Wrapperless dart:html generator

client/dom/templates/html/frog/impl_Window.darttemplate

+// 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
+}