From ea559050160e045c61cc6a0ebee66990515ac2e3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=B8ren=20Debois?= <debois@itu.dk>
Date: Wed, 30 Mar 2016 21:19:06 +0200
Subject: [PATCH] Filter scroll events.

---
 examples/Demo.elm       |  5 +----
 examples/Demo/Grid.elm  | 35 ++++++++++++++++++++++++++++++
 src/Material/Layout.elm | 47 ++++++++++++++++++++++++++++-------------
 3 files changed, 68 insertions(+), 19 deletions(-)

diff --git a/examples/Demo.elm b/examples/Demo.elm
index fd33b64..b6e8d1d 100644
--- a/examples/Demo.elm
+++ b/examples/Demo.elm
@@ -13,7 +13,6 @@ import Material.Layout as Layout exposing (defaultLayoutModel)
 
 import Material exposing (lift, lift')
 import Material.Style as Style
-import Material.Icon as Icon
 import Material
 
 import Demo.Buttons
@@ -25,8 +24,6 @@ import Demo.Badges
 
 -- MODEL
 
-x = 0 + "foo"
-
 
 layoutModel : Layout.Model
 layoutModel =
@@ -196,7 +193,7 @@ init = (model, Effects.none)
 
 inputs : List (Signal.Signal Action)
 inputs =
-  [ Layout.setupSizeChangeSignal LayoutAction
+  [ Layout.setupSignals LayoutAction
   ]
 
 
diff --git a/examples/Demo/Grid.elm b/examples/Demo/Grid.elm
index 3a92e8e..320f14c 100644
--- a/examples/Demo/Grid.elm
+++ b/examples/Demo/Grid.elm
@@ -3,6 +3,8 @@ module Demo.Grid where
 import Material.Grid exposing (..)
 import Material.Style exposing (Style, css)
 
+import Markdown
+
 import Html exposing (..)
 
 -- Cell styling
@@ -50,3 +52,36 @@ view =
   ]
 
 
+intro : Html
+intro = """
+From the
+[Material Design Lite documentation](http://www.getmdl.io/components/#layout-section/grid):
+
+> The Material Design Lite (MDL) grid component is a simplified method for laying
+> out content for multiple screen sizes. It reduces the usual coding burden
+> required to correctly display blocks of content in a variety of display
+> conditions.
+>
+> The MDL grid is defined and enclosed by a container element. A grid has 12
+> columns in the desktop screen size, 8 in the tablet size, and 4 in the phone
+> size, each size having predefined margins and gutters. Cells are laid out
+> sequentially in a row, in the order they are defined, with some exceptions:
+>
+>   - If a cell doesn't fit in the row in one of the screen sizes, it flows
+>     into the following line.
+>   - If a cell has a specified column size equal to or larger than the number
+>     of columns for the current screen size, it takes up the entirety of its
+>     row.
+
+#### See also
+
+ - [Demo source code](https://github.com/debois/elm-mdl/blob/master/examples/Demo/Grid.elm)
+ - [elm-mdl package documentation](http://package.elm-lang.org/packages/debois/elm-mdl/latest/Material-Grid)
+ - [Material Design Specification](https://www.google.com/design/spec/layout/responsive-ui.html#responsive-ui-grid)
+ - [Material Design Lite documentation](http://www.getmdl.io/components/#layout-section/grid)
+
+#### Demo
+
+""" |> Markdown.toHtml
+
+
diff --git a/src/Material/Layout.elm b/src/Material/Layout.elm
index 1eb31dd..bf046e9 100644
--- a/src/Material/Layout.elm
+++ b/src/Material/Layout.elm
@@ -1,5 +1,5 @@
 module Material.Layout
-  ( setupSizeChangeSignal
+  ( setupSignals
   , Mode(..), Model, defaultLayoutModel, initState
   , Action(SwitchTab, ToggleDrawer), update
   , row, spacer, title, navigation, link
@@ -39,7 +39,7 @@ module Material.Layout
 @docs row, spacer, title, navigation, link
 
 # Setup
-@docs setupSizeChangeSignal
+@docs setupSignals
 -}
 
 
@@ -63,21 +63,38 @@ import DOM
 -- SETUP
 
 
-{-| Setup signal for registering changes in display size. Use with StartApp
-like so, supposing you have a `LayoutAction` encapsulating actions of the
+scrollMailbox : Signal.Mailbox Float
+scrollMailbox = Signal.mailbox 0.0
+
+
+{-| Setup various signals layout needs (viewport size changes, scrolling). Use
+with StartApp like so, supposing you have a `LayoutAction` encapsulating
+actions of the
 layout:
 
     inputs : List (Signal.Signal Action)
     inputs =
-      [ Layout.setupSizeChangeSignal LayoutAction
+      [ Layout.setupSignals LayoutAction
       ]
 -}
-setupSizeChangeSignal : (Action -> a) -> Signal a
-setupSizeChangeSignal f =
-  Window.width
-  |> Signal.map ((>) 1024)
-  |> Signal.dropRepeats
-  |> Signal.map (SmallScreen >> f)
+setupSignals : (Action -> a) -> Signal a
+setupSignals f =
+  {- NB! mergeMany propagates only the first provided signal if more than one
+     signal changes value at the same time.  We are processing two signals: (1)
+     viewport size changes and (2) scrolling of main contents.  It /appears/
+     that these cannot happen at the same time, so the following should be
+     safe. 
+  -}
+  Signal.mergeMany
+    [ Window.width
+        |> Signal.map ((>) 1024)
+        |> Signal.dropRepeats
+        |> Signal.map (SmallScreen >> f)
+    , scrollMailbox.signal
+        |> Signal.map ((<) 0.0)
+        |> Signal.dropRepeats
+        |> Signal.map (ScrollContents >> f) 
+    ]
 
 
 -- MODEL
@@ -172,7 +189,7 @@ type Action
   -- Private
   | SmallScreen Bool -- True means small screen
   | ScrollTab Float
-  | ScrollContents Float
+  | ScrollContents Bool -- True means strictly positive scrollTop
   | Ripple Int Ripple.Action
   | Click 
   | TransitionEnd
@@ -214,12 +231,12 @@ update action model =
       (model, Effects.none) -- TODO
 
 
-    ScrollContents scrollTop -> 
+    ScrollContents isScrolled -> 
       let 
         headerVisible = state.isSmallScreen || model.fixedHeader
         state' = 
           { state 
-          | isCompact = scrollTop > 0 
+          | isCompact = isScrolled
           , isAnimating = headerVisible 
           }
       in
@@ -505,7 +522,7 @@ view addr model { drawer, header, tabs, main } =
             ( class "mdl-layout__content" 
             :: (
               if isWaterfall model.mode then 
-                [ on "scroll" (DOM.target DOM.scrollTop) (ScrollContents >> Signal.message addr) ]
+                [ on "scroll" (DOM.target DOM.scrollTop) (Signal.message scrollMailbox.address) ]
               else 
                 []
               )