Index: client/dom/templates/html/frog/impl_Window.darttemplate |
diff --git a/client/dom/templates/html/frog/impl_Window.darttemplate b/client/dom/templates/html/frog/impl_Window.darttemplate |
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+// Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file |
+// for details. All rights reserved. Use of this source code is governed by a |
+// BSD-style license that can be found in the LICENSE file. |
+ |
+typedef Object ComputeValue(); |
+ |
+class _MeasurementRequest<T> { |
+ final ComputeValue computeValue; |
+ final Completer<T> completer; |
+ Object value; |
+ bool exception = false; |
+ _MeasurementRequest(this.computeValue, this.completer); |
+} |
+ |
+final _MEASUREMENT_MESSAGE = "DART-MEASURE"; |
+List<_MeasurementRequest> _pendingRequests; |
+List<TimeoutHandler> _pendingMeasurementFrameCallbacks; |
+bool _nextMeasurementFrameScheduled = false; |
+bool _firstMeasurementRequest = true; |
+ |
+void _maybeScheduleMeasurementFrame() { |
+ if (_nextMeasurementFrameScheduled) return; |
+ |
+ _nextMeasurementFrameScheduled = true; |
+ // postMessage gives us a way to receive a callback after the current |
+ // event listener has unwound but before the browser has repainted. |
+ if (_firstMeasurementRequest) { |
+ // Messages from other windows do not cause a security risk as |
+ // all we care about is that _onCompleteMeasurementRequests is called |
+ // after the current event loop is unwound and calling the function is |
+ // a noop when zero requests are pending. |
+ window.on.message.add((e) => _completeMeasurementFutures()); |
+ _firstMeasurementRequest = false; |
+ } |
+ |
+ // TODO(jacobr): other mechanisms such as setImmediate and |
+ // requestAnimationFrame may work better of platforms that support them. |
+ // The key is we need a way to execute code immediately after the current |
+ // event listener queue unwinds. |
+ window.postMessage(_MEASUREMENT_MESSAGE, "*"); |
+} |
+ |
+/** |
+ * Registers a [callback] which is called after the next batch of measurements |
+ * completes. Even if no measurements completed, the callback is triggered |
+ * when they would have completed to avoid confusing bugs if it happened that |
+ * no measurements were actually requested. |
+ */ |
+void _addMeasurementFrameCallback(TimeoutHandler callback) { |
+ if (_pendingMeasurementFrameCallbacks === null) { |
+ _pendingMeasurementFrameCallbacks = <TimeoutHandler>[]; |
+ _maybeScheduleMeasurementFrame(); |
+ } |
+ _pendingMeasurementFrameCallbacks.add(callback); |
+} |
+ |
+/** |
+ * Returns a [Future] whose value will be the result of evaluating |
+ * [computeValue] during the next safe measurement interval. |
+ * The next safe measurement interval is after the current event loop has |
+ * unwound but before the browser has rendered the page. |
+ * It is important that the [computeValue] function only queries the html |
+ * layout and html in any way. |
+ */ |
+Future _createMeasurementFuture(ComputeValue computeValue, |
+ Completer completer) { |
+ if (_pendingRequests === null) { |
+ _pendingRequests = <_MeasurementRequest>[]; |
+ _maybeScheduleMeasurementFrame(); |
+ } |
+ _pendingRequests.add(new _MeasurementRequest(computeValue, completer)); |
+ return completer.future; |
+} |
+ |
+/** |
+ * Complete all pending measurement futures evaluating them in a single batch |
+ * so that the the browser is guaranteed to avoid multiple layouts. |
+ */ |
+void _completeMeasurementFutures() { |
+ if (_nextMeasurementFrameScheduled == false) { |
+ // Ignore spurious call to this function. |
+ return; |
+ } |
+ |
+ _nextMeasurementFrameScheduled = false; |
+ // We must compute all new values before fulfilling the futures as |
+ // the onComplete callbacks for the futures could modify the DOM making |
+ // subsequent measurement calculations expensive to compute. |
+ if (_pendingRequests !== null) { |
+ for (_MeasurementRequest request in _pendingRequests) { |
+ try { |
+ request.value = request.computeValue(); |
+ } catch(var e) { |
+ request.value = e; |
+ request.exception = true; |
+ } |
+ } |
+ } |
+ |
+ final completedRequests = _pendingRequests; |
+ final readyMeasurementFrameCallbacks = _pendingMeasurementFrameCallbacks; |
+ _pendingRequests = null; |
+ _pendingMeasurementFrameCallbacks = null; |
+ if (completedRequests !== null) { |
+ for (_MeasurementRequest request in completedRequests) { |
+ if (request.exception) { |
+ request.completer.completeException(request.value); |
+ } else { |
+ request.completer.complete(request.value); |
+ } |
+ } |
+ } |
+ |
+ if (readyMeasurementFrameCallbacks !== null) { |
+ for (TimeoutHandler handler in readyMeasurementFrameCallbacks) { |
+ // TODO(jacobr): wrap each call to a handler in a try-catch block. |
+ handler(); |
+ } |
+ } |
+} |
+ |
+class $CLASSNAME$EXTENDS$IMPLEMENTS native "@*DOMWindow" { |
+ |
+ _DocumentJs get document() native "return this.document.documentElement;"; |
+ |
+ void requestLayoutFrame(TimeoutHandler callback) { |
+ _addMeasurementFrameCallback(callback); |
+ } |
+ |
+$!MEMBERS |
+} |