From 82d8c67504ab94facc5aa2b312149436c37d3c7d Mon Sep 17 00:00:00 2001
From: Michael Grant <mgrant@grant.org>
Date: Wed, 14 Oct 2026 14:11:55 +0200
Subject: [PATCH] Recalculate window sizes when the terminal reports its pixel
 size.

The reply to CSI 14t updated the client's cell size but not the windows,
which kept the default 16x32 cell size until some other event (a resize, or
any client connecting or exiting) triggered recalculate_sizes(). Images
parsed in the meantime were sized for the wrong cell and drawn at the wrong
size. Recalculate when the reply arrives, and extend the reply test to check
that the window follows the client without any other event.
---
 regress/tty-keys-replies.sh | 20 +++++++++++++++++++-
 tty-keys.c                  |  3 +++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/regress/tty-keys-replies.sh b/regress/tty-keys-replies.sh
index b47e6a8a9..e22442ae4 100755
--- a/regress/tty-keys-replies.sh
+++ b/regress/tty-keys-replies.sh
@@ -12,6 +12,7 @@ TERM=screen
 python3 - "$TEST_TMUX" <<'PY'
 import fcntl
 import os
+import re
 import select
 import struct
 import subprocess
@@ -94,6 +95,13 @@ for name, report in reports:
                 run("new-session", "-d", "-s", "replies", "-x", "80",
                     "-y", "24", "stty raw -echo; exec cat -v")
                 run("set-option", "-g", "status", "off")
+                if name == "pixels":
+                    # Draw the window cell size so it can be read from the
+                    # client's output without running another command, since
+                    # each command's client recalculates the window sizes.
+                    run("set-option", "-g", "status", "on")
+                    run("set-option", "-g", "status-format[0]",
+                        "W=#{window_cell_width}x#{window_cell_height}")
                 run("set-option", "-g", "assume-paste-time", "0")
                 if delivery == "expired":
                     run("set-option", "-s", "escape-time", "100")
@@ -128,6 +136,7 @@ for name, report in reports:
                     chunks = [wire[:-1], wire[-1:]]
                 else:
                     chunks = [wire[i:i+1] for i in range(len(wire))]
+                output = b""
                 for part in chunks[:-1]:
                     os.write(fd, part)
                     time.sleep(.01)
@@ -151,12 +160,21 @@ for name, report in reports:
                 # A trailing key confirms that the entire reply has been
                 # processed, including cases with no extra Escape.
                 os.write(fd, chunks[-1] + b"Z")
+                if name == "pixels":
+                    # With no command run since the reply, the window must
+                    # have followed the client's new cell size by itself.
+                    time.sleep(.3)
+                    while select.select([fd], [], [], .2)[0]:
+                        output += os.read(fd, 65536)
+                    drawn = re.findall(rb"W=(\d+x\d+)", output)
+                    assert drawn and drawn[-1] == b"10x20", (
+                        context, "window cell size", drawn)
                 deadline = time.monotonic() + 5
                 while run("capture-pane", "-p") != expected:
                     assert time.monotonic() < deadline, (context,
                         "reply leaked or input stalled", run("capture-pane", "-p"))
                     if select.select([fd], [], [], .01)[0]:
-                        os.read(fd, 65536)
+                        output += os.read(fd, 65536)
                 actual = state()
                 if delivery in ("invalid", "expired"):
                     assert actual == baseline, (context, "unexpected effect", actual)
diff --git a/tty-keys.c b/tty-keys.c
index b9ca2f019..7031b8796 100644
--- a/tty-keys.c
+++ b/tty-keys.c
@@ -1927,6 +1927,9 @@ tty_keys_winsz(struct tty *tty, const char *buf, size_t len, size_t *size,
 		tty_set_size(tty, tty->sx, tty->sy, char_x, char_y);
 		tty_invalidate(tty);
 
+		/* Windows take their cell size from the clients. */
+		recalculate_sizes();
+
 		tty->flags &= ~TTY_WINSIZEQUERY;
 		return (0);
 	}