implement FPS meter in Console output

src/Main.hs

@@ -11,9 +11,12 @@ import Control.Monad.Loops
 import Control.Monad.IO.Class
 import Control.Monad.Trans.Resource
 import Data.Bits
+import Data.ByteString.Char8
 import qualified Data.Map.Strict as M
+import Data.Time.Clock
 import qualified Data.Vector as V
 import qualified SDL hiding (V2)
+import System.IO (stdout)
 import System.Mem
 import qualified Vulkan as Vk
 import qualified Vulkan.Zero as Vk
@@ -44,6 +47,8 @@ main = do
 
     -- create abort condition for upcoming lop
     quit <- liftIO $ STM.newTMVarIO True
+    time <- liftIO $ STM.newTMVarIO =<< getCurrentTime
+    average <- liftIO $ STM.newTMVarIO 0
 
     -- main loop
     whileM_
@@ -51,11 +56,24 @@ main = do
         )
       ( do
         liftIO performMajorGC
+        now <- liftIO getCurrentTime
+        before <- liftIO $ STM.atomically $ STM.swapTMVar time now
+        let timeDiff = diffUTCTime now before
+            fps = recip $ nominalDiffTimeToSeconds timeDiff
+        liftIO $ hPutStr stdout $ pack $ "Current FPS: " <> show (floor fps) <> "  \r"
         number <- liftIO $ STM.atomically $ do
           number <- STM.readTMVar frameNumber
+          if number == 0 then
+            void $ STM.swapTMVar average fps
+          else do
+            oldAverage <- STM.readTMVar average
+            let newAverage = (oldAverage * fromIntegral number + fps) / frameCount
+                frameCount = fromIntegral number + 1
+            void $ STM.swapTMVar average newAverage
           void $ STM.swapTMVar frameNumber (succ number)
           return number
         -- draw
+        -- liftIO $ putStr $ show (recip $ nominalDiffTimeToSeconds timeDiff) <> "\r"
         drawFrame engineData number
         -- poll events
         evs <- liftIO SDL.pollEvents
@@ -69,6 +87,12 @@ main = do
           evs
       )
 
+    fps <- liftIO $ STM.atomically $ STM.readTMVar average
+
+    liftIO $ hPutStr stdout $
+      "\n" <>
+      "Average FPS: " <> pack (show fps) <> "\n"
+
     Vk.deviceWaitIdle $ engineLogicalDevice engineData
 
 createBufferView

vulkan-tutorial.cabal

@@ -50,6 +50,7 @@ executable vulkan-tutorial
                     , linear
                     , monad-loops
                     , stm
+                    , time
                     , bytestring
                     , text
                     , vector