| // Copyright 2019 The Fuchsia Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| library fuchsia.ui.views; |
| |
| /// A View is an interface that a component implements to offer Scenic view(s) |
| /// to its clients. |
| /// |
| /// A Scenic view contains a tree of Scenic graph nodes which is used to render |
| /// a graphical user interface, such as a module, shell, or on-screen keyboard. |
| /// Other Scenic views can be embedded within this tree of nodes. This creates |
| /// a scene graph describing the UI of the entire system, rooted at the |
| /// top-most view. Different processes can contribute branches to the scene |
| /// graph, and their content will be rendered together in a shared space. |
| /// |
| /// # Offering a View |
| /// |
| /// A component that wishes to offer a |View| can do so in one of two ways: |
| /// |
| /// 1. Expose a |View| interface as a service. This is usually done by components |
| /// that provide a single view, or have a clearly defined "main" view. |
| /// In this case, the component may obtain relevant properties for configuring |
| /// the view using services that may be available in its namespace, such as: |
| /// - |fuchsia.intl.PropertyProvider| |
| /// - |fuchsia.accessibility.PropertyProvider| |
| /// |
| /// 2. Offer a domain-specific interface that provides |View|s using a |
| /// `request<View>` parameter. In this case, the component may obtain relevant |
| /// properties for configuring the view using services that may be provided by its |
| /// client as part of the request. |
| /// |
| /// For example, an encyclopedia component might offer a method to expose article views: |
| /// |
| /// GetArticleView(string article_id, |
| /// fuchsia.intl.PropertyProvider intl_properties, |
| /// fuchsia.accessibility.PropertyProvider accessibility_properties, |
| /// request<View> view_request); |
| /// |
| /// This latter case is probably less common, as controlling domain-specific |
| /// views tends to be the job of the component that creates them. |
| /// |
| /// # Presenting a View |
| /// |
| /// A client of the |View| interface will: |
| /// |
| /// 1. Launch (or bind to) the component that provides the interface. |
| /// 2. Connect to the component's |View| interface. |
| /// 3. Call |Present()| to give the |View| an attachment point into the scene graph |
| /// via the |view_token|. Subsequent calls to |Present()| will generate an error |
| /// and cause the connection to be closed. |
| /// |
| /// When the client no longer needs the View, it should disconnect from the |
| /// interface. |
| /// |
| /// NOTE: The client owns the |View| instance and must retain it for the |
| /// lifetime of the UI that it displays. If the |View| instance is destroyed, |
| /// the connection will be dropped and all UI content will be destroyed. |
| /// |
| /// # Implementing a View |
| /// |
| /// On the implementation side, a component that exposes the |View| interface |
| /// has the following responsibilities: |
| /// |
| /// * When |Present()| is called, create a root for the |View|'s content in the |
| /// Scenic scene graph by passing the provided |view_token|. |
| /// * Provide graphical content for the view and attach it to the root. |
| /// * Adjust the appearance and/or contents of the view's content based on |
| /// relevant internationalization and/or accessibility properties as described |
| /// above. |
| /// * Handle user interface events such as touches, key presses, and |
| /// |fuchsia.ui.gfx.ViewProperty| changes using other Scenic interfaces such |
| /// as |fuchsia.ui.Scenic| and |fuchsia.ui.SessionListener|. |
| /// |
| /// See also: |fuchsia.intl.PropertyProvider|, |fuchsia.accessibility.PropertyProvider|. |
| /// |
| /// TODO(SCN-1198): Migrate all implementations of |ViewProvider| to use |View|. |
| [Discoverable] |
| protocol View { |
| /// DEPRECATED |
| [Transitional] |
| Present(ViewToken view_token, ViewConfig initial_config); |
| |
| /// Provides the View with an attachment point to Scenic's scene graph. |
| /// |
| /// When |Present()| is called the View's implementation should create a |
| /// View resource within Scenic by providing it with the |view_token| (using |
| /// a |fuchsia.ui.gfx.CreateResourceCmd| and |fuchsia.ui.gfx.ViewArgs|). |
| /// |
| /// Then the implementation should attach its graphical content to the |
| /// newly-created View resource using a |fuchsia.ui.gfx.AddChildCmd|. |
| /// |
| /// If the implementation already owns a View resource (because |Present()| |
| /// had already been called before), then it should terminate the connection |
| /// with an error. |
| /// |
| /// TODO(SCN-1271): Allow re-parenting |View|s with a new |Present()| call. |
| /// TODO(SCN-1343): Rename to |Present()|. |
| [Transitional] |
| Present2(ViewToken view_token); |
| |
| /// DEPRECATED |
| [Transitional] |
| SetConfig(ViewConfig config); |
| }; |
| |
| /// A ViewRef is a handle to a kernel object which identifies a unique View |
| /// across the system. Two ViewRefs to the same View have the same KOID. |
| /// |
| /// Clients use a ViewRef to identify a View, to validate a View, and to |
| /// receive a View invalidation signal. |
| /// |
| /// As part of View creation, the client creates a linked |
| /// ViewRef/ViewRefControl pair and hands the pair to Scenic (ViewRefControl is |
| /// described below). The client must remove the ViewRef's signal |
| /// capabilities; otherwise the View is not created. |
| /// |
| /// The client may freely clone its ViewRef and share it, even before sending |
| /// it to Scenic. |
| /// |
| /// Example 1. Accessibility accepts a ViewRef from a client to group the |
| /// semantic nodes, and semantic operations, associated with a client's View. |
| /// It must validate a client's ViewRef with Scenic. |
| /// |
| /// Example 2. We use ViewRefs to create a FocusChain, which identifies Views |
| /// considered as "in-focus" down the View hierarchy. When a View is destroyed, |
| /// Scenic signals to all FocusChain holders that the ViewRef is now invalid. |
| struct ViewRef { |
| handle<eventpair> reference; |
| }; |
| |
| /// A ViewRefControl is the peer to a ViewRef. Their |reference|s are linked. |
| /// |
| /// Like ViewRef, a ViewRefControl is a typed handle to an eventpair. Unlike |
| /// ViewRef, a ViewRefControl's handle is unique. Scenic uses this property |
| /// when it ties a ViewRefControl to a View, arranged to share fate. When a |
| /// View is destroyed, the associated destruction of its ViewRefControl |
| /// triggers an automatic ZX_ERR_PEER_CLOSED signal sent to all ViewRef |
| /// holders; hence ViewRef holders may track View lifetime. |
| /// |
| /// As part of View creation, the client creates a linked |
| /// ViewRef/ViewRefControl pair and hands the pair to Scenic (ViewRef is |
| /// described above). The client must not clone the ViewRefControl. It must |
| /// not remove or modify the ViewRefControl's capabilities; otherwise the View |
| /// is not created. |
| struct ViewRefControl { |
| handle<eventpair> reference; |
| }; |