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Single-canvas inline, drop XRPresentationContext #656

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Merged
merged 10 commits into from
Jun 13, 2019
Merged

Single-canvas inline, drop XRPresentationContext #656

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b7a1a8f
Single-canvas inline, drop XRPresentationContext
toji May 17, 2019
771b48a
Updated the explainer
toji May 17, 2019
2dbf9f1
Addressing some feedback
toji May 22, 2019
bed660f
Move direct output flag to render state
toji May 23, 2019
9b65d29
Comment about the WebGLRenderingContext's attributes taking precedenc…
toji May 23, 2019
458034b
Changed option to compositionDisabled
toji May 28, 2019
41c03e6
Fixed up explainer
toji May 29, 2019
006f5a1
Fixed a broken link to an outdated product
toji May 31, 2019
dfbc4bb
Change composition disabled to be implicit based on session type
toji Jun 12, 2019
a0a5310
Fixing a few loose ends
toji Jun 13, 2019
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Fixing a few loose ends
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@toji
toji committed Jun 13, 2019
commit a0a5310a6d0588bcd4a6fa8e1f98e5d6c5171c5d
4 changes: 1 addition & 3 deletions explainer.md
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Expand Up @@ -377,9 +377,7 @@ These scenarios can make use of inline sessions to render tracked content to the

The [`RelativeOrientationSensor`](https://w3c.github.io/orientation-sensor/#relativeorientationsensor) and [`AbsoluteOrientationSensor`](https://w3c.github.io/orientation-sensor/#absoluteorientationsensor) interfaces (see [Motion Sensors Explainer](https://w3c.github.io/motion-sensors/)) can be used to polyfill the first case.
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Not this PR, but boy does this sentence seem strange now that we're committed to inline.


To make use of this mode a `XRWebGLLayer` must be created with the `compositionDisabled` option set to `true`. This instructs the layer to not allocate a new WebGL framebuffer but instead set the `framebuffer` attribute to `null`. That way when `framebuffer` is bound all WebGL commands will naturally execute against the WebGL context's default framebuffer and display on the page like any other WebGL content. When that layer is set as the `XRRenderState`'s `baseLayer` the inline session is able to render it's output to the page.

Immersive and inline sessions can use the same render loop, but there are some differences in behavior to be aware of. Most importantly, inline sessions will not pump their render loop if they do not have a `baseLayer` with `compositionDisabled` set. (This restriction may be lifted in the future to enable more advanced effects.) Instead the session acts as though it has been [suspended](#handling-suspended-sessions) until a valid `baseLayer` has been assigned.
`XRWebGLLayer` created with an `inline` session will not allocate a new WebGL framebuffer but instead set the `framebuffer` attribute to `null`. That way when `framebuffer` is bound all WebGL commands will naturally execute against the WebGL context's default framebuffer and display on the page like any other WebGL content. When that layer is set as the `XRRenderState`'s `baseLayer` the inline session is able to render it's output to the page.

Immersive and inline sessions may run their render loops at at different rates. During immersive sessions the UA runs the rendering loop at the XR device's native refresh rate. During inline sessions the UA runs the rendering loop at the refresh rate of page (aligned with `window.requestAnimationFrame`.) The method of computation of `XRView` projection and view matrices also differs between immersive and inline sessions, with inline sessions taking into account the output canvas dimensions and possibly the position of the users head in relation to the canvas if that can be determined.

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2 changes: 1 addition & 1 deletion index.bs
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Expand Up @@ -1619,7 +1619,7 @@ The <dfn constructor for="XRWebGLLayer">XRWebGLLayer(|session|, |context|, |laye

</div>

Note: If a {{XRWebGLLayer}}'s {{XRWebGLLayerInit/composition disabled}} boolean is set to <code>true</code> all values on the {{XRWebGLLayerInit}} object are ignored, since the {{WebGLRenderingContext}}'s default framebuffer was already allocated using the context's [=actual context parameters=] and cannot be overridden.
Note: If a {{XRWebGLLayer}}'s {{XRWebGLLayer/composition disabled}} boolean is set to <code>true</code> all values on the {{XRWebGLLayerInit}} object are ignored, since the {{WebGLRenderingContext}}'s default framebuffer was already allocated using the context's [=actual context parameters=] and cannot be overridden.

The <dfn attribute for="XRWebGLLayer">context</dfn> attribute is the {{WebGLRenderingContext}} the {{XRWebGLLayer}} was created with.

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