From 42f615fe6092c93e228b29ec9a283ddc425119c7 Mon Sep 17 00:00:00 2001
From: YaoBing Xiao <xiaoyaobing@uniontech.com>
Date: Sat, 6 Jun 2026 16:36:52 +0800
Subject: [PATCH] tinywl: stabilize resize from top-left edges

When resizing from the left or top edges, wait until the client
commits its resized buffer before updating the scene node position.

This keeps the unmoved edge anchored to the committed geometry instead
of the requested configure size.

This fixes visible jitter when resizing weston-terminal with the mouse
from the top-left corner, where the terminal can quantize its size and
otherwise cause the window position to oscillate during interactive resize.
---
 tinywl/tinywl.c | 36 +++++++++++++++++++++++++++++-------
 1 file changed, 29 insertions(+), 7 deletions(-)

diff --git a/tinywl/tinywl.c b/tinywl/tinywl.c
index fe242e1a9..4bee846b3 100644
--- a/tinywl/tinywl.c
+++ b/tinywl/tinywl.c
@@ -399,6 +399,30 @@ static void process_cursor_move(struct tinywl_server *server) {
 		server->cursor->y - server->grab_y);
 }
 
+static void update_resize_position(struct tinywl_toplevel *toplevel) {
+	struct tinywl_server *server = toplevel->server;
+	if (server->cursor_mode != TINYWL_CURSOR_RESIZE ||
+			server->grabbed_toplevel != toplevel) {
+		return;
+	}
+
+	struct wlr_box *geo_box = &toplevel->xdg_toplevel->base->geometry;
+	int lx = server->grab_geobox.x;
+	int ly = server->grab_geobox.y;
+
+	if (server->resize_edges & WLR_EDGE_LEFT) {
+		lx = server->grab_geobox.x + server->grab_geobox.width -
+			geo_box->width;
+	}
+	if (server->resize_edges & WLR_EDGE_TOP) {
+		ly = server->grab_geobox.y + server->grab_geobox.height -
+			geo_box->height;
+	}
+
+	wlr_scene_node_set_position(&toplevel->scene_tree->node,
+		lx - geo_box->x, ly - geo_box->y);
+}
+
 static void process_cursor_resize(struct tinywl_server *server) {
 	/*
 	 * Resizing the grabbed toplevel can be a little bit complicated, because we
@@ -406,9 +430,8 @@ static void process_cursor_resize(struct tinywl_server *server) {
 	 * toplevel on one or two axes, but can also move the toplevel if you resize
 	 * from the top or left edges (or top-left corner).
 	 *
-	 * Note that some shortcuts are taken here. In a more fleshed-out
-	 * compositor, you'd wait for the client to prepare a buffer at the new
-	 * size, then commit any movement that was prepared.
+	 * Movement is applied on commit so that surfaces which quantize their size
+	 * can keep the unmoved edge stable.
 	 */
 	struct tinywl_toplevel *toplevel = server->grabbed_toplevel;
 	double border_x = server->cursor->x - server->grab_x;
@@ -441,10 +464,6 @@ static void process_cursor_resize(struct tinywl_server *server) {
 		}
 	}
 
-	struct wlr_box *geo_box = &toplevel->xdg_toplevel->base->geometry;
-	wlr_scene_node_set_position(&toplevel->scene_tree->node,
-		new_left - geo_box->x, new_top - geo_box->y);
-
 	int new_width = new_right - new_left;
 	int new_height = new_bottom - new_top;
 	wlr_xdg_toplevel_set_size(toplevel->xdg_toplevel, new_width, new_height);
@@ -701,7 +720,10 @@ static void xdg_toplevel_commit(struct wl_listener *listener, void *data) {
 		 * configures the xdg_toplevel with 0,0 size to let the client pick the
 		 * dimensions itself. */
 		wlr_xdg_toplevel_set_size(toplevel->xdg_toplevel, 0, 0);
+		return;
 	}
+
+	update_resize_position(toplevel);
 }
 
 static void xdg_toplevel_destroy(struct wl_listener *listener, void *data) {