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Rework the 'Connect to Sensor' abstract operation #300

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Oct 4, 2017
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Rework the 'Connect to Sensor' abstract operation #300

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47 changes: 20 additions & 27 deletions index.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -599,8 +599,13 @@ for each [=sensor types|type=]
simply by instantiating the corresponding {{Sensor}} subclass.

Indeed, without specific information identifying a particular [=device sensor|sensor=]
of a given [=sensor type|type=],
the <dfn export>default sensor</dfn> is chosen.
of a given [=sensor type|type=], the <dfn export>default sensor</dfn> is chosen by the
user agent.

If the underlying platform provides an interface to find the [=default sensor=],
the user agent must choose the sensor offered by the platform, otherwise the user agent
itself defines which of the [=device sensor|sensors=] present on the device is
the [=default sensor=].

<div class="example">
Listening to the default accelerometer changes:
Expand Down Expand Up @@ -704,10 +709,6 @@ whose [=inherited interfaces=] contains {{Sensor}}.

A [=sensor type=] has a [=ordered set|set=] of <dfn export>associated sensors</dfn>.

If a [=sensor type=] has more than one [=platform sensor=],
it must have a set of associated <dfn export>identifying parameters</dfn>
to select the right [=platform sensor=] to associate to each new {{Sensor}} objects.

A [=sensor type=] may have a [=default sensor=].

A [=sensor type=] has an associated {{PermissionName}}.
Expand Down Expand Up @@ -964,14 +965,6 @@ with the internal slots described in the following table:
notified after a new [=sensor reading=] was reported.
It is initially false.</td>
</tr>
<tr>
<td><dfn attribute for=Sensor>\[[identifyingParameters]]</dfn></td>
<td>
A [=sensor type=]-specific group of [=dictionary members=]
used to select the correct [=platform sensor=]
to associate to this {{Sensor}} object.
</td>
</tr>
</tbody>
</table>

Expand Down Expand Up @@ -1016,7 +1009,8 @@ and "timestamp" as arguments.
or "activated", then return.
1. Set |sensor_instance|.{{[[state]]}} to "activating".
1. Run these sub-steps [=in parallel=]:
1. let |connected| be the result of invoking [=connect to sensor=].
1. let |connected| be the result of invoking [=connect to sensor=] with |sensor_instance|
as argument.
1. If |connected| is false, then
1. Let |e| be the result of [=created|creating=] a
"{{NotReadableError!!exception}}" {{DOMException}}.
Expand Down Expand Up @@ -1143,8 +1137,6 @@ Gets the {{Error}} object passed to {{SensorErrorEventInit}}.
Note: there is not guarantee that the requested |options|.{{frequency!!dict-member}}
can be respected. The actual [=sampling frequency=] can be calculated using
{{Sensor}} {{Sensor/timestamp!!attribute}} attributes.
1. If [=identifying parameters=] in |options| are set, then:
1. Set |sensor_instance|.{{[[identifyingParameters]]}} to [=identifying parameters=].
1. Set |sensor_instance|.{{[[state]]}} to "idle".
1. Return |sensor_instance|.
</div>
Expand All @@ -1160,16 +1152,18 @@ Gets the {{Error}} object passed to {{SensorErrorEventInit}}.
:: True if sensor instance was associated with a [=platform sensor=],
false otherwise.

1. If |sensor_instance|.{{[[identifyingParameters]]}} is set and
|sensor_instance|.{{[[identifyingParameters]]}} allows
a unique [=platform sensor=] to be identified, then:
1. let |sensor| be that [=platform sensor=],
1. associate |sensor_instance| with |sensor|.
1. Return true.
1. If the [=sensor type=] of |sensor_instance| has an associated [=default sensor=]
and there is a corresponding [=platform sensor=] on the device, then
1. associate |sensor_instance| with [=default sensor=].
1. Let |type| be the [=sensor type=] of |sensor_instance|.
1. If the device has a single [=device sensor=] which can provide [=sensor readings|readings=]
for |type|, then
1. Associate |sensor_instance| with a [=platform sensor=] corresponding
to this [=device sensor=].
1. Return true.
1. If the device has multiple [=device sensors=] which can provide [=sensor readings|readings=]
for |type|, then
1. If |type| has an associated [=default sensor=], then
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If platform does not have concept of default sensor, false would be returned, is that expected?

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but that's not a platform concept, default sensor is defined in an extension API, e.g. here https://www.w3.org/TR/accelerometer/#model, so if a device has multiple accelerometers, the UA will assume one of them to be the default.

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@alexshalamov alexshalamov Oct 4, 2017 •
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thanks, additional text addresses my concern about vague definition of default sensor.

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Outside this change in Sensor.start(), where you invoke this connect to sensor abstract operation, you should change:

let connected be the result of invoking connect to sensor.

To

let connected be the result of invoking connect to sensor with sensor_instance as argument.

Might be a separate patch, or could be rolled into this one since related.

1. Associate |sensor_instance| with a [=platform sensor=] corresponding
to [=default sensor=].
1. Return true.
1. Return false.
</div>

Expand Down Expand Up @@ -1528,7 +1522,6 @@ for each [=sensor types=]:
For [=sensor types=] where multiple [=device sensor|sensors=] are common,
[=extension specifications=] may choose not to define a [=default sensor=],
especially when doing so would not make sense.
- A set of [=identifying parameters=]. TODO: replace that by an abstract operation.

<h3 id="permission-api">Extending the Permission API</h3>

Expand Down
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