video: Try to reconfigure the window for OpenGL without destroying it

When attaching a renderer (GL based specifically) to a window that was not created with the appropriate flags, the window would be destroyed and recreated to configure it for the desired rendering backend. While most of the issues with this have been mitigated over time, there can still be some undesirable side effects from doing so on certain platforms.

If the window was just created and was never configured for any graphics context, it is possible that the reconfiguration can be done without destroying the window first.

The Wayland implementation fixes an issue when creating a window with the fullscreen flag on wlroots based Wayland compositors, and can likely be extended to other platforms to avoid unnecessarily destroying/recreating a window in the very common case where a window is created, followed immediately by attaching a renderer.

src/render/opengl/SDL_render_gl.c

@@ -1666,7 +1666,7 @@ static bool GL_CreateRenderer(SDL_Renderer *renderer, SDL_Window *window, SDL_Pr
         SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, RENDERER_CONTEXT_MAJOR);
         SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, RENDERER_CONTEXT_MINOR);
 
-        if (!SDL_RecreateWindow(window, (window_flags & ~(SDL_WINDOW_VULKAN | SDL_WINDOW_METAL)) | SDL_WINDOW_OPENGL)) {
+        if (!SDL_ReconfigureWindow(window, (window_flags & ~(SDL_WINDOW_VULKAN | SDL_WINDOW_METAL)) | SDL_WINDOW_OPENGL)) {
             goto error;
         }
     }

src/render/opengles2/SDL_render_gles2.c

@@ -2176,7 +2176,7 @@ static bool GLES2_CreateRenderer(SDL_Renderer *renderer, SDL_Window *window, SDL
         SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, RENDERER_CONTEXT_MAJOR);
         SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, RENDERER_CONTEXT_MINOR);
 
-        if (!SDL_RecreateWindow(window, (window_flags & ~(SDL_WINDOW_VULKAN | SDL_WINDOW_METAL)) | SDL_WINDOW_OPENGL)) {
+        if (!SDL_ReconfigureWindow(window, (window_flags & ~(SDL_WINDOW_VULKAN | SDL_WINDOW_METAL)) | SDL_WINDOW_OPENGL)) {
             goto error;
         }
     }

src/video/SDL_sysvideo.h

@@ -314,6 +314,7 @@ struct SDL_VideoDevice
     bool (*ApplyWindowProgress)(SDL_VideoDevice *_this, SDL_Window *window);
     bool (*SetWindowFocusable)(SDL_VideoDevice *_this, SDL_Window *window, bool focusable);
     bool (*SyncWindow)(SDL_VideoDevice *_this, SDL_Window *window);
+    bool (*ReconfigureWindow)(SDL_VideoDevice *_this, SDL_Window *window, SDL_WindowFlags flags);
 
     /* * * */
     /*
@@ -574,6 +575,7 @@ extern void SDL_SetWindowSafeAreaInsets(SDL_Window *window, int left, int right,
 extern void SDL_GL_DeduceMaxSupportedESProfile(int *major, int *minor);
 
 extern bool SDL_RecreateWindow(SDL_Window *window, SDL_WindowFlags flags);
+extern bool SDL_ReconfigureWindow(SDL_Window *window, SDL_WindowFlags flags);
 extern bool SDL_HasWindows(void);
 extern void SDL_RelativeToGlobalForWindow(SDL_Window *window, int rel_x, int rel_y, int *abs_x, int *abs_y);
 extern void SDL_GlobalToRelativeForWindow(SDL_Window *window, int abs_x, int abs_y, int *rel_x, int *rel_y);

src/video/SDL_video.c

@@ -2634,6 +2634,66 @@ SDL_Window *SDL_CreatePopupWindow(SDL_Window *parent, int offset_x, int offset_y
     return window;
 }
 
+static bool SDL_ReconfigureWindowInternal(SDL_Window *window, SDL_WindowFlags flags)
+{
+    bool loaded_opengl = false;
+    bool loaded_vulkan = false;
+
+    if (!_this->ReconfigureWindow) {
+        return false;
+    }
+
+    // Only attempt to reconfigure if the window has no existing graphics flags.
+    if (window->flags & (SDL_WINDOW_OPENGL | SDL_WINDOW_METAL | SDL_WINDOW_VULKAN)) {
+        return false;
+    }
+
+    const SDL_WindowFlags graphics_flags = flags & (SDL_WINDOW_OPENGL | SDL_WINDOW_METAL | SDL_WINDOW_VULKAN);
+    if (graphics_flags & (graphics_flags - 1)) {
+        return SDL_SetError("Conflicting window flags specified");
+    }
+
+    if ((flags & SDL_WINDOW_OPENGL) && !_this->GL_CreateContext) {
+        return SDL_ContextNotSupported("OpenGL");
+    }
+    if ((flags & SDL_WINDOW_VULKAN) && !_this->Vulkan_CreateSurface) {
+        return SDL_ContextNotSupported("Vulkan");
+    }
+    if ((flags & SDL_WINDOW_METAL) && !_this->Metal_CreateView) {
+        return SDL_ContextNotSupported("Metal");
+    }
+
+    SDL_DestroyWindowSurface(window);
+
+    if (graphics_flags & SDL_WINDOW_OPENGL) {
+        loaded_opengl = SDL_GL_LoadLibrary(NULL);
+        if (!loaded_opengl) {
+            return false;
+        }
+    } else if (graphics_flags & SDL_WINDOW_VULKAN) {
+        loaded_vulkan = SDL_GL_LoadLibrary(NULL);
+        if (!loaded_vulkan) {
+            return false;
+        }
+    }
+
+    // Try to reconfigure the window for the requested graphics flags.
+    if (!_this->ReconfigureWindow(_this, window, graphics_flags)) {
+        if (loaded_opengl) {
+            SDL_GL_UnloadLibrary();
+        }
+        if (loaded_vulkan) {
+            SDL_Vulkan_UnloadLibrary();
+        }
+
+        return false;
+    }
+
+    window->flags |= graphics_flags;
+
+    return true;
+}
+
 bool SDL_RecreateWindow(SDL_Window *window, SDL_WindowFlags flags)
 {
     bool loaded_opengl = false;
@@ -2788,6 +2848,16 @@ bool SDL_RecreateWindow(SDL_Window *window, SDL_WindowFlags flags)
     return true;
 }
 
+bool SDL_ReconfigureWindow(SDL_Window *window, SDL_WindowFlags flags)
+{
+    // Try to reconfigure the window for the desired flags first, before completely destroying and recreating it.
+    if (!SDL_ReconfigureWindowInternal(window, flags)) {
+        return SDL_RecreateWindow(window, flags);
+    }
+
+    return true;
+}
+
 bool SDL_HasWindows(void)
 {
     return _this && _this->windows;

src/video/wayland/SDL_waylandvideo.c

@@ -660,6 +660,7 @@ static SDL_VideoDevice *Wayland_CreateDevice(bool require_preferred_protocols)
     device->ShowWindowSystemMenu = Wayland_ShowWindowSystemMenu;
     device->SyncWindow = Wayland_SyncWindow;
     device->SetWindowFocusable = Wayland_SetWindowFocusable;
+    device->ReconfigureWindow = Wayland_ReconfigureWindow;
 
 #ifdef SDL_USE_LIBDBUS
     if (SDL_SystemTheme_Init())

src/video/wayland/SDL_waylandwindow.c

@@ -2543,6 +2543,49 @@ bool Wayland_SetWindowKeyboardGrab(SDL_VideoDevice *_this, SDL_Window *window, b
     return true;
 }
 
+bool Wayland_ReconfigureWindow(SDL_VideoDevice *_this, SDL_Window *window, SDL_WindowFlags flags)
+{
+    SDL_WindowData *data = window->internal;
+
+    if (data->shell_surface_status == WAYLAND_SHELL_SURFACE_STATUS_SHOWN) {
+        // Window is already mapped; abort.
+        return false;
+    }
+
+    /* The caller guarantees that only one of the GL or Vulkan flags will be set,
+     * and the window will have no previous video flags.
+     */
+    if (flags & SDL_WINDOW_OPENGL) {
+        if (!data->egl_window) {
+            data->egl_window = WAYLAND_wl_egl_window_create(data->surface, data->current.pixel_width, data->current.pixel_height);
+        }
+
+#ifdef SDL_VIDEO_OPENGL_EGL
+        // Create the GLES window surface
+        data->egl_surface = SDL_EGL_CreateSurface(_this, window, (NativeWindowType)data->egl_window);
+
+        if (data->egl_surface == EGL_NO_SURFACE) {
+            return false; // SDL_EGL_CreateSurface should have set error
+        }
+#endif
+
+        if (!data->gles_swap_frame_event_queue) {
+            data->gles_swap_frame_event_queue = WAYLAND_wl_display_create_queue(data->waylandData->display);
+            data->gles_swap_frame_surface_wrapper = WAYLAND_wl_proxy_create_wrapper(data->surface);
+            WAYLAND_wl_proxy_set_queue((struct wl_proxy *)data->gles_swap_frame_surface_wrapper, data->gles_swap_frame_event_queue);
+            data->gles_swap_frame_callback = wl_surface_frame(data->gles_swap_frame_surface_wrapper);
+            wl_callback_add_listener(data->gles_swap_frame_callback, &gles_swap_frame_listener, data);
+        }
+
+        return true;
+    } else if (flags & SDL_WINDOW_VULKAN) {
+        // Nothing to configure for Vulkan.
+        return true;
+    }
+
+    return false;
+}
+
 bool Wayland_CreateWindow(SDL_VideoDevice *_this, SDL_Window *window, SDL_PropertiesID create_props)
 {
     SDL_WindowData *data;

src/video/wayland/SDL_waylandwindow.h

@@ -253,6 +253,7 @@ extern void *Wayland_GetWindowICCProfile(SDL_VideoDevice *_this, SDL_Window *win
 extern bool Wayland_SetWindowHitTest(SDL_Window *window, bool enabled);
 extern bool Wayland_FlashWindow(SDL_VideoDevice *_this, SDL_Window *window, SDL_FlashOperation operation);
 extern bool Wayland_SyncWindow(SDL_VideoDevice *_this, SDL_Window *window);
+extern bool Wayland_ReconfigureWindow(SDL_VideoDevice *_this, SDL_Window *window, SDL_WindowFlags flags);
 
 extern void Wayland_RemoveOutputFromWindow(SDL_WindowData *window, SDL_DisplayData *display_data);