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Split input sources into primary/auxiliary #929

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merged 7 commits into from
Jan 9, 2020
Merged

Split input sources into primary/auxiliary #929

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2bca34a
Split input sources into primary/auxiliary
klausw Nov 20, 2019
9881abd
Clarify that transient action handling replaces primary actions
klausw Nov 20, 2019
bf439b4
Remove auxiliary input source and tracker example
klausw Dec 13, 2019
c43c01c
Revert "Remove auxiliary input source and tracker example"
klausw Dec 16, 2019
8402d50
Auxiliary input: remove tracker example, mention transient input source
klausw Dec 16, 2019
0527c57
Manish's grammar fix
klausw Dec 16, 2019
a1723b3
Define "auxiliary action" and refer to that in description
klausw Dec 19, 2019
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22 changes: 12 additions & 10 deletions index.bs
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Expand Up @@ -1544,7 +1544,9 @@ Similarly, the Valve Index controller is backwards compatible with the HTC Vive

Note: {{XRInputSource}}s in an {{XRSession}}'s {{XRSession/inputSources}} array are "live". As such values within them are updated in-place. This means that it doesn't work to save a reference to an {{XRInputSource}}'s attribute on one frame and compare it to the same attribute in a subsequent frame to test for state changes, because they will be the same object. Therefore developers that wish to compare input state from frame to frame should copy the content of the state in question.

Each [=XR input source=] MUST define a <dfn>primary action</dfn>. The [=primary action=] is a platform-specific action that, when engaged, produces {{XRSession/selectstart}}, {{XRSession/selectend}}, and {{XRSession/select}} events. Examples of possible [=primary action=]s are pressing a trigger, touchpad, or button, speaking a command, or making a hand gesture. If the platform guidelines define a recommended primary input then it should be used as the [=primary action=], otherwise the user agent is free to select one.
An [=XR input source=] is a <dfn>primary input source</dfn> if it supports a <dfn>primary action</dfn>. The [=primary action=] is a platform-specific action that, when engaged, produces {{XRSession/selectstart}}, {{XRSession/selectend}}, and {{XRSession/select}} events. Examples of possible [=primary action=]s are pressing a trigger, touchpad, or button, speaking a command, or making a hand gesture. If the platform guidelines define a recommended primary input then it should be used as the [=primary action=], otherwise the user agent is free to select one. The device MUST support at least one [=primary input source=].

An [=XR input source=] is a <dfn>auxiliary input source</dfn> if it does not support a [=primary action=], for example [=transient input sources=] associated with secondary screen touches on a multitouch device.
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Suggested change
An [=XR input source=] is a <dfn>auxiliary input source</dfn> if it does not support a [=primary action=], for example [=transient input sources=] associated with secondary screen touches on a multitouch device.
An [=XR input source=] is an <dfn>auxiliary input source</dfn> if it does not support a [=primary action=], for example [=transient input sources=] associated with secondary screen touches on a multitouch device.

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Done in 0527c57


<div class="algorithm" data-algorithm="on-input-start">

Expand Down Expand Up @@ -1611,43 +1613,43 @@ When an [=XR input source=] |source| for {{XRSession}} |session| has its [=prima
Transient input {#transient-input}
---------------

Some [=/XR device=]s may support <dfn>transient input sources</dfn>, where the [=XR input source=] is only meaningful while performing its [=primary action=]. An example would be mouse, touch, or stylus input against an {{XRSessionMode/"inline"}} {{XRSession}}, which MUST produce a transient {{XRInputSource}} with a {{targetRayMode}} set to {{screen}}. [=Transient input sources=] are only present in the session's [=list of active XR input sources=] for the duration of the the {{selectstart}}, {{select}}, and {{selectend}} event sequence.
Some [=/XR device=]s may support <dfn>transient input sources</dfn>, where the [=XR input source=] is only meaningful while performing a <dfn>transient action</dfn>, either the [=primary action=] for a [=primary input source=], or a device-specific action for an [=auxiliary input source=]. An example would be mouse, touch, or stylus input against an {{XRSessionMode/"inline"}} {{XRSession}}, which MUST produce a transient {{XRInputSource}} with a {{targetRayMode}} set to {{screen}}, treated as a [=primary action=] for the [[POINTEREVENTS#dfn-primary-pointer]], and as a non-primary [=transient action=] for a non-primary pointer. [=Transient input sources=] are only present in the session's [=list of active XR input sources=] for the duration of the [=transient action=].
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You've deleted the definition of auxiliary input source but still refer to it here. We should still be defining it somewhere.

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Sorry about the mismatch. I've reverted the deletion, and made a new change that basically just updates the example text to remove the tracker reference and links to transient input sources for secondary screen touches.

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I've made a small change to this section in commit a1723b3, using the new term "auxiliary action" to refer to a device-specific non-primary action. It was too easy to misintepret "non-primary [=transient action=]" as implying that all transient actions are non-primary, but that's not the case - they include both types.


[=Transient input sources=] follow a slightly different sequence when firing [=primary action=] events:
[=Transient input sources=] follow the following sequence when handling [=transient actions=] instead of the algorithms for non-transient [=primary actions=]:

<div class="algorithm" data-algorithm="on-transient-input-start">

When a [=transient input source=] |source| for {{XRSession}} |session| begins its [=primary action=] the UA MUST run the following steps:
When a [=transient input source=] |source| for {{XRSession}} |session| begins its [=transient action=] the UA MUST run the following steps:
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The text below seems to imply that transient actions can also be primary actions, but this means that select events would be fired twice since this line no longer "replaces" the primary action spec text the way it used to.

Is there ever a case for a non-primary transient action?

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I've rephrased it in 9d55efa. I wasn't aware that this was a replacement, that's rather subtle...

An example for a non-primary transient action would be adding additional fingers to a multitouch screen, these would create transient input sources and corresponding inputsourceschange events, but no select{,start,end} events, similar to how non-primary pointer events don't generate compatibility mouse events. I had updated the example in the previous paragraph to cover that.

As a side note, one additional reason for introducing this distinction is that I'm currently working on the DOM Overlay draft spec, where it would be useful to have a concept of transient sources that don't necessarily trigger XR select events, i.e. because they were handled as a DOM event. That's beyond the scope of this PR, and we can revisit this issue as part of that discussion, but I thought that the concept of non-primary transient sources would also be useful on its own.


1. Let |frame| be a new {{XRFrame}} with {{XRFrame/session}} |session| for the time the action occurred.
1. [=Queue a task=] to perform the following steps:
1. Fire any <code>"pointerdown"</code> events produced by the [=XR input source=]'s action, if necessary.
1. [=add input source|Add the XR input source=] to the [=list of active XR input sources=].
1. [=Fire an input source event=] with name {{selectstart!!event}}, frame |frame|, and source |source|.
1. If the [=transient action=] is a [=primary action=], [=fire an input source event=] with name {{selectstart!!event}}, frame |frame|, and source |source|.

</div>

<div class="algorithm" data-algorithm="on-transient-input-end">

When a [=transient input source=] |source| for {{XRSession}} |session| ends its [=primary action=] the UA MUST run the following steps:
When a [=transient input source=] |source| for {{XRSession}} |session| ends its [=transient action=] the UA MUST run the following steps:

1. Let |frame| be a new {{XRFrame}} with {{XRFrame/session}} |session| for the time the action occurred.
1. [=Queue a task=] to perform the following steps:
1. [=Fire an input source event=] with name {{select!!event}}, frame |frame|, and source |source|.
1. If the [=transient action=] is a [=primary action=], [=fire an input source event=] with name {{select!!event}}, frame |frame|, and source |source|.
1. Fire any <code>"click"</code> events produced by the [=XR input source=]'s action, if necessary.
1. [=Fire an input source event=] with name {{selectend!!event}}, frame |frame|, and source |source|.
1. If the [=transient action=] is a [=primary action=], [=fire an input source event=] with name {{selectend!!event}}, frame |frame|, and source |source|.
1. [=remove input source|Remove the XR input source=] from the [=list of active XR input sources=].
1. Fire any <code>"pointerup"</code> events produced by the [=XR input source=]'s action, if necessary.

</div>

<div class="algorithm" data-algorithm="on-transient-input-cancelled">

When a [=transient input source=] |source| for {{XRSession}} |session| has its [=primary action=] cancelled the UA MUST run the following steps:
When a [=transient input source=] |source| for {{XRSession}} |session| has its [=transient action=] cancelled the UA MUST run the following steps:

1. Let |frame| be a new {{XRFrame}} with {{XRFrame/session}} |session| for the time the action occurred.
1. [=Queue a task=] to perform the following steps:
1. [=Fire an input source event=] with name {{selectend!!event}}, frame |frame|, and source |source|.
1. If the [=transient action=] is a [=primary action=], [=fire an input source event=] with name {{selectend!!event}}, frame |frame|, and source |source|.
1. [=remove input source|Remove the XR input source=] from the [=list of active XR input sources=].
1. Fire any <code>"pointerup"</code> events produced by the [=XR input source=]'s action, if necessary.

Expand Down