From 3565cbd636dacf15049504d686219b787783733c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Thu, 6 Oct 2022 17:09:32 +0200
Subject: [PATCH] render: performance improvements during interactive resize

Instead of copying the entire grid when an interactive resize is
started, stash the complete grid (to be used in the final reflow).

Copy the current viewport only, to be used during the interactive
resize.

This gets rid of the initial "pause" when snapshotting the grid when
an interactive resize is started.
---
 render.c | 44 ++++++++++++++++++++++++++++++++++++++------
 1 file changed, 38 insertions(+), 6 deletions(-)

diff --git a/render.c b/render.c
index 034c9946..d2fce8b0 100644
--- a/render.c
+++ b/render.c
@@ -3900,13 +3900,45 @@ maybe_resize(struct terminal *term, int width, int height, bool force)
      * the original grid, before the resize started.
      */
     if (term->window->is_resizing && term->render.resizing.grid == NULL) {
-        /*
-         * TODO: snapshotting a large grid is slow. To improve, move
-         * normal -> resizing.grid, and instantiate a small (screen
-         * sized) new “normal”
-         */
-        term->render.resizing.grid = grid_snapshot(&term->normal);
+        /* Stash the current ‘normal’ grid, as-is, to be used when
+         * doing the final reflow */
         term->render.resizing.screen_rows = term->rows;
+        term->render.resizing.grid = xmalloc(sizeof(*term->render.resizing.grid));
+        *term->render.resizing.grid = term->normal;
+
+
+        /*
+         * Copy the current viewport to a new grid that will be used
+         * during the resize. For now, throw away sixels and OSC-8
+         * URLs. They’ll be "restored" when we do the final reflow.
+         *
+         * TODO:
+         *  - sixels?
+         *  - OSC-8?
+         */
+        struct grid g = {
+            .num_rows = 1 << (32 - __builtin_clz(term->rows - 1)),
+            .num_cols = term->cols,
+            .offset = 0,
+            .view = 0,
+            .cursor = term->normal.cursor,
+            .saved_cursor = term->normal.saved_cursor,
+            .rows = xcalloc(g.num_rows, sizeof(g.rows[0])),
+            .cur_row = NULL,
+            .scroll_damage = tll_init(),
+            .sixel_images = tll_init(),
+            .kitty_kbd = term->normal.kitty_kbd,
+        };
+
+        for (size_t i = 0, j = term->normal.view; i < term->rows;
+             i++, j = (j + 1) & (term->normal.num_rows - 1))
+        {
+            g.rows[i] = grid_row_alloc(term->cols, false);
+            memcpy(g.rows[i]->cells, term->normal.rows[j]->cells,
+                   term->cols * sizeof(g.rows[i]->cells[0]));
+        }
+
+        term->normal = g;
     }
 
     /* Screen rows/cols before resize */