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Specified that XRWebGLLayer framebuffers always use premultiplied alpha #840

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toji merged 1 commit into from
Sep 19, 2019
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Specified that XRWebGLLayer framebuffers always use premultiplied alpha #840

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Expand Up @@ -1684,6 +1684,7 @@ An <dfn>opaque framebuffer</dfn> functions identically to a standard {{WebGLFram
- An [=opaque framebuffer=] initialized with {{XRWebGLLayerInit/depth}} <code>false</code> will not have an attached depth buffer.
- An [=opaque framebuffer=] initialized with {{XRWebGLLayerInit/stencil}} <code>false</code> will not have an attached stencil buffer.
- An [=opaque framebuffer=]'s color buffer will have an alpha channel if and only if {{XRWebGLLayerInit/alpha}} is <code>true</code>.
- The [=XR Compositor=] will assume the [=opaque framebuffer=] contains colors with premultiplied alpha. This is true regardless of the {{WebGLContextAttributes|premultipliedAlpha}} value set in the {{XRWebGLLayer/context}}'s [=actual context parameters=].
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@Manishearth Manishearth Sep 12, 2019

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If we do this we should probably also recommend a warning be displayed in this situation to properly fix #837

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@toji toji Sep 12, 2019

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I wondered about that, but it seems like recommending that the UA output a warning to the console falls outside of what specs typically dictate. At best we could put a non-normative note in that suggests it, but I'm not sure if the group feels like that's necessary?

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@Manishearth Manishearth Sep 12, 2019

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Yeah, a non normative note is what I meant. "UAs may want to show a warning to the console when a context created with premultipliedAlpha: false is passed to new XRWebGLLayer()"

We can also make it a hard error, but that might be too large a hammer.


NOTE: User agents are not required to respect <code>true</code> values of {{XRWebGLLayerInit/depth}} and {{XRWebGLLayerInit/stencil}}, which is similar to WebGL's behavior when [=create a drawing buffer|creating a drawing buffer=]

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