Implement measurement using futures

client/layout/ViewLayout.dart

Index: client/layout/ViewLayout.dart
diff --git a/client/layout/ViewLayout.dart b/client/layout/ViewLayout.dart
index b86155c720463a840f98df3503ba2bde729572fe..e06dae2c25afdc8c91cf19295741a1d42a6ae054 100644
--- a/client/layout/ViewLayout.dart
+++ b/client/layout/ViewLayout.dart
@@ -27,12 +27,12 @@ interface Positionable {
 class LayoutParams {
   // TODO(jmesserly): should be const, but there's a bug in DartC preventing us
   // from calling "window." in an initializer. See b/5332777
-  CSSStyleDeclaration style;
+  Future<CSSStyleDeclaration> style;
 
   int get layer() => 0;
 
   LayoutParams(Element node) {
-    style = window.getComputedStyle(node, '');
+    style = node.computedStyle;
   }
 }
 
@@ -71,6 +71,7 @@ class ViewLayout {
    * to determine how this view should be laid out.
    */
   LayoutParams layoutParams;
+  Future<ElementRect> _cachedViewRect;
 
   /** The view that this layout belongs to. */
   final Positionable view;
@@ -82,7 +83,7 @@ class ViewLayout {
    */
   int _measuredLeft, _measuredTop, _measuredWidth, _measuredHeight;
 
-  ViewLayout(this.view) {}
+  ViewLayout(this.view);
 
   /**
    * Creates the appropriate view layout, depending on the properties.
@@ -101,10 +102,19 @@ class ViewLayout {
     return view.customStyle['display'] == "-dart-grid";
   }
 
-  CSSStyleDeclaration get _style() => layoutParams.style;
+  CSSStyleDeclaration get _style() => layoutParams.style.value;
 
-  int get currentWidth() => view.node.offsetWidth;
-  int get currentHeight() => view.node.offsetHeight;
+  void cacheExistingBrowserLayout() {
+    _cachedViewRect = view.node.rect;
+  }
+
+  int get currentWidth() {
+    return _cachedViewRect.value.offset.width;

[nweiz, 2011/10/28 03:58:38]

What happens when _cachedViewRect hasn't fired yet? Seems like an NPE isn't
ideal... and if _cachedViewRect is always going to be concrete, why not store
ElementRect rather than a future?

Also, what if cacheExistingBrowserLayout hasn't been called yet?

[Jacob, 2011/10/31 22:09:50]

by design it will always have fired due to appropriate calls to
requestLayoutFrame in the code that uses this.
This way we should get the right "future not available exception" instead of
just a NPE resulting in clearer error messages as well as making the code
simpler and more efficient as we avoid attaching completion listeners to each of
the individual futures.

[nweiz, 2011/11/01 00:49:22]

Oh, futures throw an error when value doesn't exist? That makes sense.

+  }
+
+  int get currentHeight() {
+    return _cachedViewRect.value.offset.height;
+  }
 
   int get borderLeftWidth() => _toPixels(_style.borderLeftWidth);

[nweiz, 2011/10/28 03:58:38]

Can't _style be null sometimes?

[Jacob, 2011/10/31 22:09:50]

it can't be null, however a future not available yet exception could fire if the
user doesn't use this correctly.
This is ugly but I can't think of a cleaner way to modify this api to work
acceptably with async layout. If you or John can think of a better way to modify
this, let me know.

[nweiz, 2011/11/01 00:49:22]

The fact that it fires a "future not completed" error rather than an NPE makes
this better. I think the ideal scenario is to have all these properties return
Futures, but that's not really practical without more fluid language support for
async.

   int get borderTopWidth() => _toPixels(_style.borderTopWidth);
@@ -112,9 +122,10 @@ class ViewLayout {
   int get borderBottomWidth() => _toPixels(_style.borderBottomWidth);
   int get borderWidth() => borderLeftWidth + borderRightWidth;
   int get borderHeight() => borderTopWidth + borderBottomWidth;
-
+ 

[nweiz, 2011/10/28 03:58:38]

Style nit: trailing whitespace

[Jacob, 2011/10/31 22:09:50]

Done.

   /** Implements the custom layout computation. */
-  bool measureLayout(int width, int height) => false;
+  void measureLayout(Future<Size> size, Completer<bool> changed) {
+  }
 
   /**
    * Positions the view within its parent container.
@@ -129,8 +140,9 @@ class ViewLayout {
     // Note: we need to save the client height
     _measuredWidth = width - borderWidth;
     _measuredHeight = height - borderHeight;
-
-    measureLayout(_measuredWidth, _measuredHeight);
+    final completer = new Completer<Size>();
+    completer.complete(new Size(_measuredWidth, _measuredHeight));
+    measureLayout(completer.future, null);
   }
 
   /** Applies the layout to the node. */
@@ -176,7 +188,7 @@ class ViewLayout {
   }
 
   int measureWidth(ViewLayout parent, ContentSizeMode mode) {
-    final style = layoutParams.style;
+    final style = layoutParams.style.value;
     switch (mode) {
       case ContentSizeMode.MIN:
         return _styleToPixels(
@@ -189,7 +201,7 @@ class ViewLayout {
   }
 
   int measureHeight(ViewLayout parent, ContentSizeMode mode) {
-    final style = layoutParams.style;
+    final style = layoutParams.style.value;
     switch (mode) {
       case ContentSizeMode.MIN:
         return _styleToPixels(