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Re: [Public WebGL] The state of MRTs



Sorry for coming to this discussion late -- was traveling.

It appears that only a tiny fraction of mobile devices support
multiple render targets today, and it looks like there's no
cross-vendor extension that could improve that situation in the short
term. For this reason, I think the WebGL WG should defer adding this
functionality to the extension registry and implementations. If
application developers make their content work with the current spec
they'll achieve maximum portability on current devices.

In the short term, I think the WG should focus on items for the next
version of the spec and implementation improvements: specifically,
resource sharing between contexts, access to WebGL from workers,
optional asynchronous context creation, performance improvements, and
better robustness to DoS issues.

-Ken


On Wed, Mar 21, 2012 at 8:29 AM, Benoit Jacob <bjacob@mozilla.com> wrote:
>
>
> ________________________________
>
> On Wed, Mar 21, 2012 at 9:21 AM, Benoit Jacob <bjacob@mozilla.com> wrote:
>>
>> Like for the other extensions that we recently agreed on, what would
>> probably help the most to get multiple render targets accepted would be
>> detailed analysis of what current mobile hardware can't support them, and
>> what is the prospect for the near future. Then we'll be able to see if a
>> compromise with portability makes sense. Sorry if that analysis was already
>> done in this thread, I admit I didn't read all of it.
>
>
> On desktops the core functionality is provided by the ARB_framebuffer_object
>
> ARB_framebuffer_object is, in my understanding, a hard requirement to be
> able to implement WebGL, as framebuffer objects are part of the WebGL API.
> So, this implies that support for multiple render targets is ubiquitous on
> desktop GL, except of course that GL_MAX_COLOR_ATTACHMENTS_EXT might be 1.
>
> On Direct3D the the number of render targets is found in
> D3DCAPS9.NumSumultaneousRTs.
>
> Nice, so the situation seems entirely clear on the desktop.
>
>
> Mobile support (505 devices, source [5]):
> - NV_draw_buffers  2.3% (12 devices)
> - NV_fbo_color_attachment 13.6% (69 devices)
> - Both: 13.6% (69 devices)
>
> Ouch. 13.6% is very little. Is the percentage much higher if we include only
> GPUs that still ship in new devices today?
>
> Benoit
>

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