mac: Implement custom AppKit Enter Fullscreen transition.

chrome/browser/ui/cocoa/browser_window_enter_fullscreen_transition.h

+// Copyright 2015 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 CHROME_BROWSER_UI_COCOA_BROWSER_WINDOW_FULLSCREEN_TRANSITION_H_
+#define CHROME_BROWSER_UI_COCOA_BROWSER_WINDOW_FULLSCREEN_TRANSITION_H_
+
+#import <Cocoa/Cocoa.h>
+
+// This class is responsible for managing the custom transition of a
+// BrowserWindow from its normal state into an AppKit Fullscreen state.
+//
+// By default, when AppKit Fullscreens a window, it creates a new virtual
+// desktop and slides it in from the right of the screen. At the same time, the
+// old virtual desktop slides off to the left. This animation takes one second,
+// and the time is not customizable without elevated privileges or a
+// self-modifying binary
+// (https://code.google.com/p/chromium/issues/detail?id=414527). During that
+// second, no user interaction is possible.
+//
+// The default implementation of the AppKit transition smoothly animates a
+// window from its original size to the full size of the screen. At the
+// beginning of the animation, it takes a snapshot of the window's current
+// state. Then it resizes the window, calls drawRect: (theorized, not tested),
+// and takes a snapshot of the window's final state. The animation is a simple
+// crossfade between the two snapshots. This has a flaw. Frequently, the
+// renderer has not yet drawn content for the resized window by the time
+// drawRect: is called. As a result, the animation is effectively a no-op. When
+// the animation is finished, the new web content flashes in.
+//
+// The window's delegate can override two methods to customize the transition.
+//  -customWindowsToEnterFullScreenForWindow:
+//    The return of this method is an array of NSWindows. Each window that is
+//    returned will be added to the new virtual desktop after the animation is
+//    finished, but will not be a part of the animation itself.
+//  -window:startCustomAnimationToEnterFullScreenWithDuration:
+//    In this method, the window's delegate adds animations to the windows
+//    returned in the above method.
+//
+// The goal of this class is to mimic the default animation, but instead of
+// taking a snapshot of the final web content, it uses the live web content
+// during the animation.
+//
+// See https://code.google.com/p/chromium/issues/detail?id=414527#c22 and its
+// preceding comments for a more detailed description of the implementation,
+// and the reasoning behind the decisions made.
+//
+// Recommended usage:
+//  (Override method on NSWindow's delegate)
+//  - (NSArray*)customWindowsToEnterFullScreenForWindow:(NSWindow*)window {
+//    self.transition = [[[BrowserWindowEnterFullscreenTransition alloc]
+//        initWithWindow:window] autorelease];
+//    return [self.transition customWindowsToEnterFullScreen];
+//  }
+//
+//  (Override method on NSWindow's delegate)
+//  - (void)window:(NSWindow*)window
+//  startCustomAnimationToEnterFullScreenWithDuration:(NSTimeInterval)duration {
+//    [self.transition
+//        startCustomAnimationToEnterFullScreenWithDuration:duration];
+//  }
+//
+//  (Override method on NSWindow's delegate)
+//  - (void)windowDidEnterFullScreen:(NSNotification*)notification {
+//    self.transition = nil;
+//  }
+//
+//  (Override method on NSWindow)
+//  - (NSRect)constrainFrameRect:(NSRect)frame toScreen:(NSScreen*)screen {
+//    if (self.transition && ![self.transition shouldWindowBeConstrained])
+//      return frame;
+//    return [super constrainFrameRect:frame toScreen:screen];
+//  }
+
+@interface BrowserWindowEnterFullscreenTransition : NSObject
+
+// Designated initializer. |window| is the NSWindow that is going to be moved
+// into a fullscreen Space (virtual desktop), and resized to have the same size
+// as the screen. |window|'s root view must be layer backed.
+- (instancetype)initWithWindow:(NSWindow*)window;
+
+// Returns the windows to be used in the custom transition.
+//   - Takes a snapshot of the current window.
+//   - Makes a new snapshot window which shows the snapshot in the same
+//   location as the current window.
+//   - Adds the style mask NSFullScreenWindowMask to the current window.
+//   - Makes the current window transparent, and resizes the current window to
+//   be the same size as the screen.
+- (NSArray*)customWindowsToEnterFullScreen;
+
+// Begins the animations used for the custom fullscreen transition.
+//   - Animates the snapshot to the full size of the screen while fading it out.
+//   - Animates the current window from it's original location to its final
+//   location, while fading it in.
+// Note: The two animations are added to different layers in different windows.
+// There is no explicit logic to keep the two animations in sync. If this
+// proves to be a problem, the relevant layers should attempt to sync up their
+// time offsets with CACurrentMediaTime().
+- (void)startCustomAnimationToEnterFullScreenWithDuration:
+    (NSTimeInterval)duration;
+
+// When this method returns true, the NSWindow method
+// -constrainFrameRect:toScreen: must return the frame rect without
+// constraining it. The owner of the instance of this class is responsible for
+// hooking up this logic.
+- (BOOL)shouldWindowBeUnconstrained;
+
+@end
+
+#endif  // CHROME_BROWSER_UI_COCOA_BROWSER_WINDOW_FULLSCREEN_TRANSITION_H_