From fb18cce4ec89cb9701111f1d801d435bf6aab265 Mon Sep 17 00:00:00 2001
From: Kiana Sheibani <kiana.a.sheibani@gmail.com>
Date: Wed, 30 Nov 2022 14:52:35 -0500
Subject: [PATCH] Refactor code that was causing massive slowdown

I don't know why I thought it was a good idea to use `concat`,
but I'm not making that mistake again.
---
 src/Render/Scene.idr | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/src/Render/Scene.idr b/src/Render/Scene.idr
index eaaaa5b..4794412 100644
--- a/src/Render/Scene.idr
+++ b/src/Render/Scene.idr
@@ -2,6 +2,7 @@ module Render.Scene
 
 import Data.DPair
 import Data.Vect
+import Data.IORef
 import Data.Buffer
 import System.File
 import Render.Color
@@ -44,10 +45,14 @@ renderToPPM dest cam sc = do
     | Nothing => pure $ Right ()
 
   let pic = render cam sc
-  for_ (zip (tabulate fst) (concat pic)) $ \(i,[r,g,b]) => do
-        setByte buf (cast i * 3)     (cast $ r * 255)
-        setByte buf (cast i * 3 + 1) (cast $ g * 255)
-        setByte buf (cast i * 3 + 2) (cast $ b * 255)
+  ind <- newIORef 0
+  for_ pic $ traverse_ $ \[r,g,b] => do
+        i <- readIORef ind
+        setByte buf (i)     (cast $ r * 255)
+        setByte buf (i + 1) (cast $ g * 255)
+        setByte buf (i + 2) (cast $ b * 255)
+        modifyIORef ind (+3)
+
 
   _ <- if !(exists dest) then removeFile {io} dest else pure $ Right ()
   Right h <- openFile dest Append