const sattr_T *)grid->ScreenAttrs + off);
 
   if (p_wd) {  // 'writedelay': flush & delay each time.
     int old_row = row, old_col = col;

src/nvim/ui.h

@@ -16,6 +16,7 @@ typedef enum {
   kUIWildmenu,
 #define kUIGlobalCount (kUIWildmenu+1)
   kUINewgrid,
+  kUIMultigrid,
   kUIHlState,
   kUIExtCount,
 } UIExtension;
@@ -26,6 +27,7 @@ EXTERN const char *ui_ext_names[] INIT(= {
   "ext_tabline",
   "ext_wildmenu",
   "ext_newgrid",
+  "ext_multigrid",
   "ext_hlstate",
 });
 

src/nvim/window.c

@@ -4222,7 +4222,7 @@ void win_setheight_win(int height, win_T *win)
   }
 
   frame_setheight(win->w_frame, height + win->w_status_height);
-  window_grid_alloc(win, false);
+  win_grid_alloc(win, false);
 
   /* recompute the window positions */
   row = win_comp_pos();
@@ -4419,7 +4419,7 @@ void win_setwidth_win(int width, win_T *wp)
   }
 
   frame_setwidth(wp->w_frame, width + wp->w_vsep_width);
-  window_grid_alloc(wp, false);
+  win_grid_alloc(wp, false);
 
   /* recompute the window positions */
   (void)win_comp_pos();