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<dl class="meta">
<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/171068">171068</a></dd>
<dt>Author</dt> <dd>timothy_horton@apple.com</dd>
<dt>Date</dt> <dd>2014-07-14 11:11:46 -0700 (Mon, 14 Jul 2014)</dd>
</dl>

<h3>Log Message</h3>
<pre>[iOS] Throttle painting using a UI-process-side CADisplayLink
https://bugs.webkit.org/show_bug.cgi?id=134879
&lt;rdar://problem/17641699&gt;

Reviewed by Simon Fraser.

Just waiting for CA to commit is insufficient to actually throttle to 60fps,
because nothing will block the main runloop from spinning.

Instead, listen to a CADisplayLink, and send didUpdate to the WebProcess
the first time it fires after we commit. This is not a guarantee that
our content is on the screen, but we don't have any way to make that guarantee yet.

This will throttle painting, rAF, etc. to the display refresh rate.

* UIProcess/mac/RemoteLayerTreeDrawingAreaProxy.h:
* UIProcess/mac/RemoteLayerTreeDrawingAreaProxy.mm:
(-[OneShotDisplayLinkHandler initWithDrawingAreaProxy:]):
(-[OneShotDisplayLinkHandler dealloc]):
(-[OneShotDisplayLinkHandler displayLinkFired:]):
(-[OneShotDisplayLinkHandler invalidate]):
(-[OneShotDisplayLinkHandler schedule]):
(WebKit::RemoteLayerTreeDrawingAreaProxy::RemoteLayerTreeDrawingAreaProxy):
(WebKit::RemoteLayerTreeDrawingAreaProxy::~RemoteLayerTreeDrawingAreaProxy):
(WebKit::RemoteLayerTreeDrawingAreaProxy::commitLayerTree):
(WebKit::RemoteLayerTreeDrawingAreaProxy::didRefreshDisplay):
(WebKit::RemoteLayerTreeDrawingAreaProxy::coreAnimationDidCommitLayers): Deleted.</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWebKit2ChangeLog">trunk/Source/WebKit2/ChangeLog</a></li>
<li><a href="#trunkSourceWebKit2UIProcessmacRemoteLayerTreeDrawingAreaProxyh">trunk/Source/WebKit2/UIProcess/mac/RemoteLayerTreeDrawingAreaProxy.h</a></li>
<li><a href="#trunkSourceWebKit2UIProcessmacRemoteLayerTreeDrawingAreaProxymm">trunk/Source/WebKit2/UIProcess/mac/RemoteLayerTreeDrawingAreaProxy.mm</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceWebKit2ChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebKit2/ChangeLog (171067 => 171068)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebKit2/ChangeLog        2014-07-14 17:16:57 UTC (rev 171067)
+++ trunk/Source/WebKit2/ChangeLog        2014-07-14 18:11:46 UTC (rev 171068)
</span><span class="lines">@@ -1,3 +1,33 @@
</span><ins>+2014-07-14  Tim Horton  &lt;timothy_horton@apple.com&gt;
+
+        [iOS] Throttle painting using a UI-process-side CADisplayLink
+        https://bugs.webkit.org/show_bug.cgi?id=134879
+        &lt;rdar://problem/17641699&gt;
+
+        Reviewed by Simon Fraser.
+
+        Just waiting for CA to commit is insufficient to actually throttle to 60fps,
+        because nothing will block the main runloop from spinning.
+
+        Instead, listen to a CADisplayLink, and send didUpdate to the WebProcess
+        the first time it fires after we commit. This is not a guarantee that
+        our content is on the screen, but we don't have any way to make that guarantee yet.
+
+        This will throttle painting, rAF, etc. to the display refresh rate.
+
+        * UIProcess/mac/RemoteLayerTreeDrawingAreaProxy.h:
+        * UIProcess/mac/RemoteLayerTreeDrawingAreaProxy.mm:
+        (-[OneShotDisplayLinkHandler initWithDrawingAreaProxy:]):
+        (-[OneShotDisplayLinkHandler dealloc]):
+        (-[OneShotDisplayLinkHandler displayLinkFired:]):
+        (-[OneShotDisplayLinkHandler invalidate]):
+        (-[OneShotDisplayLinkHandler schedule]):
+        (WebKit::RemoteLayerTreeDrawingAreaProxy::RemoteLayerTreeDrawingAreaProxy):
+        (WebKit::RemoteLayerTreeDrawingAreaProxy::~RemoteLayerTreeDrawingAreaProxy):
+        (WebKit::RemoteLayerTreeDrawingAreaProxy::commitLayerTree):
+        (WebKit::RemoteLayerTreeDrawingAreaProxy::didRefreshDisplay):
+        (WebKit::RemoteLayerTreeDrawingAreaProxy::coreAnimationDidCommitLayers): Deleted.
+
</ins><span class="cx"> 2014-07-14  Dan Bernstein  &lt;mitz@apple.com&gt;
</span><span class="cx"> 
</span><span class="cx">         &lt;rdar://problem/17657391&gt; [iOS] Networking process writes persistent credentials to the keychain
</span></span></pre></div>
<a id="trunkSourceWebKit2UIProcessmacRemoteLayerTreeDrawingAreaProxyh"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebKit2/UIProcess/mac/RemoteLayerTreeDrawingAreaProxy.h (171067 => 171068)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebKit2/UIProcess/mac/RemoteLayerTreeDrawingAreaProxy.h        2014-07-14 17:16:57 UTC (rev 171067)
+++ trunk/Source/WebKit2/UIProcess/mac/RemoteLayerTreeDrawingAreaProxy.h        2014-07-14 18:11:46 UTC (rev 171068)
</span><span class="lines">@@ -31,8 +31,9 @@
</span><span class="cx"> #include &lt;WebCore/FloatPoint.h&gt;
</span><span class="cx"> #include &lt;WebCore/IntPoint.h&gt;
</span><span class="cx"> #include &lt;WebCore/IntSize.h&gt;
</span><del>-#include &lt;WebCore/RunLoopObserver.h&gt;
</del><span class="cx"> 
</span><ins>+OBJC_CLASS OneShotDisplayLinkHandler;
+
</ins><span class="cx"> namespace WebKit {
</span><span class="cx"> 
</span><span class="cx"> class RemoteLayerTreeTransaction;
</span><span class="lines">@@ -47,11 +48,11 @@
</span><span class="cx"> 
</span><span class="cx">     void acceleratedAnimationDidStart(uint64_t layerID, const String&amp; key, double startTime);
</span><span class="cx"> 
</span><del>-    void coreAnimationDidCommitLayers();
-
</del><span class="cx">     uint64_t nextLayerTreeTransactionID() const { return m_pendingLayerTreeTransactionID + 1; }
</span><span class="cx">     uint64_t lastCommittedLayerTreeTransactionID() const { return m_transactionIDForPendingCACommit; }
</span><span class="cx"> 
</span><ins>+    void didRefreshDisplay(double timestamp);
+
</ins><span class="cx"> private:
</span><span class="cx">     virtual void sizeDidChange() override;
</span><span class="cx">     virtual void deviceScaleFactorDidChange() override;
</span><span class="lines">@@ -96,13 +97,13 @@
</span><span class="cx">     RetainPtr&lt;CALayer&gt; m_tileMapHostLayer;
</span><span class="cx">     RetainPtr&lt;CALayer&gt; m_exposedRectIndicatorLayer;
</span><span class="cx"> 
</span><del>-    std::unique_ptr&lt;WebCore::RunLoopObserver&gt; m_layerCommitObserver;
-
</del><span class="cx">     uint64_t m_pendingLayerTreeTransactionID;
</span><span class="cx">     uint64_t m_lastVisibleTransactionID;
</span><span class="cx">     uint64_t m_transactionIDForPendingCACommit;
</span><span class="cx"> 
</span><span class="cx">     CallbackMap m_callbacks;
</span><ins>+
+    RetainPtr&lt;OneShotDisplayLinkHandler&gt; m_displayLinkHandler;
</ins><span class="cx"> };
</span><span class="cx"> 
</span><span class="cx"> DRAWING_AREA_PROXY_TYPE_CASTS(RemoteLayerTreeDrawingAreaProxy, type() == DrawingAreaTypeRemoteLayerTree);
</span></span></pre></div>
<a id="trunkSourceWebKit2UIProcessmacRemoteLayerTreeDrawingAreaProxymm"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebKit2/UIProcess/mac/RemoteLayerTreeDrawingAreaProxy.mm (171067 => 171068)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebKit2/UIProcess/mac/RemoteLayerTreeDrawingAreaProxy.mm        2014-07-14 17:16:57 UTC (rev 171067)
+++ trunk/Source/WebKit2/UIProcess/mac/RemoteLayerTreeDrawingAreaProxy.mm        2014-07-14 18:11:46 UTC (rev 171068)
</span><span class="lines">@@ -40,8 +40,62 @@
</span><span class="cx"> using namespace IPC;
</span><span class="cx"> using namespace WebCore;
</span><span class="cx"> 
</span><del>-static const CFIndex didCommitLayersRunLoopOrder = (CFIndex)RunLoopObserver::WellKnownRunLoopOrders::CoreAnimationCommit + 1;
</del><ins>+// FIXME: Mac will need something similar; we should figure out how to share this with DisplayRefreshMonitor without
+// breaking WebKit1 behavior or WebKit2-WebKit1 coexistence.
+#if PLATFORM(IOS)
+@interface OneShotDisplayLinkHandler : NSObject {
+    WebKit::RemoteLayerTreeDrawingAreaProxy* _drawingAreaProxy;
+    CADisplayLink *_displayLink;
+}
</ins><span class="cx"> 
</span><ins>+- (id)initWithDrawingAreaProxy:(WebKit::RemoteLayerTreeDrawingAreaProxy*)drawingAreaProxy;
+- (void)displayLinkFired:(CADisplayLink *)sender;
+- (void)invalidate;
+- (void)schedule;
+
+@end
+
+@implementation OneShotDisplayLinkHandler
+
+- (id)initWithDrawingAreaProxy:(WebKit::RemoteLayerTreeDrawingAreaProxy*)drawingAreaProxy
+{
+    if (self = [super init]) {
+        _drawingAreaProxy = drawingAreaProxy;
+        // Note that CADisplayLink retains its target (self), so a call to -invalidate is needed on teardown.
+        _displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(displayLinkFired:)];
+        [_displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
+        _displayLink.paused = YES;
+    }
+    return self;
+}
+
+- (void)dealloc
+{
+    ASSERT(!_displayLink);
+    [super dealloc];
+}
+
+- (void)displayLinkFired:(CADisplayLink *)sender
+{
+    ASSERT(isMainThread());
+    _drawingAreaProxy-&gt;didRefreshDisplay(sender.timestamp);
+    _displayLink.paused = YES;
+}
+
+- (void)invalidate
+{
+    [_displayLink invalidate];
+    _displayLink = nullptr;
+}
+
+- (void)schedule
+{
+    _displayLink.paused = NO;
+}
+
+@end
+#endif
+
</ins><span class="cx"> namespace WebKit {
</span><span class="cx"> 
</span><span class="cx"> RemoteLayerTreeDrawingAreaProxy::RemoteLayerTreeDrawingAreaProxy(WebPageProxy* webPageProxy)
</span><span class="lines">@@ -51,6 +105,9 @@
</span><span class="cx">     , m_pendingLayerTreeTransactionID(0)
</span><span class="cx">     , m_lastVisibleTransactionID(0)
</span><span class="cx">     , m_transactionIDForPendingCACommit(0)
</span><ins>+#if PLATFORM(IOS)
+    , m_displayLinkHandler(adoptNS([[OneShotDisplayLinkHandler alloc] initWithDrawingAreaProxy:this]))
+#endif
</ins><span class="cx"> {
</span><span class="cx"> #if USE(IOSURFACE)
</span><span class="cx">     // We don't want to pool surfaces in the UI process.
</span><span class="lines">@@ -62,16 +119,16 @@
</span><span class="cx"> 
</span><span class="cx">     if (m_webPageProxy-&gt;preferences().tiledScrollingIndicatorVisible())
</span><span class="cx">         initializeDebugIndicator();
</span><del>-
-    m_layerCommitObserver = RunLoopObserver::create(didCommitLayersRunLoopOrder, [this]() {
-        this-&gt;coreAnimationDidCommitLayers();
-    });
</del><span class="cx"> }
</span><span class="cx"> 
</span><span class="cx"> RemoteLayerTreeDrawingAreaProxy::~RemoteLayerTreeDrawingAreaProxy()
</span><span class="cx"> {
</span><span class="cx">     m_callbacks.invalidate(CallbackBase::Error::OwnerWasInvalidated);
</span><span class="cx">     m_webPageProxy-&gt;process().removeMessageReceiver(Messages::RemoteLayerTreeDrawingAreaProxy::messageReceiverName(), m_webPageProxy-&gt;pageID());
</span><ins>+
+#if PLATFORM(IOS)
+    [m_displayLinkHandler invalidate];
+#endif
</ins><span class="cx"> }
</span><span class="cx"> 
</span><span class="cx"> void RemoteLayerTreeDrawingAreaProxy::sizeDidChange()
</span><span class="lines">@@ -167,7 +224,11 @@
</span><span class="cx">         asLayer(m_debugIndicatorLayerTreeHost-&gt;rootLayer()).name = @&quot;Indicator host root&quot;;
</span><span class="cx">     }
</span><span class="cx"> 
</span><del>-    m_layerCommitObserver-&gt;schedule();
</del><ins>+#if PLATFORM(IOS)
+    [m_displayLinkHandler schedule];
+#else
+    didRefreshDisplay(monotonicallyIncreasingTime());
+#endif
</ins><span class="cx"> }
</span><span class="cx"> 
</span><span class="cx"> void RemoteLayerTreeDrawingAreaProxy::acceleratedAnimationDidStart(uint64_t layerID, const String&amp; key, double startTime)
</span><span class="lines">@@ -302,10 +363,8 @@
</span><span class="cx">     }
</span><span class="cx"> }
</span><span class="cx"> 
</span><del>-void RemoteLayerTreeDrawingAreaProxy::coreAnimationDidCommitLayers()
</del><ins>+void RemoteLayerTreeDrawingAreaProxy::didRefreshDisplay(double)
</ins><span class="cx"> {
</span><del>-    m_layerCommitObserver-&gt;invalidate();
-
</del><span class="cx">     if (!m_webPageProxy-&gt;isValid())
</span><span class="cx">         return;
</span><span class="cx"> 
</span></span></pre>
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