From fecfa89a9a8ba1d9704b4d07fe02c16cd20a1644 Mon Sep 17 00:00:00 2001
From: Isaac Freund <mail@isaacfreund.com>
Date: Wed, 13 Mar 2024 15:57:01 +0100
Subject: [PATCH] View: fix SSD desync on consecutive timeouts

If multiple consecutive transaction timeouts occur it is possible for
the SSD borders to become temporarily desynchronized with the size of
the rendered surface.

This is especially noticeable during interactive resize of mpv.

For details on cause/fix, see the new comment in the code.
---
 river/View.zig | 31 +++++++++++++++++++++++++------
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/river/View.zig b/river/View.zig
index 9f7d4bc..311b960 100644
--- a/river/View.zig
+++ b/river/View.zig
@@ -296,13 +296,32 @@ pub fn commitTransaction(view: *Self) void {
                         .acked => xdg_toplevel.configure_state = .timed_out_acked,
                         else => unreachable,
                     }
-                    // The width and height cannot be updated until the client has
-                    // committed a new buffer in response to the configure.
-                    const old_width = view.current.box.width;
-                    const old_height = view.current.box.height;
+
+                    // The transaction has timed out for the xdg toplevel, which means a commit
+                    // in response to the configure with the inflight width/height has not yet
+                    // been made. It may seem that we should therefore leave the current.box
+                    // width/height unchanged. However, this would in fact cause visual glitches.
+                    //
+                    // We must update the dimensions to the current geometry of the
+                    // xdg toplevel here in order to handle the following series of events:
+                    //
+                    // 0. initial state: client has dimensions X
+                    // 1. transaction A sends a configure of size Y
+                    // 2. transaction A times out - saved surfaces are dropped
+                    // 3. transaction B sends a configure of size Z
+                    // 4. client commits buffer of size Y
+                    // 5. transaction B times out - saved surfaces are dropped
+                    //
+                    // If we did not use the current geometry of the toplevel at this point
+                    // we would be rendering the SSD border at initial size X but the surface
+                    // would be rendered at size Y.
+                    if (view.inflight.resizing) {
+                        view.resizeUpdatePosition(xdg_toplevel.geometry.width, xdg_toplevel.geometry.height);
+                    }
+
                     view.current = view.inflight;
-                    view.current.box.width = old_width;
-                    view.current.box.height = old_height;
+                    view.current.box.width = xdg_toplevel.geometry.width;
+                    view.current.box.height = xdg_toplevel.geometry.height;
                 },
                 .idle, .committed => {
                     xdg_toplevel.configure_state = .idle;