0049-touch-cancellation.md

Gesture cancellation on video streaming

• Proposal: SDL-0049
• Author: Masato Ogawa
• Status: Accepted
• Impacted Platforms: [Core / iOS / Android / RPC]

Introduction

This proposal defines a gesture cancellation event to prevent false gesture recognition during an interrupted video stream.

Motivation

During operation with an SDL application supporting video streaming, a native dialog such as incoming-call may interrupt. If touch events before and after a screen interruption are evaluated as one gesture, an unexpected gesture may be detected.

Proposed solution

HMI notifies gesture cancellation by OnTouchEvent method of UI component.

Detailed design

Additions to Mobile_API

 <enum name="TouchType">
   <element name="BEGIN"/>
   <element name="MOVE"/>
   <element name="END"/>
+  <element name="CANCEL"/>
 </enum>

Additions to HMI_API

 <enum name="TouchType">
   <element name="BEGIN"/>
   <element name="MOVE"/>
   <element name="END"/>
+  <element name="CANCEL"/>
 </enum>

HMI notifies with JSON as below. It passes through Core and is passed to Application. In the case of multi-touch, it is necessary to notify each ID.

{
  "jsonrpc" : "2.0",
  "method" : "UI.OnTouchEvent",
  "params" :
  {
    "type" : "CANCEL",
    "event" : [
                {
                  "id":0,
                  "ts":[49013],
                  "c":[{"x":323,"y":259}],
                }
              ]
  }
}

Potential downsides

1. Can it be implemented with currently defined values?

Yes, we can treat TouchType::BEGIN during TouchType::MOVE as a cancellation. However, to avoid misunderstanding, it's good to define a single event rather than defining a sequence. And general mobile OS has an event like this.

Impact on existing code

This change is only adding TouchType's enum value. It does not stop compilation and does not change the current behavior.

Alternatives considered

If TouchType::BEGIN is received during TouchType::MOVE, the application cancels gesture recognition.