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

@@ -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.
+                    // The transaction has timed out for the xdg toplevel, which means a commit
-                    const old_width = view.current.box.width;
+                    // in response to the configure with the inflight width/height has not yet
-                    const old_height = view.current.box.height;
+                    // 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.width = xdg_toplevel.geometry.width;
-                    view.current.box.height = old_height;
+                    view.current.box.height = xdg_toplevel.geometry.height;
                 },
                 .idle, .committed => {
                     xdg_toplevel.configure_state = .idle;