Tighten up spec text around frame timings, add hook for frame updates #897
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| @@ -863,7 +863,7 @@ When this method is invoked, the user agent MUST run the following steps: | |||
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| <div class="algorithm" data-algorithm="run-animation-frames"> | |||
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| When an {{XRSession}} |session| receives updated [=viewer=] state from the [=XRSession/XR device=], it runs an <dfn>XR animation frame</dfn> with a timestamp |now| and an {{XRFrame}} |frame|, which MUST run the following steps regardless of if the [=list of animation frame callbacks=] is empty or not: | |||
| When an {{XRSession}} |session| receives updated [=viewer=] state from the [=XRSession/XR device=], it runs an <dfn>XR animation frame</dfn> with a timestamp |now| and an {{XRFrame}} |frame| with [=XRFrame/time=] |now|, which MUST run the following steps regardless of if the [=list of animation frame callbacks=] is empty or not: | |||
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This doesn't feel like the right way to specify this. |now| and |frame| are both inputs to the algorithm, but the new text feels like an assignment happening in the algorithm description.
I'd suggest either:
- Assigning
[=XRFrame/time=]to|now|explicitly in the algorithm or - Removing |now| from the algorithm description altogether and using [=XRFrame/time=] in it's place elsewhere in the algorithm.
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Hm... I think we went to far in the other direction. We still need to have a declaration of the XRFrame somewhere.
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Not sure what you mean by that, it's constructed in the algorithm itself (as it should be, IMO, previously it just appeared out of the ether)
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Oh, my bad, i pushed up a partial commit because I forgot to save
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| </div> | ||
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| NOTE: Further specs may add new kinds of frame updates to these steps, e.g. for gamepad state. |
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This seems somewhat odd to me, but I'm not sure what else to suggest. Is there someone with experience with this sort of problem that we could get a sanity check from?
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An alternate plan was to have a "list of frame updates" (a list of callbacks) on the session and session with gamepads append a frame update to it. I felt that might get a bit unweildy though.
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Updated. |
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This makes it easier to do things like in immersive-web/webxr-gamepads-module#22 , where we want to be able to insert an action that occurs on the main thread whenever a frame is about to be processed.
r? @NellWaliczek