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diff --git a/examples/webengine/lifecycle/doc/src/lifecycle.qdoc b/examples/webengine/lifecycle/doc/src/lifecycle.qdoc deleted file mode 100644 index 4151d0597..000000000 --- a/examples/webengine/lifecycle/doc/src/lifecycle.qdoc +++ /dev/null @@ -1,167 +0,0 @@ -/**************************************************************************** -** -** Copyright (C) 2019 The Qt Company Ltd. -** Contact: https://www.qt.io/licensing/ -** -** This file is part of the documentation of the Qt Toolkit. -** -** $QT_BEGIN_LICENSE:FDL$ -** Commercial License Usage -** Licensees holding valid commercial Qt licenses may use this file in -** accordance with the commercial license agreement provided with the -** Software or, alternatively, in accordance with the terms contained in -** a written agreement between you and The Qt Company. For licensing terms -** and conditions see https://www.qt.io/terms-conditions. For further -** information use the contact form at https://www.qt.io/contact-us. -** -** GNU Free Documentation License Usage -** Alternatively, this file may be used under the terms of the GNU Free -** Documentation License version 1.3 as published by the Free Software -** Foundation and appearing in the file included in the packaging of -** this file. Please review the following information to ensure -** the GNU Free Documentation License version 1.3 requirements -** will be met: https://www.gnu.org/licenses/fdl-1.3.html. -** $QT_END_LICENSE$ -** -****************************************************************************/ - -/*! - \example webengine/lifecycle - \title WebEngine Lifecycle Example - \ingroup webengine-examples - \brief Freezes and discards background tabs to reduce CPU and memory usage. - - \image lifecycle.png - - \e {WebEngine Lifecycle Example} demonstrates how the \l - {WebEngineView::}{lifecycleState} and \l {WebEngineView::}{recommendedState} - properties of the \l {WebEngineView} can be used to reduce the CPU and - memory usage of background tabs in a tabbed browser. - - \include examples-run.qdocinc - - \section1 UI Elements of the Example - - The example uses \l {Qt Quick Controls 2} to implement a traditional tabbed - browser in the \l {Material Style} (dark variant). The main application - window (\c {WebBrowser.qml}) is divided into a header bar at the top and a - main viewing area filling the rest of the window. The header contains the - tab bar (\c {WebTabBar.qml}) with one button per tab (\c - {WebTabButton.qml}). The main area consists of a stack of tabs (\c - {WebTabStack.qml} and \c {WebTab.qml}). Each tab in turn has a tool bar at - the top and a \l {WebEngineView} for displaying web pages. Finally, the main - window also has a \l {Drawer} for changing settings. The drawer can be - opened by clicking the "⋮" button on the tool bar. - - \section1 Overview of Lifecycle States - - Each \l {WebEngineView} item can be in one of three \e {lifecycle states}: - active, frozen, or discarded. These states, like the sleep states of a CPU, - control the resource usage of web views. - - The \e {active} state is the normal, unrestricted state of a web view. All - visible web views are always in the active state, as are all web views that - have not yet finished loading. Only invisible, idle web views can be - transitioned to other lifecycle states. - - The \e {frozen} state is a low CPU usage state. In this state, most HTML - task sources are suspended (frozen) and, as a result, most DOM event - processing and JavaScript execution will also be suspended. The web view - must be invisible in order to be frozen as rendering is not possible in this - state. - - The \e {discarded} state is an extreme resource-saving state. In this state, - the browsing context of the web view will be discarded and the corresponding - renderer subprocess shut down. CPU and memory usage in this state is reduced - virtually to zero. On exiting this state the web page will be automatically - reloaded. The process of entering and exiting the discarded state is similar - to serializing the browsing history of the web view and destroying the view, - then creating a new view and restoring its history. - - See also \l {WebEngineView::LifecycleState}. The equivalent in the Widgets - API is \l {QWebEnginePage::LifecycleState}. - - \section2 The \c {lifecycleState} and \c {recommendedState} Properties - - The \l {WebEngineView::}{lifecycleState} property of the \l {WebEngineView} - type is a read-write property that controls the current lifecycle state of - the web view. This property is designed to place as few restrictions as - possible on what states can be transitioned to. For example, it is allowed - to freeze a web view that is currently playing music in the background, - stopping the music. In order to implement a less aggressive resource-saving - strategy that avoids interrupting user-visible background activity, the \l - {WebEngineView::} {recommendedState} property must be used. - - The \l {WebEngineView::}{recommendedState} property of the \l - {WebEngineView} type is a read-only property that calculates a safe limit on - the \l {WebEngineView::}{lifecycleState} property, taking into account the - current activity of the web view. So, in the example of a web view playing - music in the background, the recommended state will be \c {Active} since a - more aggressive state would stop the music. If the application wants to - avoid interrupting background activity, then it should avoid putting the web - view into a more aggressively resource-saving lifecycle state than what's - given by \l {WebEngineView::}{recommendedState}. - - See also \l {WebEngineView::lifecycleState} and \l - {WebEngineView::recommendedState}. The equivalents in the Widgets API are \l - {QWebEnginePage::lifecycleState} and \l {QWebEnginePage::recommendedState}. - - \section2 The Page Lifecycle API - - The \l {WebEngineView::}{lifecycleState} property is connected to the \l - {https://wicg.github.io/page-lifecycle/spec.html}{Page Lifecycle API}, a - work-in-progress extension to the HTML standard that specifies two new DOM - events, \c {freeze} and \c {resume}, and adds a new \c - {Document.wasDiscarded} boolean property. The \c {freeze} and \c {resume} - events are fired when transitioning from the \c {Active} to the \c {Frozen - state}, and vice-versa. The \c {Document.wasDiscarded} property is set to \c - {true} when transition from the \c {Discarded} state to the \c {Active} - state. - - \section1 Lifecycle States in the Example - - The example implements two ways of changing the lifecycle state: manual and - automatic. The manual way uses the \l {WebEngineView::}{lifecycleState} - property directly to change the web view lifecycle state, while the - automatic way is timer-based and also takes into account the \l - {WebEngineView::}{recommendedState}. - - The tab titles in the tab bar are color coded with frozen tabs shown in blue - and discarded in red. - - \section2 Manual Lifecycle Control - - \image lifecycle-manual.png - - Manual control is provided by context menus on the tab bar buttons (\c - {WebTabButton.qml}). The menu has three radio buttons, one for each - lifecycle state, with the current state checked. Some buttons may be - disabled, either because they represent illegal state transitions (for - example, a \c {Discarded} view cannot directly transition to the \c {Frozen} - state), or because other preconditions are not fulfilled (for example, a - visible view can only be in the \c {Active} state). - - \section2 Automatic Lifecycle Control - - \image lifecycle-automatic.png - - Automatic control is implemented with a \l {Timer} in the \c {WebTab} - component (\c {WebTab.qml}). The timer is started whenever the \l - {WebEngineView::}{lifecycleState} of the web view does not match it's \l - {WebEngineView::}{recommendedState}. Once the timer fires, the view's - lifecycle state is set to the recommended state. - - The time delay is used to avoid changing the lifecycle state too quickly - when the user is switching between tabs. The freezing and discarding delays - can be changed in the settings drawer accessed through the "⋮" button on the - tool bar. - - This is a rather simple algorithm for automatic lifecycle control, however - more sophisticated algorithms could also be conceived and implemented on the - basis of the \l {WebEngineView::}{lifecycleState} property. For example, the - Chromium browser experimentally uses a pretrained deep neural network to - predict the next tab activation time by the user, essentially ranking tabs - based on how interesting they are to the user. Implementing such an - algorithm is left as an exercise to the reader for now. - -*/ |