Add goldenFormat2, add golden test for troublesome polygons

tests/GoldenSpec/Spec.hs

@@ -4,8 +4,9 @@
 
 module GoldenSpec.Spec (spec) where
 
-import GoldenSpec.Util (golden, goldenAllFormats)
+import GoldenSpec.Util (golden, goldenAllFormats, goldenFormat2)
 import Graphics.Implicit
+import Graphics.Implicit.Export.OutputFormat (OutputFormat (PNG))
 import Prelude
 import Test.Hspec ( describe, Spec )
 import Graphics.Implicit.Primitives (torus, ellipsoid, cone)
@@ -193,4 +194,27 @@ spec = describe "golden tests" $ do
       (C1 1)
       (Left 0)
       (union [circle 10])
-      $ Left 40
+      $ Left 40
+
+  -- These two should be equal, but internally when sampled at (V2 (-1) 0)
+  -- the sign of the SDF differs yet they both get rendered correctly.
+  let funPoly = polygon [V2 0 0, V2 0 (-0.1), V2 (-2) 0, V2 0 (-1)]
+      rotFunPoly = rotate (2*pi) funPoly
+  --
+  -- > getImplicit funPoly (V2 (-1) 0)
+  -- -4.993761694389224e-2
+  -- > getBox funPoly
+  -- (V2 (-2.0) (-1.0),V2 0.0 0.0)
+  --
+  -- vs
+  --
+  -- > getImplicit rotFunPoly (V2 (-1) 0))
+  -- 4.9937616943891996e-2
+  -- > getBox rotFunPoly
+  -- (V2 (-2.0000000000000004) (-1.0),V2 0.0 4.898587196589413e-16)
+  --
+  -- TODO(srk): investigate, see also #449
+
+  describe "2d" $ do
+    goldenFormat2 PNG "troublesome-polygon" 1 $ funPoly
+    goldenFormat2 PNG "troublesome-polygon-under-rotation" 1 $ rotFunPoly

tests/GoldenSpec/Util.hs

@@ -2,12 +2,12 @@
 {-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE LambdaCase   #-}
 
-module GoldenSpec.Util (golden, goldenAllFormats, goldenFormat) where
+module GoldenSpec.Util (golden, goldenAllFormats, goldenFormat, goldenFormat2) where
 
 import Control.Monad (forM_)
 import Control.Monad.IO.Class (liftIO)
-import Graphics.Implicit (SymbolicObj3)
-import Graphics.Implicit.Export (export3)
+import Graphics.Implicit (SymbolicObj2, SymbolicObj3)
+import Graphics.Implicit.Export (export2, export3)
 import Graphics.Implicit.Export.OutputFormat (OutputFormat (ASCIISTL), formats3D, formatExtension)
 import Prelude (IO, FilePath, Bool (True, False), String, Double, pure, (==), (>>=), (<>), ($), show)
 import System.Directory (getTemporaryDirectory, doesFileExist)
@@ -57,6 +57,36 @@ goldenFormat fmt name resolution sym = it (name <> " (golden, format: " <> show
     then pure ()
     else False `shouldBe` True
 
+-- | Construct a golden test for rendering the given 'SymbolicObj2' at the
+-- specified resolution. On the first run of this test, it will render the
+-- object and cache the results. Subsequent test runs will compare their result
+-- to the cached one. This is valuable for ensuring mesh generation doesn't
+-- break across commits.
+--
+-- The objects are cached under @tests/golden/@, with the given name. Deleting
+-- this file is sufficient to update the test if changes in the mesh generation
+-- are intended.
+-- TODO(srk): polymorphic export would be nice, related to #446
+goldenFormat2 :: OutputFormat -> String -> Double -> SymbolicObj2 -> SpecWith ()
+goldenFormat2 fmt name resolution sym = it (name <> " (golden, format: " <> show fmt <> ")") $ do
+  (res, cached) <- liftIO $ do
+    temp_fp <- getTemporaryFilePath "golden"
+    -- Output the rendered mesh
+    export2 fmt resolution temp_fp sym
+    !res <- readFile temp_fp
+    let golden_fp = "./tests/golden/" <> name <> "." <> formatExtension fmt
+    -- Check if the cached results already exist.
+    doesFileExist golden_fp >>= \case
+      True  -> pure ()
+      -- If not, save the mesh we just created in the cache.
+      False -> writeFile golden_fp res
+    !cached <- readFile golden_fp
+    pure (res, cached)
+  -- Finally, ceck if the two meshes are equal.
+  if res == cached
+    then pure ()
+    else False `shouldBe` True
+
 ------------------------------------------------------------------------------
 -- | Get a temporary filepath with the desired extension. On unix systems, this
 -- is a file under @/tmp@. Useful for tests that need to write files.