wayland: Throttle interactive user resize events

Excessive resize events generated during interactive window resizing can cause applications to lag, severely in some cases. Throttle interactive resize events to once per frame callback interval.

src/video/wayland/SDL_waylandwindow.c

@@ -297,7 +297,7 @@ static void SetSurfaceOpaqueRegion(SDL_WindowData *wind, bool is_opaque)
     }
 }
 
-static void ConfigureWindowGeometry(SDL_Window *window)
+static bool ConfigureWindowGeometry(SDL_Window *window)
 {
     SDL_WindowData *data = window->internal;
     const double scale_factor = GetWindowScale(window);
@@ -306,6 +306,17 @@ static void ConfigureWindowGeometry(SDL_Window *window)
     int window_width, window_height;
     bool window_size_changed;
 
+    // Throttle interactive resize events to once per refresh cycle to prevent lag.
+    if (data->resizing) {
+        data->resizing = false;
+
+        if (data->drop_interactive_resizes) {
+            return false;
+        } else {
+            data->drop_interactive_resizes = true;
+        }
+    }
+
     // Set the drawable backbuffer size.
     GetBufferSize(window, &data->current.pixel_width, &data->current.pixel_height);
     const bool buffer_size_changed = data->current.pixel_width != old_pixel_width ||
@@ -454,6 +465,8 @@ static void ConfigureWindowGeometry(SDL_Window *window)
             SDL_SendWindowEvent(window, SDL_EVENT_WINDOW_OCCLUDED, 0, 0);
         }
     }
+
+    return true;
 }
 
 static void CommitLibdecorFrame(SDL_Window *window)
@@ -666,6 +679,8 @@ static void surface_frame_done(void *data, struct wl_callback *cb, uint32_t time
         wl_surface_damage(wind->surface, 0, 0, SDL_MAX_SINT32, SDL_MAX_SINT32);
     }
 
+    wind->drop_interactive_resizes = false;
+
     if (wind->surface_status == WAYLAND_SURFACE_STATUS_WAITING_FOR_FRAME) {
         wind->surface_status = WAYLAND_SURFACE_STATUS_SHOWN;
 
@@ -720,8 +735,9 @@ static void handle_configure_xdg_shell_surface(void *data, struct xdg_surface *x
     SDL_WindowData *wind = (SDL_WindowData *)data;
     SDL_Window *window = wind->sdlwindow;
 
-    ConfigureWindowGeometry(window);
-    xdg_surface_ack_configure(xdg, serial);
+    if (ConfigureWindowGeometry(window)) {
+        xdg_surface_ack_configure(xdg, serial);
+    }
 
     wind->shell_surface.xdg.initial_configure_seen = true;
 }
@@ -745,6 +761,7 @@ static void handle_configure_xdg_toplevel(void *data,
     bool floating = true;
     bool tiled = false;
     bool active = false;
+    bool resizing = false;
     bool suspended = false;
     wl_array_for_each (state, states) {
         switch (*state) {
@@ -756,6 +773,9 @@ static void handle_configure_xdg_toplevel(void *data,
             maximized = true;
             floating = false;
             break;
+        case XDG_TOPLEVEL_STATE_RESIZING:
+            resizing = true;
+            break;
         case XDG_TOPLEVEL_STATE_ACTIVATED:
             active = true;
             break;
@@ -931,6 +951,7 @@ static void handle_configure_xdg_toplevel(void *data,
     wind->suspended = suspended;
     wind->active = active;
     window->tiled = tiled;
+    wind->resizing = resizing;
 
     if (wind->surface_status == WAYLAND_SURFACE_STATUS_WAITING_FOR_CONFIGURE) {
         wind->surface_status = WAYLAND_SURFACE_STATUS_WAITING_FOR_FRAME;
@@ -1099,7 +1120,6 @@ static void decoration_frame_configure(struct libdecor_frame *frame,
 {
     SDL_WindowData *wind = (SDL_WindowData *)user_data;
     SDL_Window *window = wind->sdlwindow;
-    struct libdecor_state *state;
 
     enum libdecor_window_state window_state;
     int width, height;
@@ -1110,6 +1130,7 @@ static void decoration_frame_configure(struct libdecor_frame *frame,
     bool maximized = false;
     bool tiled = false;
     bool suspended = false;
+    bool resizing = false;
     bool floating;
 
     static const enum libdecor_window_state tiled_states = (LIBDECOR_WINDOW_STATE_TILED_LEFT | LIBDECOR_WINDOW_STATE_TILED_RIGHT |
@@ -1123,6 +1144,9 @@ static void decoration_frame_configure(struct libdecor_frame *frame,
         tiled = (window_state & tiled_states) != 0;
 #if SDL_LIBDECOR_CHECK_VERSION(0, 2, 0)
         suspended = (window_state & LIBDECOR_WINDOW_STATE_SUSPENDED) != 0;
+#endif
+#if SDL_LIBDECOR_CHECK_VERSION(0, 3, 0)
+        resizing = (window_state & LIBDECOR_WINDOW_STATE_RESIZING) != 0;
 #endif
     }
     floating = !(fullscreen || maximized || tiled);
@@ -1295,14 +1319,15 @@ static void decoration_frame_configure(struct libdecor_frame *frame,
     wind->suspended = suspended;
     wind->active = active;
     window->tiled = tiled;
+    wind->resizing = resizing;
 
     // Calculate the new window geometry
-    ConfigureWindowGeometry(window);
-
-    // ... then commit the changes on the libdecor side.
-    state = libdecor_state_new(wind->current.logical_width, wind->current.logical_height);
-    libdecor_frame_commit(frame, state, configuration);
-    libdecor_state_free(state);
+    if (ConfigureWindowGeometry(window)) {
+        // ... then commit the changes on the libdecor side.
+        struct libdecor_state *state = libdecor_state_new(wind->current.logical_width, wind->current.logical_height);
+        libdecor_frame_commit(frame, state, configuration);
+        libdecor_state_free(state);
+    }
 
     if (!wind->shell_surface.libdecor.initial_configure_seen) {
         LibdecorGetMinContentSize(frame, &wind->system_limits.min_width, &wind->system_limits.min_height);

src/video/wayland/SDL_waylandwindow.h

@@ -165,7 +165,9 @@ struct SDL_WindowData
     Uint64 last_focus_event_time_ns;
     bool floating;
     bool suspended;
+    bool resizing;
     bool active;
+    bool drop_interactive_resizes;
     bool is_fullscreen;
     bool fullscreen_exclusive;
     bool drop_fullscreen_requests;