some explenations

src/Affection.hs

@@ -67,25 +67,35 @@ withAffection AffectionConfig{..} = do
     }) =<< loadState surface
   (_, nState) <- runStateT ( A.runState $ do
     preLoop
+    liftIO $ SDL.surfaceBlit surface Nothing oldSurf Nothing
     whileM_ (do
         current <- get
         return $ not $ A.quitEvent current
       )
       (do
+        -- Measure time difference form last run
         now      <- liftIO $ getTime Monotonic
         lastTime <- liftIO $ fromMaybe now <$> tryReadMVar execTime
+        -- get state
         ad <- get
+        -- clean draw requests from last run
         mapM_ (invalidateDrawRequest pixels format stride cpp) $ drawStack ad
         put $ ad
           { drawStack = [] }
+        -- execute user defined draw loop
         drawLoop
+        -- execute user defined update loop
         updateLoop $ (fromIntegral $ toNanoSecs $ diffTimeSpec lastTime now) /
           (fromIntegral 10 ^ 9)
-        ad <- get
-        clear <- return . catMaybes =<< mapM (handleDrawRequest pixels format stride cpp) (drawStack ad)
+        -- handle all new draw requests
+        clear <- catMaybes <$> mapM (handleDrawRequest pixels format stride cpp) (drawStack ad)
+        -- save all draw requests to clear in next run
         put $ ad
           { drawStack = clear }
+        -- blit surface and update window
         liftIO $ SDL.surfaceBlit surface Nothing oldSurf Nothing
+        liftIO $ SDL.updateWindowSurface $ drawWindow ad
+        -- save new time
         _ <- liftIO $ swapMVar execTime $ now
         return ()
       )