display.c: fix scaled-after-non-scaled usage

Author: ankith26

src_c/display.c

@@ -824,6 +824,64 @@ _get_display(SDL_Window *win)
     }
     return display;
 }
+#if SDL_VERSION_ATLEAST(2, 28, 0)
+void
+PG_DestroyWindowSurface(SDL_Window *win)
+{
+    if (SDL_HasWindowSurface(win)) {
+        SDL_DestroyWindowSurface(win);
+    }
+}
+#else
+/* SDL_Window struct, as taken from the SDL source (except some pointer types
+ * have been replaced with `void *`) */
+struct SDL_Window {
+    const void *magic;
+    Uint32 id;
+    char *title;
+    int x, y;
+    int w, h;
+    int min_w, min_h;
+    int max_w, max_h;
+    Uint32 flags;
+
+    /* Stored position and size for windowed mode */
+    SDL_Rect windowed;
+
+    SDL_DisplayMode fullscreen_mode;
+
+    float brightness;
+    Uint16 *gamma;
+    Uint16 *saved_gamma; /* (just offset into gamma) */
+
+    SDL_Surface *surface;
+    SDL_bool surface_valid;
+
+    void *shaper;
+
+    void *data;
+
+    void *driverdata;
+
+    SDL_Window *prev;
+    SDL_Window *next;
+};
+
+void
+PG_DestroyWindowSurface(SDL_Window *win)
+{
+    /* This is logic taken from the implementation of SDL_DestroyWindowSurface
+     * in the versions before it was added. We can safely do this because
+     * SDL 2.x has been ABI compatible between releases, and the same destroy
+     * surface logic was internally used all the way back till SDL 2.0.10 */
+    if (win->surface) {
+        win->surface->flags &= ~SDL_DONTFREE;
+        SDL_FreeSurface(win->surface);
+        win->surface = NULL;
+        win->surface_valid = SDL_FALSE;
+    }
+}
+#endif
 
 static PyObject *
 pg_set_mode(PyObject *self, PyObject *arg, PyObject *kwds)
@@ -1215,6 +1273,11 @@ pg_set_mode(PyObject *self, PyObject *arg, PyObject *kwds)
                     SDL_SetHintWithPriority(SDL_HINT_RENDER_SCALE_QUALITY,
                                             "nearest", SDL_HINT_DEFAULT);
 
+                    /* If the window has a surface associated with it already,
+                     * we need to destroy it (if possible) because now we are
+                     * associating a renderer with it. */
+                    PG_DestroyWindowSurface(win);
+
                     if (vsync) {
                         pg_renderer = SDL_CreateRenderer(
                             win, -1, SDL_RENDERER_PRESENTVSYNC);