wayland: Always create a viewport for the window if available

Viewports decouple the buffer from the window size and avoids the window geometry hacks used to prevent problems if a buffer with an old size in the pipeline ends up being committed.

Fixes an invalid geometry warning and incorrect overview size for fullscreen windows on GNOME, and avoids flicker when entering/exiting fullscreen or moving the window between scaled and non-scaled displays.

src/video/wayland/SDL_waylandwindow.c

@@ -118,47 +118,12 @@ static void GetFullScreenDimensions(SDL_Window *window, int *width, int *height,
     }
 }
 
-SDL_FORCE_INLINE SDL_bool SurfaceScaleIsFractional(SDL_Window *window)
-{
-    SDL_WindowData *data = window->driverdata;
-    return !FloatEqual(SDL_roundf(data->scale_factor), data->scale_factor);
-}
-
 SDL_FORCE_INLINE SDL_bool FullscreenModeEmulation(SDL_Window *window)
 {
     return (window->flags & SDL_WINDOW_FULLSCREEN) &&
            ((window->flags & SDL_WINDOW_FULLSCREEN_DESKTOP) != SDL_WINDOW_FULLSCREEN_DESKTOP);
 }
 
-static SDL_bool NeedViewport(SDL_Window *window)
-{
-    SDL_WindowData *wind = window->driverdata;
-    SDL_VideoData *video = wind->waylandData;
-    SDL_VideoDisplay *display = SDL_GetDisplayForWindow(window);
-    SDL_WaylandOutputData *output = display ? ((SDL_WaylandOutputData *)display->driverdata) : NULL;
-    const int output_width = wind->fs_output_width ? wind->fs_output_width : (output ? output->width : wind->window_width);
-    const int output_height = wind->fs_output_height ? wind->fs_output_height : (output ? output->height : wind->window_height);
-    int fs_width, fs_height;
-
-    /*
-     * A viewport is only required when scaling is enabled and:
-     *  - A fullscreen mode is being emulated and the mode does not match the logical desktop dimensions.
-     *  - The desktop uses fractional scaling and the high-DPI flag is set.
-     */
-    if (video->viewporter) {
-        if (FullscreenModeEmulation(window)) {
-            GetFullScreenDimensions(window, &fs_width, &fs_height, NULL, NULL);
-            if (fs_width != output_width || fs_height != output_height) {
-                return SDL_TRUE;
-            }
-        } else if (SurfaceScaleIsFractional(window) && (window->flags & SDL_WINDOW_ALLOW_HIGHDPI)) {
-            return SDL_TRUE;
-        }
-    }
-
-    return SDL_FALSE;
-}
-
 static void GetBufferSize(SDL_Window *window, int *width, int *height)
 {
     SDL_WindowData *data = window->driverdata;
@@ -167,15 +132,12 @@ static void GetBufferSize(SDL_Window *window, int *width, int *height)
 
     if (FullscreenModeEmulation(window)) {
         GetFullScreenDimensions(window, NULL, NULL, &buf_width, &buf_height);
-    } else if (NeedViewport(window)) {
+    } else if (data->draw_viewport) {
         /* Round fractional backbuffer sizes halfway away from zero. */
         buf_width = (int)SDL_lroundf(window->w * data->scale_factor);
         buf_height = (int)SDL_lroundf(window->h * data->scale_factor);
     } else {
-        /*
-         * Integer scaled windowed or fullscreen with no viewport
-         *
-         * Round the scale factor up in the unlikely scenario of a compositor
+        /* Round the scale factor up in the unlikely scenario of a compositor
          * that supports fractional scaling, but not viewports.
          */
         int scale_factor = (int)SDL_ceilf(data->scale_factor);
@@ -192,31 +154,6 @@ static void GetBufferSize(SDL_Window *window, int *width, int *height)
     }
 }
 
-static void SetDrawSurfaceViewport(SDL_Window *window, int src_width, int src_height, int dst_width, int dst_height)
-{
-    SDL_WindowData *wind = window->driverdata;
-    SDL_VideoData *video = wind->waylandData;
-
-    if (video->viewporter) {
-        if (!wind->draw_viewport) {
-            wind->draw_viewport = wp_viewporter_get_viewport(video->viewporter, wind->surface);
-        }
-
-        wp_viewport_set_source(wind->draw_viewport, wl_fixed_from_int(-1), wl_fixed_from_int(-1), wl_fixed_from_int(-1), wl_fixed_from_int(-1));
-        wp_viewport_set_destination(wind->draw_viewport, dst_width, dst_height);
-    }
-}
-
-static void UnsetDrawSurfaceViewport(SDL_Window *window)
-{
-    SDL_WindowData *wind = window->driverdata;
-
-    if (wind->draw_viewport) {
-        wp_viewport_destroy(wind->draw_viewport);
-        wind->draw_viewport = NULL;
-    }
-}
-
 static void ConfigureWindowGeometry(SDL_Window *window)
 {
     SDL_WindowData *data = window->driverdata;
@@ -240,7 +177,7 @@ static void ConfigureWindowGeometry(SDL_Window *window)
                                      0, 0);
     }
 
-    if (FullscreenModeEmulation(window) && NeedViewport(window)) {
+    if (FullscreenModeEmulation(window) && data->draw_viewport) {
         int fs_width, fs_height;
         const int output_width = data->fs_output_width ? data->fs_output_width : (output ? output->width : data->window_width);
         const int output_height = data->fs_output_height ? data->fs_output_height : (output ? output->height : data->window_height);
@@ -252,8 +189,7 @@ static void ConfigureWindowGeometry(SDL_Window *window)
 
             /* Set the buffer scale to 1 since a viewport will be used. */
             wl_surface_set_buffer_scale(data->surface, 1);
-            SetDrawSurfaceViewport(window, data->drawable_width, data->drawable_height,
-                                   output_width, output_height);
+            wp_viewport_set_destination(data->draw_viewport, output_width, output_height);
 
             data->window_width = output_width;
             data->window_height = output_height;
@@ -265,12 +201,10 @@ static void ConfigureWindowGeometry(SDL_Window *window)
         window_size_changed = data->window_width != window->w || data->window_height != window->h;
 
         if (window_size_changed || drawable_size_changed) {
-            if (NeedViewport(window)) {
+            if (data->draw_viewport) {
                 wl_surface_set_buffer_scale(data->surface, 1);
-                SetDrawSurfaceViewport(window, data->drawable_width, data->drawable_height, window->w, window->h);
+                wp_viewport_set_destination(data->draw_viewport, window->w, window->h);
             } else {
-                UnsetDrawSurfaceViewport(window);
-
                 if (!FullscreenModeEmulation(window)) {
                     /* Round to the next integer in case of a fractional value. */
                     wl_surface_set_buffer_scale(data->surface, (int32_t)SDL_ceilf(data->scale_factor));
@@ -293,8 +227,11 @@ static void ConfigureWindowGeometry(SDL_Window *window)
      * need to be recalculated if the output size has changed.
      */
     if (window_size_changed) {
-        /* libdecor does this internally on frame commits, so it's only needed for xdg surfaces. */
-        if (data->shell_surface_type != WAYLAND_SURFACE_LIBDECOR &&
+        /* XXX: This is a hack and only set on the xdg-toplevel path when viewports
+         *      aren't supported to avoid a potential protocol violation if a buffer
+         *      with an old size is committed.
+         */
+        if (!data->draw_viewport && data->shell_surface_type == WAYLAND_SURFACE_XDG_TOPLEVEL &&
             viddata->shell.xdg && data->shell_surface.xdg.surface) {
             xdg_surface_set_window_geometry(data->shell_surface.xdg.surface, 0, 0, data->window_width, data->window_height);
         }
@@ -1426,9 +1363,6 @@ void Wayland_ShowWindow(_THIS, SDL_Window *window)
                                                      &decoration_listener,
                                                      window);
         }
-
-        /* Set the geometry */
-        xdg_surface_set_window_geometry(data->shell_surface.xdg.surface, 0, 0, data->window_width, data->window_height);
     } else {
         /* Nothing to see here, just commit. */
         wl_surface_commit(data->surface);
@@ -2041,6 +1975,13 @@ int Wayland_CreateWindow(_THIS, SDL_Window *window)
 
     SDL_WAYLAND_register_surface(data->surface);
 
+    if (c->viewporter) {
+        data->draw_viewport = wp_viewporter_get_viewport(c->viewporter, data->surface);
+        wp_viewport_set_source(data->draw_viewport,
+                               wl_fixed_from_int(-1), wl_fixed_from_int(-1),
+                               wl_fixed_from_int(-1), wl_fixed_from_int(-1));
+    }
+
     /* Must be called before EGL configuration to set the drawable backbuffer size. */
     ConfigureWindowGeometry(window);