fix brush stroke point order for open brush path

* also: add some preset brushes

MetaBrush.cabal

@@ -98,7 +98,8 @@ executable MetaBrush
         Main.hs
 
     other-modules:
-        MetaBrush.Asset.Colours
+        MetaBrush.Asset.Brushes
+      , MetaBrush.Asset.Colours
       , MetaBrush.Asset.Cursor
       , MetaBrush.Asset.InfoBar
       , MetaBrush.Asset.Logo

app/Main.hs

@@ -58,6 +58,8 @@ import Math.Bezier.Stroke
   ( StrokePoint(..) )
 import Math.Vector2D
   ( Point2D(..) )
+import MetaBrush.Asset.Brushes
+  ( ellipse, rect )
 import MetaBrush.Asset.Colours
   ( getColours )
 import MetaBrush.Asset.Logo
@@ -102,7 +104,7 @@ testDocuments = IntMap.fromList
       { displayName    = "Document 1"
       , filePath       = Nothing
       , unsavedChanges = False
-      , strokes        = [ Stroke ( circle ( PointData Normal ( rect $ BrushPointData Normal ) ) ) "Circle" True ( unsafeUnique 0 )
+      , strokes        = [ Stroke ( ellipse 150 100 ( PointData Normal ( rect 30 6 $ BrushPointData Normal ) ) ) "Ellipse" True ( unsafeUnique 0 )
                          ]
       , bounds         = AABB ( Point2D 0 0 ) ( Point2D 100 100 )
       , viewportCenter = Point2D 50 50
@@ -112,62 +114,20 @@ testDocuments = IntMap.fromList
       { displayName    = "Document 2"
       , filePath       = Nothing
       , unsavedChanges = True
-      , strokes        = [ ]
+      , strokes        = [ Stroke linePts "Line" True ( unsafeUnique 1 ) ]
       , bounds         = AABB ( Point2D  0  0 ) ( Point2D 50 50 )
-      , viewportCenter = Point2D 10 10
+      , viewportCenter = Point2D 0 0
-      , zoomFactor     = 0.25
+      , zoomFactor     = 1
       }
     ]
-
-circle :: forall a. a -> Seq ( StrokePoint a )
-circle d = Seq.fromList
-  [ pp ( Point2D   0    1  )
-  , cp ( Point2D   a    1  )
-  , cp ( Point2D   1    a  )
-  , pp ( Point2D   1    0  )
-  , cp ( Point2D   1  (-a) )
-  , cp ( Point2D   a  (-1) )
-  , pp ( Point2D   0  (-1) )
-  , cp ( Point2D (-a) (-1) )
-  , cp ( Point2D (-1) (-a) )
-  , pp ( Point2D (-1)   0  )
-  , cp ( Point2D (-1)   a  )
-  , cp ( Point2D (-a)   1  )
-  , pp ( Point2D   0    1  )
-  ]
   where
-    a :: Double
+    linePts :: Seq ( StrokePoint PointData )
-    a = 0.551915024494
+    linePts = Seq.fromList
-    pp, cp :: Point2D Double -> StrokePoint a
+      [    PathPoint ( Point2D 0 (-100) ) ( PointData Normal ( ellipse 30 8 $ BrushPointData Normal ) )
-    pp p =    PathPoint ( fmap ( * 100 ) p ) d
+      , ControlPoint ( Point2D 0 ( -30) ) ( PointData Normal ( ellipse 25 6 $ BrushPointData Normal ) )
-    cp p = ControlPoint ( fmap ( * 100 ) p ) d
+      , ControlPoint ( Point2D 0 (  30) ) ( PointData Normal ( ellipse 15 6 $ BrushPointData Normal ) )
-
+      ,    PathPoint ( Point2D 0 ( 100) ) ( PointData Normal ( ellipse  5 2 $ BrushPointData Normal ) )
-razor :: forall a. a -> Seq ( StrokePoint a )
+      ]
-razor d = Seq.fromList
-  [ pp ( Point2D  30  0 )
-  , cp ( Point2D  30 -6 )
-  , cp ( Point2D -30 -6 )
-  , pp ( Point2D -30  0 )
-  , cp ( Point2D -30  3 )
-  , cp ( Point2D  30  3 )
-  , pp ( Point2D  30  0 )
-  ]
-  where
-    pp, cp :: Point2D Double -> StrokePoint a
-    pp p =    PathPoint p d
-    cp p = ControlPoint p d
-
-rect :: forall a. a -> Seq ( StrokePoint a )
-rect d = Seq.fromList
-  [ pp ( Point2D  20   5 )
-  , pp ( Point2D  20  -5 )
-  , pp ( Point2D -20  -5 )
-  , pp ( Point2D -20   5 )
-  , pp ( Point2D  20   5 )
-  ]
-  where
-    pp :: Point2D Double -> StrokePoint a
-    pp p = PathPoint p d
 
 --------------------------------------------------------------------------------
 

src/app/MetaBrush/Asset/Brushes.hs

@@ -0,0 +1,70 @@
+{-# LANGUAGE NegativeLiterals    #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+
+module MetaBrush.Asset.Brushes
+  ( ellipse, blob, rect )
+  where
+
+-- containers
+import Data.Sequence
+  ( Seq(..) )
+import qualified Data.Sequence as Seq
+  ( fromList )
+
+-- MetaBrush
+import Math.Bezier.Stroke
+  ( StrokePoint(..) )
+import Math.Vector2D
+  ( Point2D(..) )
+
+--------------------------------------------------------------------------------
+
+ellipse :: forall d. Double -> Double -> d -> Seq ( StrokePoint d )
+ellipse w h d = Seq.fromList
+  [ pp ( Point2D   0    1  )
+  , cp ( Point2D   a    1  )
+  , cp ( Point2D   1    a  )
+  , pp ( Point2D   1    0  )
+  , cp ( Point2D   1  (-a) )
+  , cp ( Point2D   a  (-1) )
+  , pp ( Point2D   0  (-1) )
+  , cp ( Point2D (-a) (-1) )
+  , cp ( Point2D (-1) (-a) )
+  , pp ( Point2D (-1)   0  )
+  , cp ( Point2D (-1)   a  )
+  , cp ( Point2D (-a)   1  )
+  , pp ( Point2D   0    1  )
+  ]
+  where
+    a :: Double
+    a = 0.551915024494
+    pp, cp :: Point2D Double -> StrokePoint d
+    pp ( Point2D x y ) =    PathPoint ( Point2D ( w * x ) ( h * y ) ) d
+    cp ( Point2D x y ) = ControlPoint ( Point2D ( w * x ) ( h * y ) ) d
+
+blob :: forall d. Double -> Double -> d -> Seq ( StrokePoint d )
+blob w h d = Seq.fromList
+  [ pp ( Point2D  1  0 )
+  , cp ( Point2D  1 -1 )
+  , cp ( Point2D -1 -1 )
+  , pp ( Point2D -1  0 )
+  , cp ( Point2D -1  1 )
+  , cp ( Point2D  1  1 )
+  , pp ( Point2D  1  0 )
+  ]
+  where
+    pp, cp :: Point2D Double -> StrokePoint d
+    pp ( Point2D x y ) =    PathPoint ( Point2D ( w * x ) ( h * y ) ) d
+    cp ( Point2D x y ) = ControlPoint ( Point2D ( w * x ) ( h * y ) ) d
+
+rect :: forall d. Double -> Double -> d -> Seq ( StrokePoint d )
+rect w h d = Seq.fromList
+  [ pp ( Point2D  1  1 )
+  , pp ( Point2D  1 -1 )
+  , pp ( Point2D -1 -1 )
+  , pp ( Point2D -1  1 )
+  , pp ( Point2D  1  1 )
+  ]
+  where
+    pp :: Point2D Double -> StrokePoint d
+    pp ( Point2D x y ) = PathPoint ( Point2D ( w * x ) ( h * y ) ) d

src/lib/Math/Bezier/Stroke.hs

@@ -115,18 +115,17 @@ stroke allPts@( spt0 :<| spt1 :<| spts )
   | isClosed
   = Right ( fwdPts, bwdPts )
   | otherwise
-  = Left ( fwdPts <> bwdPts )
+  = Left ( startingCap <> fwdPts <> bwdPts )
   where
 
     startOffset, endOffset :: Vector2D Double
     tgt_start, tgt_end :: Vector2D Double
+    brush_start, brush_end :: Seq ( StrokePoint x )
     startOffset = Point2D 0 0 --> coords spt0
     tgt_start = coords spt0 --> coords spt1
-    ( tgt_end, endOffset ) = case allPts of
+    ( tgt_end, endOffset, brush_end ) = case allPts of
-      _ :|> sptnm1 :|> sptn -> ( coords sptnm1 --> coords sptn, Point2D 0 0 --> coords sptn )
+      _ :|> sptnm1 :|> sptn -> ( coords sptnm1 --> coords sptn, Point2D 0 0 --> coords sptn, brushShape sptn )
       _                     -> error "impossible"
-
-    brush_start :: Seq ( StrokePoint x )
     brush_start = brushShape spt0
 
     isClosed :: Bool
@@ -149,19 +148,6 @@ stroke allPts@( spt0 :<| spt1 :<| spts )
     -- Connecting paths at a point of discontinuity of the tangent vector direction (G1 discontinuity).
     -- This happens at corners of the brush path (including endpoints of an open brush path, where the tangent flips direction).
     joinAndContinue :: Vector2D Double -> StrokePoint d -> Seq ( StrokePoint d ) -> ( Seq ( StrokePoint () ), Seq ( StrokePoint () ) )
-    joinAndContinue _ _ Empty
-      -- Closed curve.
-      | isClosed
-      = if parallel tgt_start tgt_end
-        then ( Empty, Empty )
-        else ( startOffset • joinWithBrush  ( withTangent           tgt_start   brush_start ) ( withTangent           tgt_end   brush_start ) brush_start
-             , startOffset • joinWithBrush  ( withTangent ( (-1) *^ tgt_start ) brush_start ) ( withTangent ( (-1) *^ tgt_end ) brush_start ) brush_start
-             )
-      -- Open curve.
-      | otherwise
-      = ( endOffset   • joinWithBrush ( withTangent           tgt_end     brush_start ) ( withTangent ( (-1) *^ tgt_end ) brush_start ) brush_start
-        , startOffset • joinWithBrush ( withTangent ( (-1) *^ tgt_start ) brush_start ) ( withTangent           tgt_start brush_start ) brush_start
-        )
     joinAndContinue tgt sp0 ( sp1 :<| sps )
       | tgt' `parallel` tgt
       = go sp0 ( sp1 :<| sps )
@@ -177,6 +163,24 @@ stroke allPts@( spt0 :<| spt1 :<| spts )
         tgt' = coords sp0 --> coords sp1
         brush0 :: Seq ( StrokePoint () )
         brush0 = removePointData $ brushShape @x sp0
+    joinAndContinue _ _ Empty
+      -- Closed curve.
+      | isClosed
+      = if parallel tgt_start tgt_end
+        then ( Empty, Empty )
+        else ( startOffset • joinWithBrush  ( withTangent           tgt_start   brush_start ) ( withTangent           tgt_end   brush_start ) brush_start
+             , startOffset • joinWithBrush  ( withTangent ( (-1) *^ tgt_start ) brush_start ) ( withTangent ( (-1) *^ tgt_end ) brush_start ) brush_start
+             )
+      -- Open curve.
+      | otherwise
+      = ( endOffset   • joinWithBrush ( withTangent           tgt_end     brush_end   ) ( withTangent ( (-1) *^ tgt_end ) brush_end   ) brush_end
+        , Empty -- handled separately: see 'startingCap' below
+        )
+
+    -- Final cap for an open curve. Handled separately for correct stroke order.
+    startingCap :: Seq ( StrokePoint () ) 
+    startingCap
+      =   startOffset • joinWithBrush ( withTangent ( (-1) *^ tgt_start ) brush_start ) ( withTangent           tgt_start brush_start ) brush_start
 
     go :: StrokePoint d -> Seq ( StrokePoint d ) -> ( Seq ( StrokePoint () ), Seq ( StrokePoint () ) )
     go _ Empty = ( Empty, Empty )