sdk/fidl/fuchsia.ui.composition.internal/screen_capture.fidl

// Copyright 2022 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.composition.internal;

using fuchsia.ui.composition;
using fuchsia.math;
using zx;

/// Possible errors of the ScreenCapture protocol.
type ScreenCaptureError = flexible enum {
    /// One or more of the arguments was missing.
    MISSING_ARGS = 1;
    /// One or more of the arguments was not valid.
    INVALID_ARGS = 2;
    /// Indicates that the client has sent an overwritten hanging get.
    BAD_HANGING_GET = 3;
};

/// Rotation applied to the image.
/// For example, if the display is rotated 90 degrees according to its
/// `display_info` config file, the image can be captured as if the display
/// is not rotated (0 degrees) by applying CW_270_DEGREES.
type ScreenCaptureRotation = strict enum {
    CW_0_DEGREES = 0;
    CW_90_DEGREES = 1;
    CW_180_DEGREES = 2;
    CW_270_DEGREES = 3;
};

/// Fields required to set up a ScreenCapture protocol in the [`Configure`]
/// call. Notice some fields are optional.
type ScreenCaptureConfig = resource table {
    /// The import token referencing a BufferCollection registered with the
    /// Allocator.
    /// Required.
    1: import_token fuchsia.ui.composition.BufferCollectionImportToken;

    /// The size of the image in pixels: width and height.
    /// This should be the width and height calculated after the
    /// rotation that will be applied.
    /// Required.
    2: image_size fuchsia.math.SizeU;

    /// The rotation applied to the stream of images.
    /// Defaults to CW_0_DEGREES (no rotation).
    /// Optional.
    3: image_rotation ScreenCaptureRotation;
};

/// Return fields of the [`GetNextFrame`] call. These fields hold the
/// frame’s information on buffer location, timing, and a way to release
/// after using it. All fields will be returned by the server.
type FrameInfo = resource table {
    /// The index of the VMO where the requested frame has been rendered
    /// in the buffer collection.
    1: buffer_index uint32;

    /// The time that the buffer was populated with the frame.
    2: capture_timestamp zx.time;

    /// The release token for |buffer_index|. The client drops the eventpair
    /// to signal to the server that |buffer_index| is free for writing.
    /// If the eventpair is not dropped, then in the future calls to
    /// [`GetNextFrame`], if there are no available buffers, the server will
    /// wait until the client frees up a past buffer. If the client was holding
    /// on to all buffers in the buffer collection and then
    /// releases a buffer while hanging, the server will immediately return the
    /// latest frame.
    3: buffer_release_token zx.handle:EVENTPAIR;
};

/// Provides a low-level streaming API for clients to use.
/// ScreenCapture clients should familiarize themselves with the
/// [`fuchsia.sysmem/BufferCollection`] and
/// [`fuchsia.ui.composition/Allocator`] protocols as those are necessary to
/// create the BufferCollections and images ScreenCapture uses.
@discoverable
protocol ScreenCapture {
    /// Clients should first use the ['fuchsia.ui.composition/Allocator']
    /// protocol to register a BufferCollection.
    ///
    /// Similarly, the clients are responsible for specifying a buffer big
    /// enough for the image. If the buffer is too small, an
    /// attempt will be made to render the image, however, it will not be
    /// guaranteed to contain the complete image.
    Configure(ScreenCaptureConfig) -> () error ScreenCaptureError;

    /// [`GetNextFrame`] returns the latest unseen-by-the-client frame as soon
    /// as possible. On the first call to [`GetNextFrame`] and any subsequent
    /// calls that have not recieved the previous expected requested frame,
    /// [`GetNextFrame`] will return immediately with the last frame to be
    /// rendered. If the client had requested the previous frame, the server
    /// will wait until the next frame is produced to return.
    ///
    /// After the client finishes processing the returned buffer, they should
    /// drop the eventpair to signal to the server that the buffer can be
    /// re-used.
    ///
    /// It is invalid to call [`GetNextFrame`] while a previous call is still
    /// pending. Doing so will return a BAD_HANGING_GET error and cause the
    /// channel to close.
    GetNextFrame() -> (FrameInfo) error ScreenCaptureError;
};