From 5abe70c7457ebedc5e4e348e3dc5a7b830fab897 Mon Sep 17 00:00:00 2001
From: Joe Crayne <joe@jerkface.net>
Date: Thu, 2 May 2019 03:24:53 -0400
Subject: Rotate camera-up direction too.

---
 MeshSketch.hs | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/MeshSketch.hs b/MeshSketch.hs
index c88da0c..5bf6fea 100644
--- a/MeshSketch.hs
+++ b/MeshSketch.hs
@@ -170,7 +170,7 @@ whirlingCamera st = Animation $ \_ t -> do
     let tf = realToFrac t :: Float
         rot = rotMatrixZ (-tf/2) <> rotMatrixX (-tf/pi)
     modifyIORef (stCamera st) $ \cam -> cam
-                            { camUp            = rot #> fromList [0,1,0]
+                            { camUp            = fromList [0,1,0] <# rot
                             , camDirection     = (scale (1/camDistance cam) $ fromList [-2,-2,-10]) <# rot
                             , camWorldToScreen = Nothing
                             , camScreenToWorld = Nothing
@@ -335,9 +335,15 @@ updateCameraRotation w st h k = do
             -- tu = dt `dot` û
             -- td = dt `dot` d̂
             cosθ = dot df dt / realToFrac (norm_2 df) / realToFrac (norm_2 dt)
-            axis = df `cross` dt
+            axis0 = df `cross` dt
+            small x = abs x < 0.00001
+            axis = let xs = toList axis0
+                    in if any isNaN xs || all small xs
+                        then fromList [0,1,0]
+                        else axis0
             cam' = cam
                     { camDirection     = d̂ <# rotate cosθ axis
+                    , camUp            = û <# rotate cosθ axis
                     , camWorldToScreen = Nothing
                     , camScreenToWorld = Nothing
                     }
@@ -349,13 +355,20 @@ updateCameraRotation w st h k = do
 sanitizeCamera st = do
     modifyIORef (stCamera st) $ \cam ->
         let d = camDirection cam
+            u = camUp cam
             dd = norm_2 d
+            uu = norm_2 u
             e = scale (realToFrac $ 1/dd) d
             d̂ = if any isNaN (toList e)
                     then fromList [0,0,-1]
                     else e
+            f = scale (realToFrac $ 1/uu) u
+            û = if any isNaN (toList f)
+                    then fromList [0,1,0]
+                    else f
         in cam
             { camDirection = d̂
+            , camUp        = û
             , camWorldToScreen = Nothing
             , camScreenToWorld = Nothing
             }
-- 
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