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// Copyright 2015 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef UI_ACCELERATED_WIDGET_MAC_WINDOW_RESIZE_HELPER_MAC_H_
#define UI_ACCELERATED_WIDGET_MAC_WINDOW_RESIZE_HELPER_MAC_H_
#include "base/lazy_instance.h"
#include "base/memory/scoped_refptr.h"
#include "base/task/single_thread_task_runner.h"
#include "ui/accelerated_widget_mac/accelerated_widget_mac_export.h"
namespace base {
class TimeDelta;
class WaitableEvent;
} // namespace base
namespace ui {
// WindowResizeHelperMac is used to make resize appear smooth. That is to
// say, make sure that the window size and the size of the contents being drawn
// in that window are resized in lock-step. This is accomplished by waiting
// inside AppKit drawing routines on the UI thread for the compositor to produce
// a frame of same size as the NSView that hosts an AcceleratedWidgetMac. When a
// resize occurs, the view controller can wait for a frame of the correct size
// by calling WindowResizeHelperMac::WaitForSingleTaskToRun() until a timeout
// occurs, or the corresponding AcceleratedWidgetMac has a renderer frame of the
// same size as its NSView.
//
// By posting tasks to the custom task_runner(), other threads indicate tasks
// that are required to pick up a new frame. In the ordinary run of things these
// would be posted to the |target_task_runner|; the UI thread given as an
// argument to Init(). Posting instead to task_runner() will cause the tasks to
// be posted to the UI thread (as usual), and will also enqueue them into a
// queue which will be read and run in WaitForSingleTaskToRun(), potentially
// before the task posted to the UI thread is run. Some care is taken (see
// WrappedTask) to make sure that the messages are only executed once.
//
// This is further complicated because, in order for a frame to appear, it is
// also necessary to run tasks posted by the ui::Compositor. To accomplish this,
// the task_runner() that WindowResizeHelperMac provides can be used to
// construct a ui::Compositor. When the Compositor posts tasks to it, they are
// enqueued in the aforementioned queue, which may be pumped by
// WindowResizeHelperMac::WaitForSingleTaskToRun().
class ACCELERATED_WIDGET_MAC_EXPORT WindowResizeHelperMac {
public:
static WindowResizeHelperMac* Get();
WindowResizeHelperMac(const WindowResizeHelperMac&) = delete;
WindowResizeHelperMac& operator=(const WindowResizeHelperMac&) = delete;
// Initializes the pumpable task_runner(), providing it with the task runner
// for UI thread tasks. task_runner() will be null before Init() is called,
// and WaitForSingleTaskToRun() will immediately return false.
void Init(
const scoped_refptr<base::SingleThreadTaskRunner>& target_task_runner);
// Because this class is global, many tests may want to do this setup
// repeatedly, so need some way to uninitialize as well.
void ShutdownForTests();
scoped_refptr<base::SingleThreadTaskRunner> task_runner() const;
// UI THREAD ONLY -----------------------------------------------------------
// Waits at most |max_delay| for a task to run. Returns true if a task ran,
// false if no task ran.
bool WaitForSingleTaskToRun(const base::TimeDelta& max_delay);
private:
friend struct base::LazyInstanceTraitsBase<WindowResizeHelperMac>;
WindowResizeHelperMac();
~WindowResizeHelperMac();
// This helper is needed to create a ScopedAllowWait inside the scope of a
// class where it is allowed.
static void EventTimedWait(base::WaitableEvent* event, base::TimeDelta delay);
// The task runner to which the helper will post tasks. This also maintains
// the task queue and does the actual work for WaitForSingleTaskToRun.
scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
};
} // namespace ui
#endif // UI_ACCELERATED_WIDGET_MAC_WINDOW_RESIZE_HELPER_MAC_H_
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