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first pass at hit testing #154

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first pass at hit testing #154

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5caa1c6
first pass at hit testing
cabanier Jun 5, 2020
96a0e97
Added XRSpace for hit test
cabanier Jun 6, 2020
fdbec8f
returned a sequence of hit results
cabanier Jun 7, 2020
5bc1e8d
Switched to XRSpace for hit result
cabanier Jun 8, 2020
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59 changes: 59 additions & 0 deletions webxrlayers-1.bs
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Expand Up @@ -36,6 +36,7 @@ spec: webxr-1;
type: dfn; text: active immersive session
type: dfn; text: type; for: XRReferenceSpace
type: dfn; text: session; for: XRSpace
type: dfn; text: native origin; for: XRSpace
type: dfn; text: XRLayer
type: dfn; text: XRReferenceSpace
type: dfn; text: type; for: XRReferenceSpace
Expand Down Expand Up @@ -1386,6 +1387,64 @@ when the [=XR Compositor=] can no longer reproject the layer.

The author SHOULD redraw the content of the layer at the next [=XR animation frame=]. The event must be of type {{XRLayerEvent}}.

Hit testing {#hittesting}
===========

XRLayerHitResult {#xrlayerhitresulttype}
----------------

<pre class="idl">
interface XRLayerHitResult {
readonly attribute XRCompositionLayer layer;
readonly attribute unsigned long x;
readonly attribute unsigned long y;
readonly attribute XRSpace hitSpace;
};
</pre>

The <dfn attribute for="XRLayerHitResult">layer</dfn> member returns what layer was hit.

The <dfn attribute for="XRLayerHitResult">x</dfn> and <dfn attribute for="XRLayerHitResult">y</dfn> member return the x and y position
where the layer was hit. This position is <code>0</code for the top/left position and <code>1</code> for the bottom/right position.

The <dfn attribute for="XRLayerHitResult">position</dfn> member returns the position in 3D space where the hit occured.

Finding hit tests {#finding-hit-tests}
-----------------

<pre class="idl">
[SecureContext, Exposed=Window] partial interface XRFrame {
sequence&lt;XRLayerHitResult&gt; findHitTest(XRSpace space, XRRigidTransform ray);
};
</pre>

<div class="algorithm" data-algorithm="findHitTestAlgo">

The <dfn method for="XRFrame">findHitTest(XRSpace |space|, XRRigidTransform |ray|)</dfn> method casts a ray into the
scene containing instances of {{XRCompositionLayer|XRCompositionLayers}}.

When this method is invoked, the user agent MUST run the following steps:
1. If [=this=] {{XRFrame/session}} was not created with "[=feature descriptor/layers=]" enabled, throw an {{NotSupportedError}} and abort these steps.
1. If [=this=]'s [=XRFrame/active=] boolean is <code>false</code>, throw an {{InvalidStateError}} and abort these steps.
1. Let |hitresults| be a new sequence created in the [=relevant realm=] of [=this=].
1. For each |layer| in [=this=] {{XRFrame/session}}'s {{XRRenderState/layers}}:
1. If |ray| using the orign |space| doesn't intersect |layer|, continue to the next entry.
1. Let |result| be a [=new=] instance of {{XRLayerHitResult}} in the [=relevant realm=] of [=this=].
1. Set |result|'s {{XRLayerHitResult/layer}} to the hit {{XRCompositionLayer}}.
1. Set |result|'s {{XRLayerHitResult/x}} and {{XRLayerHitResult/y}} to the position where the |ray| hit {XRLayerHitResult/layer}}.
1. Initialize |result|'s {{XRLayerHitResult/hitSpace}} as follows:
<dl class="switch">
<dt> If a previous hit was found with the same |layer| and [=this=], the user agent MAY:
<dd> Let |result|'s {{XRLayerHitResult/hitSpace}} be the same {{XRSpace}} object as returned by an earlier call with the same |layer| and [=this=].
<dt> Otherwise
<dd> Let |result|'s {{XRLayerHitResult/hitSpace}} be a [=new=] {{XRSpace}} in the [=relevant realm=] of [=this=].
</dl>
1. Set |result|'s {{XRLayerHitResult/hitSpace}} to an {{XRSpace}} that has a [=XRSpace/native origin=] to the pose that should be used to render the 3D position that was hit.
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This should be defined above, and it should be mentioned that the space is only valid during frames where the hit has happened.

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This should be defined above

What do you mean by "defined above"?

it should be mentioned that the space is only valid during frames where the hit has happened.

I looked how gripSpace is defined in the WebXR spec but I don't see where it mentions that it's only valid during the XRFrame.

1. Append |result| to |hitresults|.
1. Return |hitresults|.

</div>

WebXR Device API Integration {#webxrintegration}
============================

Expand Down