Enum TouchSourceRequest

pub enum TouchSourceRequest {
    Watch {
        responses: Vec<TouchResponse>,
        responder: TouchSourceWatchResponder,
    },
    UpdateResponse {
        interaction: TouchInteractionId,
        response: TouchResponse,
        responder: TouchSourceUpdateResponseResponder,
    },
}

A method for a client to receive touch events and respond in a global gesture disambiguation protocol.

The position of a touch event is defined in the context of a viewport, situated in the view. The dimensions of the view and viewport, and their spatial relationship (defined with a transform matrix), are supplied synchronously in a |ViewParameter| table. A view may retrieve a pointer’s position in its local coordinate system by applying the viewport-to-view transform matrix.

The viewport is embedded in an independent and stable coordinate system, suitable for interpreting touch events in a scale-independent manner; a swipe will be observed at a constant scale, even under effects such as magnification or panning. However, other effects, such as enlargening the view’s clip bounds, may trigger a change in the viewport extents.

Variants

Watch

A method for a client to receive touch pointer events.

This call is formulated as a “hanging get” pattern: the client asks for a set of recent events, and receives them via the callback. This pull-based approach ensures that clients consume events at their own pace; events don’t clog up the channel in an unbounded manner.

Flow control. The caller is allowed at most one in-flight |Watch| call at a time; it is a logical error to have concurrent calls to |Watch|. Non-compliance results in channel closure.

Client pacing. The server will dispatch events to the caller on a FIFO, lossless, best-effort basis, but the caller must allocate enough time to keep up with new events. An unresponsive client may be categorized as “App Not Responding” and targeted for channel closure.

Responses. The gesture disambiguation scheme relies on the server receiving a |TouchResponse| for each |TouchEvent|.|TouchPointerSample|; non-sample events should return an empty |TouchResponse| table to the server. Responses for previous events are fed to the server on the next call of |Watch| [1]. Each element in the |responses| vector is interpreted as the pairwise response to the event in the previous |events| vector; the vector lengths must match. Note that the client’s contract to respond to events starts as soon as it registers its endpoint with scenic, NOT when it first calls Watch().

Initial response. The first call to |Watch| must be an empty vector.

Event times. The timestamps on each event in the event vector are not guaranteed monotonic; touch events from different devices may be injected into Scenic at different times. Generally, events from a single device are expected to have monotonically increasing timestamps.

View parameters. Occasionally, changes in view or viewport require notifying the client. If a |TouchEvent| carries |ViewParameters|, these parameters apply to successive |TouchPointerSample|s until the next |ViewParameters|.

[1] The hanging get pattern enables straightforward API evolution, but unfortunately does not admit an idiomatic matching of response to event.

Fields

responses: Vec<TouchResponse>

responder: TouchSourceWatchResponder

UpdateResponse

The gesture protocol allows a client to enact a “hold” on an open interaction of touch events; it prevents resolution of interaction ownership, even after the interaction closes. This method updates the client’s previous “hold” by replacing it with a response that allows ownership resolution to proceed.

See |TouchInteractionId| for how a stream is structured into interactions.

Flow control. The caller is allowed at most one |UpdateResponse| call per interaction, and it must be on a closed interaction. It is a logical error to call |UpdateResponse| when a normal response is possible with the |Watch| call.

Validity. This TouchResponse must not be another “hold” response, and the overwritten response is expected to be a “hold” response.

Fields

interaction: TouchInteractionId

response: TouchResponse

responder: TouchSourceUpdateResponseResponder

Implementations

impl TouchSourceRequest

pub fn into_watch( self, ) -> Option<(Vec<TouchResponse>, TouchSourceWatchResponder)>

pub fn into_update_response( self, ) -> Option<(TouchInteractionId, TouchResponse, TouchSourceUpdateResponseResponder)>

pub fn method_name(&self) -> &'static str

Name of the method defined in FIDL

Trait Implementations

impl Debug for TouchSourceRequest

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.