Make convert format hold its own PixelFormat struct

I'm worried that if we use a reference to a pixelformat struct from a surface, the pixelformat might be deallocated later by SDL. This makes the code more complex but it ensures that the module always has a handle on a real and not-deallocated pixelformat.

Author: Starbuck5

src_c/base.c

@@ -2068,10 +2068,14 @@ pg_GetDefaultConvertFormat(void)
     return pg_default_convert_format;
 }
 
-static void
-pg_SetDefaultConvertFormat(SDL_PixelFormat *fmt)
+static SDL_PixelFormat *
+pg_SetDefaultConvertFormat(Uint32 format)
 {
-    pg_default_convert_format = fmt;
+    if (pg_default_convert_format != NULL) {
+        SDL_FreeFormat(pg_default_convert_format);
+    }
+    pg_default_convert_format = SDL_AllocFormat(format);
+    return pg_default_convert_format;  // returns for NULL error checking
 }
 
 static char *

src_c/include/_pygame.h

@@ -177,7 +177,7 @@ typedef struct pg_bufferinfo_s {
     (*(SDL_PixelFormat * (*)(void)) PYGAMEAPI_GET_SLOT(base, 27))
 
 #define pg_SetDefaultConvertFormat \
-    (*(void (*)(SDL_PixelFormat *))PYGAMEAPI_GET_SLOT(base, 28))
+    (*(SDL_PixelFormat * (*)(Uint32)) PYGAMEAPI_GET_SLOT(base, 28))
 
 #define import_pygame_base() IMPORT_PYGAME_MODULE(base)
 #endif /* ~PYGAMEAPI_BASE_INTERNAL */

src_c/window.c

@@ -164,8 +164,13 @@ window_get_surface(pgWindowObject *self)
     }
     self->surf->surf = _surf;
 
-    if (pg_GetDefaultConvertFormat() == NULL)
-        pg_SetDefaultConvertFormat(_surf->format);
+    if (pg_GetDefaultConvertFormat() == NULL) {
+        if (pg_SetDefaultConvertFormat(_surf->format->format) == NULL) {
+            /* This is very unlikely, I think only would happen if SDL runs
+             * out of memory when allocating the format. */
+            return RAISE(pgExc_SDLError, SDL_GetError());
+        }
+    }
 
     Py_INCREF(self->surf);
     return (PyObject *)self->surf;