Partial rendering of maps through viewports works now (this allows us to scroll the map under a camera)

src/sdl3-gametest.c

@@ -128,7 +128,7 @@ SDL_AppResult SDL_AppEvent(void *appstate, SDL_Event *event)
 SDL_AppResult SDL_AppIterate(void *appstate)
 {
   SDL_FRect dest;
-  SDL_FRect viewport = {.x = 0, .y = 0, .w = 640, .h = 480};
+  SDL_FRect viewport = {.x = 50, .y = 50, .w = 640, .h = 480};
   b2Vec2 position;
   
   actor_update(&player);