Add layered drawing of pictures

src/Picture.hs

@@ -40,6 +40,7 @@ module Picture
     , mixColors
     , zeroZ
     , setDepth
+    , setLayer
     )
     where
 import Geometry
@@ -69,11 +70,11 @@ black = (0,0,0,1)
 
 polygon :: [Point2] -> Picture
 {-# INLINE polygon #-}
-polygon = Polygon
+polygon = Polygon 0
 
 polygonCol :: [(Point2,RGBA)] -> Picture
 {-# INLINE polygonCol #-}
-polygonCol = PolygonCol
+polygonCol = PolygonCol 0
 
 --polygon :: [Point2] -> Picture
 --{-# INLINE polygon #-}
@@ -101,6 +102,21 @@ setDepth :: Float -> Picture -> Picture
 {-# INLINE setDepth #-}
 setDepth d pic = SetDepth d pic
 
+setLayer :: Int -> Picture -> Picture
+setLayer _ Blank = Blank
+setLayer i (Polygon _ ps) = Polygon i ps
+setLayer i (PolygonCol _ ps) = PolygonCol i ps
+setLayer i (Circle _ x) = Circle i x
+setLayer i (ThickArc _ a b r w) = ThickArc i a b r w
+setLayer i (Line _ x) = Line i x
+setLayer i (Scale x y p) = Scale x y $ setLayer i p
+setLayer i (Translate x y p) = Translate x y $ setLayer i p
+setLayer i (Rotate x p) = Rotate x $ setLayer i p
+setLayer i (SetDepth x p) = SetDepth x $ setLayer i p
+setLayer i (Color x p) = Color x $ setLayer i p
+setLayer i (Pictures p) = Pictures $ map (setLayer i) p
+
+
 scale3 :: Float -> Float -> Point3 -> Point3
 {-# INLINE scale3 #-}
 scale3 a b (x,y,z) = (x*a,y*b,z)
@@ -134,19 +150,19 @@ makeArc rad (a,b) = zipWith rotateV as $ repeat (0,rad)
 circleSolid :: Float -> Picture
 {-# INLINE circleSolid #-}
 --circleSolid rad = polygon $ makeArc rad (0,2*pi)
-circleSolid = Circle
+circleSolid = Circle 0
 
 circle :: Float -> Picture
 {-# INLINE circle #-}
-circle rad = line $ makeArc rad (0,2*pi)
+circle rad = thickArc 0 (2*pi) rad 1
 
 text :: String -> Picture
 {-# INLINE text #-}
-text = Text
+text = Text 2
 
 line :: [Point2] -> Picture
 {-# INLINE line #-}
-line = Line
+line = Line 0
 
 thickLine :: [Point2] -> Float -> Picture
 {-# INLINE thickLine #-}
@@ -173,7 +189,7 @@ arc startA endA rad = thickArc startA endA rad 1
 
 thickArc :: Float -> Float -> Float -> Float -> Picture
 {-# INLINE thickArc #-}
-thickArc = ThickArc
+thickArc = ThickArc 0
 --thickArc startA endA rad wdth
 --    = thickLine (makeArc rad (startA,endA)) wdth