Document Reanimate.Effect, add overInterval.

Former-commit-id: 2dd9a3589a045126ab857807cca601495bd6bb7a

src/Reanimate.hs

@@ -86,6 +86,7 @@ module Reanimate
     Effect,
     overBeginning,
     overEnding,
+    overInterval,
     reverseE,
     delayE,
     applyE,
@@ -97,6 +98,7 @@ module Reanimate
     drawInE,
     drawOutE,
     fillInE,
+    scaleE,
     translateE,
     aroundCenterE,
     transitions,

src/Reanimate/Effect.hs

@@ -1,65 +1,130 @@
-module Reanimate.Effect where
+{-| Effects represent modifications applied to frames of the 'Animation'.
+Effects can (and usually do) depend on time.
+One or more effects can be applied over the entire duration of animation, or modified to affect
+only a specific portion at the beginning \/ middle \/ end of the animation.
+-}
+module Reanimate.Effect
+  ( -- * Primitive Effects
+  Effect
+  , fadeInE
+  , fadeOutE
+  , fadeLineInE
+  , fadeLineOutE
+  , fillInE
+  , drawInE
+  , drawOutE
+  , translateE
+  , scaleE
+  , constE
+  -- * Modifying Effects
+  , overBeginning
+  , overEnding
+  , overInterval
+  , reverseE
+  , delayE
+  , aroundCenterE
+  -- * Applying Effects to Animations
+  , applyE
+  ) where
 
 import           Graphics.SvgTree    (Tree)
 import           Reanimate.Animation
 import           Reanimate.Svg
 
-type Effect = Double -> Double -> Tree -> Tree
+-- | An Effect represents a modification of a SVG 'Tree' that can vary with time.
+type Effect = Duration -- ^ Duration of the effect (in seconds)
+           -> Time -- ^ Time elapsed from when the effect started (in seconds)
+           -> Tree -- ^ Image to be modified
+           -> Tree -- ^ Image after modification
 
-overBeginning :: Double -> Effect -> Effect
+-- | Modify the effect so that it only applies to the initial part of the animation.
-overBeginning maxT fn = \_d t ->
+overBeginning :: Duration -- ^ Duration of the initial segment of the animation over which the Effect should be applied
+              -> Effect -- ^ The Effect to modify
+              -> Effect -- ^ Effect which will only affect the initial segment of the animation
+overBeginning maxT effect _d t =
   if t < maxT
-    then fn maxT t
+    then effect maxT t
     else id
 
-overEnding :: Double -> Effect -> Effect
+-- | Modify the effect so that it only applies to the ending part of the animation.
-overEnding minT fn d t =
+overEnding :: Duration -- ^ Duration of the ending segment of the animation over which the Effect should be applied
+           -> Effect  -- ^ The Effect to modify
+           -> Effect -- ^ Effect which will only affect the ending segment of the animation
+overEnding minT effect d t =
   if t >= blankDur
-    then fn minT (t-blankDur)
+    then effect minT (t-blankDur)
     else id
   where
     blankDur = d-minT
 
+-- | Modify the effect so that it only applies within given interval of animation's running time.
+overInterval :: Time -- ^ time after start of animation when the effect should start
+             -> Time -- ^ time after start of the animation when the effect should finish
+             -> Effect  -- ^ The Effect to modify
+             -> Effect -- ^ Effect which will only affect the specified interval within the animation
+overInterval start end effect _d t = 
+  if start <= t && t <= end
+    then effect dur ((t - start) / dur)
+    else id
+  where
+    dur = end - start
+
+-- | @reverseE effect@ starts where the @effect@ ends and vice versa.
 reverseE :: Effect -> Effect
 reverseE fn = \d t -> fn d (d-t)
 
-delayE :: Double -> Effect -> Effect
+-- | Delay the effect so that it only starts after specified duration and then runs till the end of animation.
+delayE :: Duration -> Effect -> Effect
 delayE delayT fn = \d t -> overEnding (d-delayT) fn d t
 
+-- | Modify the animation by applying the effect. If desired, you can apply multiple effects to single animation by calling this function multiple times.
 applyE :: Effect -> Animation -> Animation
 applyE fn (Animation d genFrame) = Animation d $ \t -> fn d (d*t) $ genFrame t
 
+-- | Build an effect from an image-modifying function. This effect does not change as time passes.
 constE :: (Tree -> Tree) -> Effect
 constE fn _d _t = fn
 
+-- | Change image opacity from 0 to 1.
 fadeInE :: Effect
 fadeInE d t = withGroupOpacity (t/d)
 
+-- | Change image opacity from 1 to 0. Reverse of 'fadeInE'.
 fadeOutE :: Effect
 fadeOutE = reverseE fadeInE
 
+-- | Change stroke width from 0 to given value.
 fadeLineInE :: Double -> Effect
 fadeLineInE w d t = withStrokeWidth (w*(t/d))
 
+-- | Change stroke width from given value to 0. Reverse of 'fadeLineInE'.
 fadeLineOutE :: Double -> Effect
 fadeLineOutE = reverseE . fadeLineInE
 
+-- | Effect of progressively drawing the image. Note that this will only affect primitive shapes (see 'pathify').
 drawInE :: Effect
 drawInE d t = withFillOpacity 0 . partialSvg (t/d) . pathify
 
+-- | Reverse of 'drawInE'.
 drawOutE :: Effect
 drawOutE = reverseE drawInE
 
+-- | Change fill opacity from 0 to 1.
 fillInE :: Effect
 fillInE d t = withFillOpacity f
   where
     f = t/d
 
+-- | Change scale from 1 to given value.
 scaleE :: Double -> Effect
 scaleE target d t = scale (1 + (target-1) * t/d)
 
+-- | Move the image from its current position to the target x y coordinates.
 translateE :: Double -> Double -> Effect
 translateE x y d t = translate (x * t/d) (y * t/d)
 
+-- | Transform the effect so that the image passed to the effect's image-modifying 
+-- function has coordinates (0, 0) shifted to the center of its bounding box.
+-- Also see 'aroundCenter'.
 aroundCenterE :: Effect -> Effect
 aroundCenterE e d t = aroundCenter (e d t)

src/Reanimate/Svg/Constructors.hs

@@ -89,7 +89,7 @@ rotateAroundCenter a t =
     (x,y,w,h) = boundingBox t
 
 -- | @arounCenter f image@ first moves the image so the center of its bounding box is at the origin @(0, 0)@,
--- applies transformation @f@ to it and then moves the transformed image to it's original position.
+-- applies transformation @f@ to it and then moves the transformed image back to its original position.
 aroundCenter :: (Tree -> Tree) -> Tree -> Tree
 aroundCenter fn t =
     translate (-offsetX) (-offsetY) $ fn $ translate offsetX offsetY t
@@ -104,7 +104,7 @@ aroundCenter fn t =
 scale :: Double -> Tree -> Tree
 scale a = withTransformations [Scale a Nothing]
 
--- | @scaleToSize width height@ resizes the image so that it's bounding box has corresponding @width@ and @height@.
+-- | @scaleToSize width height@ resizes the image so that its bounding box has corresponding @width@ and @height@.
 scaleToSize :: Double -> Double -> Tree -> Tree
 scaleToSize w h t =
     scaleXY (w/w') (h/h') t