video: wayland: Set the surface damage region when using fullscreen viewports

When using emulated display modes, the output size is often larger than the drawable buffer.  As the surface damage region is automatically calculated from the smaller drawable buffer size, the damage region needs to be manually set to cover the entire viewport region or visual repaint artifacts can result.

src/video/wayland/SDL_waylandwindow.c

@@ -241,6 +241,11 @@ ConfigureViewport(SDL_Window *window)
         GetFullScreenDimensions(window, &fs_width, &fs_height, &src_width, &src_height);
         SetViewport(window, src_width, src_height, output->width, output->height);
 
+        data->damage_region.x = 0;
+        data->damage_region.y = 0;
+        data->damage_region.w = output->width;
+        data->damage_region.h = output->height;
+
         data->pointer_scale_x = (float)fs_width / (float)output->width;
         data->pointer_scale_y = (float)fs_height / (float)output->height;
     } else {
@@ -253,6 +258,8 @@ ConfigureViewport(SDL_Window *window)
             UnsetViewport(window);
         }
 
+        SDL_zero(data->damage_region);
+
         data->pointer_scale_x = 1.0f;
         data->pointer_scale_y = 1.0f;
     }
@@ -400,6 +407,11 @@ handle_surface_frame_done(void *data, struct wl_callback *cb, uint32_t time)
     SDL_WindowData *wind = (SDL_WindowData *) data;
     SDL_AtomicSet(&wind->swap_interval_ready, 1);  /* mark window as ready to present again. */
 
+    if (!SDL_RectEmpty(&wind->damage_region)) {
+        wl_surface_damage(wind->surface, wind->damage_region.x, wind->damage_region.y,
+                          wind->damage_region.w, wind->damage_region.h);
+    }
+
     /* reset this callback to fire again once a new frame was presented and compositor wants the next one. */
     wind->frame_callback = wl_surface_frame(wind->frame_surface_wrapper);
     wl_callback_destroy(cb);

src/video/wayland/SDL_waylandwindow.h

@@ -90,6 +90,7 @@ typedef struct {
     float pointer_scale_x;
     float pointer_scale_y;
     int drawable_width, drawable_height;
+    SDL_Rect damage_region;
     SDL_bool needs_resize_event;
     SDL_bool floating_resize_pending;
 } SDL_WindowData;