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// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef CC_TREES_SWAP_PROMISE_H_
#define CC_TREES_SWAP_PROMISE_H_
#include <stdint.h>
#include "cc/cc_export.h"
#include "components/viz/common/quads/compositor_frame_metadata.h"
namespace cc {
// When a change to the compositor's state/invalidation/whatever happens, a
// Swap Promise can be inserted into LayerTreeHost/LayerTreeImpl, to track
// whether the compositor's reply to the new state/invaliadtion/whatever is
// completed in the compositor, i.e. the compositor knows it has been sent
// to its output or not.
//
// If the commit results in a successful activation of the pending layer tree,
// SwapPromise::DidActivate() will be called.
//
// If the new compositor state is goint to be sent to the output,
// SwapPromise::WillSwap() will be called before the swap and
// SwapPromise::DidSwap() will be called once the swap is over.
//
// If the scheduler fails to activate the pending tree, or the compositor
// fails to send its new state to the output, SwapPromise::DidNotSwap() will
// be called. Note that it is possible to activate, and subsequently not swap.
//
// Promises complete afer either DidSwap() or DidNotSwap() is called, thus
// there are three possible call sequences:
// DidNotSwap()
// DidActivate() ; WillSwap(); DidSwap()
// DidActivate() ; DidNotSwap()
//
// Clients that wish to use SwapPromise should have a subclass that defines
// the behavior of DidActivate(), WillSwap(), DidSwap() and DidNotSwap(). Notice
// that the promise can be broken at either main or impl thread, e.g. commit
// fails on main thread, new frame data has no actual damage so
// LayerTreeHostImpl::SwapBuffers() bails out early on impl thread, so don't
// assume that DidNotSwap() method is called at a particular thread. It is
// better to let the subclass carry thread-safe member data and operate on that
// member data in DidNotSwap().
class CC_EXPORT SwapPromise {
public:
enum DidNotSwapReason {
SWAP_FAILS,
COMMIT_FAILS,
COMMIT_NO_UPDATE,
ACTIVATION_FAILS,
};
SwapPromise() {}
virtual ~SwapPromise() {}
virtual void DidActivate() = 0;
virtual void WillSwap(viz::CompositorFrameMetadata* metadata) = 0;
virtual void DidSwap() = 0;
virtual void DidNotSwap(DidNotSwapReason reason) = 0;
// This is called when the main thread starts a (blocking) commit
virtual void OnCommit() {}
// A non-zero trace id identifies a trace flow object that is embedded in the
// swap promise. This can be used for registering additional flow steps to
// visualize the object's path through the system.
virtual int64_t TraceId() const = 0;
};
} // namespace cc
#endif // CC_TREES_SWAP_PROMISE_H_
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