From 07cde953417fff5dc1886809231657061f712eab Mon Sep 17 00:00:00 2001
From: Rostyslav Hnatyshyn <rostyslav.hnatyshyn@gmail.com>
Date: Sat, 24 Sep 2022 18:58:08 -0700
Subject: [PATCH] added antialiasing, fixed x-y issue

---
 app/Main.hs | 27 +++++++++++++++------------
 src/Ray.hs  |  8 ++++----
 2 files changed, 19 insertions(+), 16 deletions(-)

diff --git a/app/Main.hs b/app/Main.hs
index 17a2feb..12474fc 100644
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -17,9 +17,6 @@ type Coord = (Int, Int)
 
 type ImageDimensions = (Int, Int)
 
--- TODO
--- antialiasing
-
 -- scatter rays based on the material of the object that was hit
 scatter :: (RandomGen g) => Ray -> Hit -> Rand g (Ray)
 scatter (Ray o d) (Hit t p n (Lambertian c)) = do
@@ -44,6 +41,16 @@ scatter (Ray o d) (Hit t p n (Glass c)) = do
       let refracted = refract ud n refraction_ratio
       return $ Ray p refracted
 
+grc :: (RandomGen g, Shape s) => (Int, Int) -> ImageDimensions -> [s] -> Int -> Camera -> Rand g (V3 Double)
+grc (x, y) (w, h) ws d camera = do
+  ray <- buildRayAA xf yf wf hf camera
+  getRayColor ws d ray
+  where
+    xf = fromIntegral x
+    yf = fromIntegral y
+    wf = fromIntegral (w - 1)
+    hf = fromIntegral (h - 1)
+
 getRayColor :: (Shape s, RandomGen g) => [s] -> Int -> Ray -> Rand g (V3 Double)
 getRayColor ws d r = do
   let h = getBestHit (mapMaybe (testHit r) ws)
@@ -83,15 +90,10 @@ colorWithNormal v = 0.5 *^ (v ^+^ V3 1.0 1.0 1.0)
 -- heart of loop, for each x y coordinate pixel, convert it into world space and then run the ray tracing algorithm
 -- run [samples] times in order to increase fidelity
 rayTrace :: (Shape s) => (Int, Int) -> ImageDimensions -> [s] -> Int -> Camera -> IO (V3 Double)
-rayTrace (x, y) (w, h) world samples camera = do
+rayTrace coord dim world samples camera = do
   let maxDepth = 50
-  l <- replicateM samples (evalRandIO (getRayColor world maxDepth $ buildRay (xf / wf) (yf / hf) camera))
+  l <- replicateM samples (evalRandIO (grc coord dim world maxDepth camera))
   return $ foldl (^+^) (V3 0.0 0.0 0.0) l
-  where
-    xf = fromIntegral x
-    yf = fromIntegral y
-    wf = fromIntegral (w - 1)
-    hf = fromIntegral (h - 1)
 
 main :: IO ()
 main = do
@@ -108,10 +110,11 @@ main = do
   let samples = 25
   let world =
         [ Circle (V3 0.0 0.0 (-1.0)) 0.5 (Glass (V3 1.0 1.0 1.0)),
-          Circle (V3 1.0 0.0 (-1.0)) 0.5 (Lambertian (V3 0.7 0.1 0.1)),
+          Circle (V3 1.0 0.0 (-1.0)) 0.5 (Lambertian (V3 1.0 0.753 0.796)),
           Circle (V3 0.0 (-100.5) (-1.0)) 100 (Lambertian (V3 0.7 0.6 0.5))
         ]
-  let coords = [(x, y) | x <- reverse [0 .. w - 1], y <- [0 .. h - 1]]
+  -- y x because most raytracing algorithms go top to bottom, left to right
+  let coords = [(y, x) | x <- reverse [0 .. w - 1], y <- [0 .. h - 1]]
   colors <- mapM (\x -> rayTrace x (w, h) world samples camera) coords
   let convertedColors = map v3ToColor colors
   -- print ppm header
diff --git a/src/Ray.hs b/src/Ray.hs
index 334c425..28ed401 100644
--- a/src/Ray.hs
+++ b/src/Ray.hs
@@ -23,11 +23,11 @@ rayAt (Ray origin dir) t = origin + (t *^ dir)
 calculateRayNormal :: Ray -> Double -> V3 Double
 calculateRayNormal r t = unitVector (rayAt r t ^-^ V3 0.0 0.0 1.0)
 
-buildRayAA :: (RandomGen g) => Double -> Double -> Camera -> Rand g Ray
-buildRayAA u v camera = do
+buildRayAA :: (RandomGen g) => Double -> Double -> Double -> Double -> Camera -> Rand g Ray
+buildRayAA u v w h camera = do
   ur <- rand
   vr <- rand
-  return $ buildRay (u + ur) (v + vr) camera
+  return $ buildRay ((u + ur) / w) ((v + vr) / h) camera
 
 buildRay :: Double -> Double -> Camera -> Ray
-buildRay u v (Camera o ll h vv) = Ray o (ll ^+^ (v *^ h) ^+^ (u *^ vv) ^-^ o)
+buildRay u v (Camera o ll h vv) = Ray o (ll ^+^ (u *^ h) ^+^ (v *^ vv) ^-^ o)