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Re: [Public WebGL] Re: s3tc compression and UNPACK_FLIP_Y_WEBGL



On Mon, Sep 10, 2012 at 2:37 PM, Florian Bösch <pyalot@gmail.com> wrote:
> On Mon, Sep 10, 2012 at 11:32 PM, Brandon Jones <bajones@google.com> wrote:
>>
>> On Mon, Sep 10, 2012 at 2:23 PM, Jeff Russell <jeffdr@gmail.com> wrote:
>>>
>>> Flipping, at the very least, is doable without
>>> decompressing/recompressing the image...
>>
>>
>> Not necessarily. In order to properly flip the image you need to know the
>> details of the compression format, which the browser tries not to do. Since
>> I'm pretty sure that UNPACK_FLIP_Y_WEBGL affects the texture upload, rather
>> than flipping a bit in the driver, it's sensible to exclude compressed
>> textures from it's affected targets.
>>
>> Not that I wouldn't like to have it work everywhere, but I understand the
>> reasoning behind it.
>
> At least we should probably mention these little incoveniences somewhere
> because WebGL users are quite used to the fact that flip Y and
> generateMipmap just works (tm) and lest people just start throwing
> compressed textures into their code trusting their framework to glance over
> the details, they'll end up with garbage and errors.

Looking at the WebGL spec,
http://www.khronos.org/registry/webgl/specs/latest/#PIXEL_STORAGE_PARAMETERS
is pretty clear about those pixel storage parameters only affecting
calls to texImage2D and texSubImage2D. compressedTexImage2D and
compressedTexSubImage2D are notably absent. For this reason I don't
think any additional normative text is needed. However, if you have a
suggestion about non-normative text to add, please submit a pull
request on Github -- will be happy to review it.

Thanks,

-Ken

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